Cardiac Rhythm Management Devices (Part I) - Angelfire

16 Pages·2001·0.22 MB·English

m REVIEW ARTICLE
Anesthesiology2001;95:1265–80 ©2001AmericanSocietyofAnesthesiologists,Inc.LippincottWilliams&Wilkins,Inc.
Cardiac Rhythm Management Devices (Part I)
Indications, Device Selection, and Function
JohnL.Atlee,M.D.,*AlanD.Bernstein,Eng.Sc.D.†
PACEMAKER1 and internal cardioverter–defibrillator tions and technology. In the second installment, we
(ICD) devices have undergone remarkable evolution discuss the potential for device malfunction in the hos-
since the first implantation of an asynchronous single- pital environments, perioperative management for pa-
chamber pacemaker1 in 1958 and of an ICD2 in 1980. tients with implanted devices, and care of patients dur-
Today, more than 500,000 patients in the United States ing device implantation or system revision.
have pacemakers, and up to 115,000 new devices are
implanted each year.3 The number of ICDs implanted
Indications for a Pacemaker or an ICD
each year has steadily increased, reaching 50,000 new
implants worldwide in 1999.4
Indications for a pacing or ICD device are considered
Contemporary single- and dual-chamber pacemakers
asclassI,II,orIII.10ClassIindicationsareconditionsfor
are sophisticated devices, with multiple programmable
which there is general agreement that a device may be
features, including recently introduced programmable
usefulandeffective(i.e.,isindicated).ClassIIindications
lead configuration5,6 and automatic mode-switching.7–9
are conditions in which a device is often used but for
Many devices use adaptive-rate pacing to modify the
which there is conflicting evidence or divergence of
pacing rate for changing metabolic needs. First-genera-
opinionastowhetheritisusefulandeffective(i.e.,may
tion ICDs were short-lived. A formal thoracotomy was
beindicated).ClassIIindicationsaresubdividedasIIaif
required for epicardial lead placement. Today, ICDs are
the weight of evidence or opinion is in favor of device
multiprogrammable, are longer-lived, have transvenous
usefulness or efficacy and IIb if usefulness or efficacy is
leads, and may incorporate all capabilities of contempo-
less well established. Finally, an indication is class III if
rary pacemakers.4 Furthermore, ICDs have multiple
there is general agreement that a device is unnecessary
tachycardia detection zones, with programmable detec-
and possibly even harmful (i.e., not indicated).
tioncriteriaandtieredtherapy(i.e.,antitachycardiapac-
ing [ATP], followed by shocks if needed) for each.4,10
Temporary Pacing Indications
ICDsalsostoredysrhythmiaeventrecordsandtreatment
Temporarypacingmayberequiredforratesupportin
results.Finally,clinicalexperiencewithaninternalatrial
patients who experience intermittent hemodynamically
cardioverter (atrioverter) has been reported.11–15
disadvantageous bradydysrhythmias or for stand-by pac-
In this first installment of a two-part communication,
ing in patients at increased risk for sudden high-degree
we discuss indications for implanted pacemakers or
atrioventricular(AV)heartblock(AVHB).Itisalsosome-
ICDs, provide an overview of how devices are selected,
timesusedtooverdriveorterminateatrialorventricular
and describe the basics of device design and function.
tachydysrhythmias. The endpoint for temporary pacing
Only brief mention is made of temporary pacing indica-
is resolution of the indication or implantation of a per-
manent pacemaker for a continuing indication. Trans-
venous endocardial16,17 or epicardial16,18 leads are most
Thisisthefirstpartofatwo-partarticle.PartIIwillappearin commonly used for temporary pacing. Noninvasive
theDecember2001issue.
transcutaneous and esophageal routes are also possi-
ble.19–21 Transcutaneous pacing produces simultaneous
ventricularandatrialcaptureandthusdoesnotpreserve
*ProfessorofAnesthesiology,MedicalCollegeofWisconsin. †AdjunctAs-
optimal hemodynamics in patients with intact atrioven-
sociateProfessor,Surgery,UniversityofMedicineandDentistryofNewJersey;
DirectorofTechnicalResearch,DepartmentofSurgery,andTechnicalDirector, tricular conduction. With available technology for
PacemakerCenter,NewarkBethIsraelMedicalCenter,Newark,NewJersey.
esophageal pacing, only atrial capture is reliable; thus,
ReceivedfromtheDepartmentofAnesthesiology,MedicalCollegeofWiscon-
sin,Milwaukee,Wisconsin,andtheDepartmentofSurgery,UniversityofMedi- the method is not suitable for patients with advanced
cineandDentistryofNewJersey,Newark,NewJersey.Submittedforpublication AVHB or atrial fibrillation.
March30,2000.AcceptedforpublicationJune25,2001.Supportwasprovided
solelyfrominstitutionaland/ordepartmentalsources. Indicationsfortemporarypacingarenotasestablished
AddressreprintrequeststoDr.Atlee:DepartmentofAnesthesiology,Froedtert asforpermanentpacemakers.Usualandlessestablished
MemorialLutheranHospital(East),9200WestWisconsinAvenue,Milwaukee,Wis- indicationsfortemporarytransvenousorepicardialpac-
consin53226.Addresselectronicmailto:[email protected]
maybepurchasedthroughtheJournalWebsite,www.anesthesiology.org. ing are listed in table 1.18,22–24 AVHB is classified as
Anesthesiology,V95,No5,Nov2001 1265
1266 J. L. ATLEE AND A. D. BERNSTEIN
Table1.UsualandLessEstablishedIndicationsforTemporaryCardiacPacing18,22–24
UsualIndications Less-establishedIndications
Sinusbradycardiaorlowerescaperhythmsduetoreversible DuringAMI:neworage-indeterminateRBBBwithLAFB,LPFB
causeandwithsymptomsorhemodynamiccompromise or1°AVHB,orwithLBBB;recurrentsinuspauses
Asbridgetopermanentpacingwithadvanced2°or3°AVHB, refractorytoatropine;overdrivepacingforincessantVT
regardlessofetiology DuringAMI:neworage-indeterminatebifascicularblockor
DuringAMI:asystole;newbifascicularblockwith1°AVHB; isolatedRBBB
alternatingBBB;symptomaticordisadvantageousbradycardia Heartsurgery:
notresponsivetodrugs;ortypeII2°AVHB Tooverdrivehemodynamicallydisadvantageous
Bradycardia-dependenttachydysrhythmias(e.g.,torsadesde atrioventricularjunctionalandventricularrhythms
pointeswithLQTS) ToterminatereentrantSVTorVT
Topreventpause-dependentorbradycardia-dependent
tachydysrhythmias
DuringtheinsertionofaPAcatheterinpatientwithLBBB
AVHB5atrioventricularheartblock;AMI5acutemyocardialinfarction;BBB5bundlebranchblock;LQTS5longQTintervalsyndrome,congenitaloracquired;
RBBB5rightbundlebranchblock;LAFB5leftanteriorfascicularblock;LPFB5leftposteriorfascicularblock;LBBB5leftbundlebranchblock;VT5
ventriculartachycardia;SVT5supraventriculartachycardia;PA5pulmonaryartery.
first-degree(1°),second-degree(2°),orthird-degree(3°; delay, progression to more advanced AVHB is unlikely,
complete) AVHB. Anatomically, it may occur above, andpacingisusuallynotindicated.10Withtype2°AVHB
within,orbelowtheHisbundle.10With1°AVHB,thePR withinorbelowtheHisbundle,symptomsarefrequent,
interval is greater than 0.20 s and is usually due to prognosis is poor, and progression to 3° AVHB is com-
atrioventricularnodeconductiondelay.25With2°AVHB, mon.10 Nonrandomized studies strongly suggest that
thereisgradualPRintervalprolongationbeforedropped pacingimprovessurvivalforpatientswith3°AVHBand
beats(typeIorWenckebach2°AVHB)ornoPRinterval symptoms.30–35 Pacing indications for acquired AVHB
prolongation (type II or Mobitz 2° AVHB). Type I 2° are listed in table 2.10,22,25
AVHBisusuallyassociatedwithanarrowQRScomplex, Chronic Bifascicular and Trifascicular Block. Ma-
and type II 2° AVHB with a wide QRS complex.10 In jor fascicles of the conduction system below the His
general, type I 2° AVHB with a narrow QRS complex
bundle are the right bundle branch and the left anterior
almost always occurs at the atrioventricular node.10
and posterior fascicles of the left bundle branch. The
When associated with bundle-branch block, there is in- latteractivatetheleftventricularfreewall.36Inaddition,
fra-Hisianblockinupto30%ofcases.25TypeII2°AVHB
septal branches of the left bundle branch supply the
is most commonly encountered when the QRS is pro-
middle third of the ventricular septum and provide the
longed and is generally localized to within the His-Pur-
earliest ventricular activation. Isolated block of any one
kinjesystem.25AdvancedtypeII2°AVHBreferstoblock
of these fascicles is unifascicular block. Left or right
of two or more consecutive P waves. With 3° AVHB
bundle-branch block with left anterior or posterior fas-
there is no association between atrial and ventricular
cicular block is bifascicular block. Block involving any
beats.
three fascicles is trifascicular block.
Electrocardiographic criteria for fascicular block are
Indications for a Permanent Pacemaker
described elsewhere.36 Syncope is common in patients
Chronic Atrioventricular Heart Block in Adults.
with bifascicular block but usually is not recurrent or
Patients with atrioventricular conduction abnormalities
associated with an increased incidence of sudden
may be asymptomatic or have symptoms related to bra-
death.37–39However,bifascicularblockwithperiodic3°
dycardia, ventricular dysrhythmias, or both. The pres-
AVHB and syncope is associated with an increased inci-
ence or absence of symptoms directly attributable to
denceofsuddendeath.40,41Thus,ifthecauseofsyncope
bradycardia has an important influence on the decision
to implant a permanent pacemaker.10 In addition, many with bifascicular or trifascicular heart block cannot be
indications for pacing with AVHB have evolved over 30 determined with certainty, or if concurrent drugs may
yr on the basis of experience rather than prospective exacerbate AVHB, prophylactic permanent pacing is in-
randomizedtrials,inpartbecausethereisnogoodalter- dicated, especially if syncope may have been due to
native treatment.10 intermittent3°AVHB.10Although3°AVHBismostoften
There is little evidence that pacing improves survival precededbybifascicularblock,therateofprogressionis
with isolated 1° AVHB,26 even though marked 1° AVHB slow (years). There is no evidence of acute progression
may be symptomatic without higher-degree AVHB.27 to 3° AVHB during anesthesia and surgery.42,43 Finally,
This may be because of the close proximity of atrial no one clinical or laboratory variable, including bifas-
systole to the preceding ventricular systole.28,29 With cicular block, can identify patients at high risk of death
typeI2°AVHBduetoatrioventricularnodeconduction from bradydysrhythmias with bundle-branch block.10,44
Anesthesiology,V95,No5,Nov2001
PACEMAKERS AND ICDs 1267
Table2.IndicationsforPermanentPacingwithAcquiredAtrioventricularHeartBlockinAdults
ClassI—Indicated ClassII—MayBeIndicated ClassIII—NotIndicated
3°AVHB: Asymptomatic3°AVHBwithaverage Asymptomatic1°AVHB
Symptomaticbradycardiaorneed rate.40beats/min TypeI,2°AVHBaboveHisbundle
fordrugscausingsame TypeII,2°AVHBwithoutsymptoms withoutsymptoms
Aftercatheterablationofthe (permanentorintermittent) AVHBthatisexpectedtoresolve
arterioventricularjunction TypeI,2°AVHBatorbelowHisbundle
Postoperativeandnotexpectedto withoutsymptoms
resolve 1°AVHBwithsymptomsoflowcardiac
Neuromusculardiseases outputthatarerelievedbytemporary
Escaperhythm,40beats/minor pacing
asystole.3.0sinan Marked1°AVHBinapatientwithCHF
asymptomaticpatient
2°AVHBthatispermanentor
intermittent,withsymptomatic
bradycardia
AVHB5arterioventricularheartblock;CHF5congestiveheartfailure.
AdaptedfromGregoratosG,CheitlinM,ConillA,EpsteinA,FellowsC,FergusonTJ,FreedmanR,HlatkyM,NaccarelliG,SaksenaS,SchlantR,SilkaM:
ACC/AHAguidelinesforimplantationofcardiacpacemakersandantiarrhythmiadevices:AreportoftheACC/AHATaskForceonPracticeGuidelines(Committee
onPacemakerImplantation).JAmCollCardiol1998;31:1175–209.Copyright1998bytheAmericanCollegeofCardiologyandtheAmericanHeartAssociation.
Permissiongrantedforone-timeuse.FurtherreproductionisnotpermittedwithoutpermissionoftheACC/AHA.
Pacingindicationsforchronicbifascicularandtrifascicu- or sinoatrial block, with or without escape rhythms. It
lar block are summarized in table 3.10,25 often occurs in association with paroxysmal supraven-
Atrioventricular Heart Block after Acute Myocar- tricular tachydysrhythmias (bradycardia–tachycardia syn-
dial Infarction. Pacing indications after acute myocar- drome). Sinus bradycardia due to increased vagal tone is
dial infarction (AMI) are largely related to the presence physiologic in trained athletes, who may have sleeping
of intraventricular conduction defects and not necessar- heart rates as low as 30 beats/min, with sinus pauses or
ily to symptoms.10 The requirement for temporary pac- typeI2°AVHB.10Patientswithsinusnodedysfunctionmay
ingwithAMIdoesnotinevitablyconstituteanindication have symptoms due to bradycardia, tachycardia, or both.
for permanent pacing.23 The long-term prognosis for Correlation of symptoms with dysrhythmias is essential10
survivors of AMI is related primarily to the extent of and is established by ambulatory monitoring. Sinus node
myocardialinjuryandnatureofintraventricularconduc- dysfunctionmayalsopresentasadeficientrateresponseto
tion defects rather than to AVHB itself.10,34,45–48 With stress or exercise (i.e., chronotropic incompetence). An
the exception of isolated left anterior fascicular block, adaptive-rate pacemaker may benefit these patients by re-
AMI patients with intraventricular conduction distur- storingmorephysiologicheartrates.10,50,51Althoughsinus
banceshaveunfavorableshort-andlong-termprognoses, node dysfunction is often the primary indication for a
withincreasedriskofsuddendeath.10,34,45,47Thisprog- pacemaker,50 pacing does not necessarily improve surviv-
nosis is not necessarily due to the development of high- al.52,53 However, symptoms due to bradycardia may be
grade AVHB,10 although the incidence of high-grade relieved. Nonrandomized studies suggest that dual-cham-
AVHBishigheramongthesepatients.45,49Pacingindica- ber pacing improves survival more than ventricular pac-
tions for AVHB after AMI are listed in table 4.10 ing.10Asinglerandomized,prospectivetrialofatrialversus
Sinus Node Dysfunction. Sinus node dysfunction ventricular pacing found significantly higher rates of sur-
maymanifestassinusbradycardia,sinuspauseorarrest, vival,lessatrialfibrillation,fewerthromboemboliccompli-
Table3.IndicationsforPermanentPacingwithLong-termBifascicularandTrifascicularBlock
ClassI—Indicated ClassII—MayBeIndicated ClassIII—NotIndicated
Intermittent3°AVHBassociated BFBorTFBblockwithsyncopenot BFBorTFBwithoutAVHBor
withsymptoms provenduetoAVHB,butother symptoms
TypeII,2°AVHBwithsymptoms causesofsyncopearenot BFBorTFBwith1°AVHBwithout
identifiable(specifically,VT) symptoms
HVinterval.100msorpacing-
inducedinfra-Hisianblock
AVHB5atrioventricularheartblock;BFBorTFB5bifascicularortrifascicularblock;VT5ventriculartachycardia;HVinterval5His-Purkinjeconductiontime.
AdaptedfromGregoratosG,CheitlinM,ConillA,EpsteinA,FellowsC,FergusonTJ,FreedmanR,HlatkyM,NaccarelliG,SaksenaS,SchlantR,SilkaM:
ACC/AHAguidelinesforimplantationofcardiacpacemakersandantiarrhythmiadevices:AreportoftheACC/AHATaskForceonPracticeGuidelines(Committee
onPacemakerImplantation).JAmCollCardiol1998;31:1175–209.Copyright1998bytheAmericanCollegeofCardiologyandtheAmericanHeartAssociation.
Permissiongrantedforone-timeuse.FurtherreproductionisnotpermittedwithoutpermissionoftheACC/AHA.
Anesthesiology,V95,No5,Nov2001
1268 J. L. ATLEE AND A. D. BERNSTEIN
Table4.IndicationsforPacingforAtrioventricularHeartBlockafterAcuteMyocardialInfarction
ClassI—Indicated ClassII—MayBeIndicated ClassIII—NotIndicated
Persistent2°or3°AVHBintheHis-Purkinje Persistent2°or3°AVHBatthe TransientAVHBwithoutintraventricular
system atrioventricularnode conductiondefectsorwithisolatedLAFB
Transient2°or3°infranodalAVHBwithBBB AcquiredLAFBwithoutAVHB
Symptomatic2°or3°AVHBatanylevel Persistent1°AVHBwitholdorage-
indeterminateBBB
AVHB5atrioventricularheartblock;BBB5bundlebranchblock;LAFB5leftanteriorfascicularblock
AdaptedfromGregoratosG,CheitlinM,ConillA,EpsteinA,FellowsC,FergusonTJ,FreedmanR,HlatkyM,NaccarelliG,SaksenaS,SchlantR,SilkaM:
ACC/AHAguidelinesforimplantationofcardiacpacemakersandantiarrhythmiadevices:AreportoftheACC/AHATaskForceonPracticeGuidelines(Committee
onPacemakerImplantation).JAmCollCardiol1998;31:1175–209.Copyright1998bytheAmericanCollegeofCardiologyandtheAmericanHeartAssociation.
Permissiongrantedforone-timeuse.FurtherreproductionisnotpermittedwithoutpermissionoftheACC/AHA.
cations, less heart failure, and reduced risk of AVHB with since many patients have bradycardia after the onset of
atrial pacing than with ventricular pacing after 8 yr of hypotension. Nonetheless, there was an 85% reduction
follow-up.54Pacingindicationsforsinusnodedysfunction in risk of recurrent syncope in patients randomized to
aresummarizedintable5.10 dual-chamber pacing in one recent study.57 Indications
Hypersensitive Carotid Sinus and Neurally Medi- forpacingwithhypersensitivecarotidsinusandneurally
ated Syndromes. Hypersensitive carotid sinus syn- mediated syndromes are summarized in table 6.10
drome is an uncommon cause for syncope.10 It is syn- Pacing in Children and Adolescents. Pacemakers
cope or presyncope due to an exaggerated response to areprescribedforchildrenandadolescentswithsymptom-
carotid sinus stimulation. Before a pacemaker can be aticbradycardiaduetosinusnodedysfunctionandcongen-
prescribed, the relative contribution of cardioinhibitory ital or acquired advanced 2° or 3° AVHB. Although indi-
components (bradycardia, asystole, and AVHB) and va- cationsforpacingaresimilarinchildrenandadults,there
sodepressor components (vasodilation with hypoten- are additional considerations with regard to children.10
sion) must be determined. A hyperactive carotid sinus First is heart rate. Whereas a rate of 45 beats/min may be
response is defined as asystole greater than 3 s due to normal for an adolescent, it is abnormal for a neonate.
sinus arrest or AVHB, an abrupt reduction in blood Second, survivors of corrective or palliative surgery for
pressure, or both.55 With a pure excessive cardioinhibi- congenital heart disease with persistent ventricular dys-
tory response, pacing effectively relieves symptoms.10 functionandalteredcirculatoryphysiologymayhavesymp-
However, because 10–20% of patients have a mixed tomatic bradycardia at heart rates that do not produce
response, attention to both components is essential for symptoms in normal children. Hence, pacing indications
effective therapy.10 arebasedmoreoncorrelationofsymptomswithbradycar-
Neurally mediated syncope accounts for 10–40% of dia than on arbitrary rate criteria. Finally, pacing is indi-
patients with syncope.10 It includes a variety of clinical cated for bradycardia only after exclusion of other causes
scenariosinwhichtriggeringofaneuralreflexresultsin (e.g., seizures, breath-holding, apnea, and neurally medi-
a self-limited episode of bradycardia and hypotension.56 atedmechanisms).
Vasovagalsyncopeisacommonpresentation.10Theuse Indications for permanent pacing for congenital 3°
ofpermanentpacinginthesepatientsiscontroversial,10 AVHB have evolved on the basis of increased definition
Table5.IndicationsforPacingwithSinusNodeDysfunction
ClassI—Indicated ClassII—MayBeIndicated ClassIII—NotIndicated
SNDwithdocumentedsymptomatic SND,occurringspontaneouslyoras SNDinasymptomaticpatients,including
bradycardia,whichmayberesultof resultofnecessarydrugtherapy,with thoseinwhomsubstantialsinus
drugtherapy;insomepatients,thiswill heartrates,40beats/minwithout bradycardia(heartrate,40beats/min)
resultfromlong-term,requireddrug clearassociationbetweensignificant isconsequenttolong-termdrug
therapy(i.e.,nogoodalternative; symptomsandbradycardia treatment
reduceddosenotpossible) SNDinminimallysymptomaticpatients, SNDwithsymptomsofbradycardia,but
Symptomaticchronotropicincompetence chronicheartrate,30beats/min thatareclearlydocumentedasnot
whileawake associatedwithbradycardia
SNDwithsymptomaticbradycardiadue
tononessentialdrugtherapy
SND5sinusnodedysfunction.
AdaptedfromGregoratosG,CheitlinM,ConillA,EpsteinA,FellowsC,FergusonTJ,FreedmanR,HlatkyM,NaccarelliG,SaksenaS,SchlantR,SilkaM:
ACC/AHAguidelinesforimplantationofcardiacpacemakersandantiarrhythmiadevices:AreportoftheACC/AHATaskForceonPracticeGuidelines(Committee
onPacemakerImplantation).JAmCollCardiol1998;31:1175–209.Copyright1998bytheAmericanCollegeofCardiologyandtheAmericanHeartAssociation.
Permissiongrantedforone-timeuse.FurtherreproductionisnotpermittedwithoutpermissionoftheACC/AHA.
Anesthesiology,V95,No5,Nov2001
PACEMAKERS AND ICDs 1269
Table6.IndicationsforPacingwithHypersensitiveCarotidSinusandNeurallyMediatedSyndromes
ClassI—Indicated ClassII—MayBeIndicated ClassIII—NotIndicated
Recurrentsyncopecausedbycarotid Recurrentsyncopewithoutclear Hyperactivecardioinhibitoryresponse
sinusstimulation;minimalcarotid provocativeeventsandwitha tocarotidsinusstimulation,butno
sinuspressureinducesasystole.3s hypersensitivecardioinhibitory symptoms
durationintheabsenceofdrugsthat response Hyperactivecardioinhibitoryresponse
depressthesinusnodeor Neurallymediatedsyncopewith tocarotidsinusstimulationwith
atrioventricularconduction significantbradycardiareproduced vaguesymptomssuchasdizziness,
byahead-uptiltwithorwithout light-headedness,orboth
provocativemaneuvers Recurrentsyncope,light-headedness,
(isoproterenol) ordizzinessintheabsenceofa
hyperactivecardioinhibitoryresponse
Situationalvasovagalsyncopeinwhich
avoidancebehavioriseffective
AdaptedfromGregoratosG,CheitlinM,ConillA,EpsteinA,FellowsC,FergusonTJ,FreedmanR,HlatkyM,NaccarelliG,SaksenaS,SchlantR,SilkaM:
ACC/AHAguidelinesforimplantationofcardiacpacemakersandantiarrhythmiadevices:AreportoftheACC/AHATaskForceonPracticeGuidelines(Committee
onPacemakerImplantation).JAmCollCardiol1998;31:1175–209.Copyright1998bytheAmericanCollegeofCardiologyandtheAmericanHeartAssociation.
Permissiongrantedforone-timeuse.FurtherreproductionisnotpermittedwithoutpermissionoftheACC/AHA.
of the natural history of the disease, as well as advances whichpacingmightimprovetheLVoutflowobstruction
in technology and diagnosis. For example, pacing may are unclear but possibly involve changes in the ventric-
improve long-term survival and prevent syncope in se- ularcontractionpattern.10Selectionofoptimalatrioven-
lected patients with congenital complete AVHB.58,59 A tricular delay appears critical to achieving a beneficial
number of criteria, including average heart rate, QT hemodynamic result.70,75
interval duration, exercise tolerance, and associated Dilated Cardiomyopathy. Several observational
structural heart disease, are weighed before pacemaker studies show hemodynamic improvement after institu-
implantation in asymptomatic patients.10 tion of dual-chamber pacing with short atrioventricular
For patients with chronic advanced 2° or 3° AVHB delay for dilated cardiomyopathy.76–79 Possibly, well-
followingcardiacsurgery,theprognosisispoorwithout timed atrial contractions prime the ventricles and de-
pacing.60However,theneedforpacinginpatientswith
crease mitral regurgitation, thereby augmenting stroke
residual bifascicular heart block and intermittent AVHB volume and arterial pressure.10 Greater improvement
is less certain.10 Before a device is implanted, the em-
may be obtained with atrioventricular synchronous
bolic risk of residual intracardiac defects and require-
biventricular pacing than with single-site right ventricu-
mentforlifelongpacingmustbeconsidered.Thebrady-
lar pacing in patients with intraventricular conduction
cardia–tachycardia syndrome commonly occurs
block and end-stage heart failure.80
following congenital heart surgery.61 Both antibradycar-
Cardiac Transplantation. The incidence of brady-
dia and ATP have been used for treatment,62,63 but the
dysrhythmiasaftercardiactransplantationrangesfrom8
results are equivocal.10,61,64,65 Nonetheless, symptom-
to 23%, with the majority of occurrences due to sinus
atic bradycardia and proarrhythmia with drugs (i.e.,
node dysfunction.10 Because of symptoms and delayed
provocation of new or worse dysrhythmias) limit their
rehabilitation, some centers are more aggressive with
usefulness for treatment. Thus, pacing is weighed as
pacing for persistent postoperative bradycardia. How-
adjunctive therapy for the bradycardia–tachycardia syn-
drome.10 Finally, the use of pacing and b-blockers in ever, because one half of patients with bradydysrhyth-
miasaftercardiactransplantationshowimprovementby
patients with congenital long QT syndrome has sup-
port,66,67especiallyincasesofpause-dependentventric- 1 yr, long-term pacing may be unnecessary.10,81,82
Termination and Prevention of Tachydysrhyth-
ular tachydysrhythmias. Pacing indications for children
and adolescents are summarized in table 7.10 mias by Pacing. Pacing can terminate a variety of
tachydysrhythmias, including atrial flutter, paroxysmal
Miscellaneous Pacing Indications.
Hypertrophic Obstructive Cardiomyopathy. A reentrant supraventricular tachycardia (SVT), and ven-
dual-chamber pacemaker with a short atrioventricular triculartachycardia(VT).10Anumberofpacingpatterns
delay reduces the magnitude of left-ventricular outflow are used, including programmed extrastimulation and
tract obstruction and alleviates symptoms in patients short bursts of rapid pacing. Although use of dedicated
withseverelysymptomaticobstructivehypertrophiccar- antitachycardia pacemakers has been reported,83 today
diomyopathy.68–70 Recent trials confirm this and also thiscapabilityismorelikelytobeincorporatedinanICD
demonstrate improvement in functional status.71,72 device as part of a tiered antidysrhythmia therapy (be-
However,theperceivedsymptomaticimprovementmay low). Pacing and b-blockers are used to prevent dys-
belittlemorethanaplaceboeffect.73,74Mechanismsby rhythmiaswithcongenitallongQTsyndrome66,67andto
Anesthesiology,V95,No5,Nov2001
1270 J. L. ATLEE AND A. D. BERNSTEIN
Table7.IndicationsforPacinginChildrenandAdolescents
ClassI—Indicated ClassII—MayBeIndicated ClassIII—NotIndicated
Advanced2°or3°AVHBwith BTSwiththeneedforlong-termantiarrhythmic TransientpostoperativeAVHB:
symptomaticbradycardia,lowcardiac drugtreatment(exceptdigitalis) returnofnormalatrioventricular
output,orCHF Congenital3°AVHBafterage1yr;averagerate, conductionwithin7days
SNDwithcorrelationofsymptoms 50beats/minorpauses2–33basiccyclelength Postoperativebifascicularblock,
duringage-inappropriatebradycardia LQTSwithtypeII,2°or3°AVHB withorwithout1°AVHB,and
Postoperative2°or3°AVHBnot ComplexCHD:asymptomaticsinusbradycardia nosymptoms
expectedtoresolveorthatpersistsat withrestingrate,35beats/minorpauses.3s AsymptomatictypeI,2°AVHB
least7days Transientpostoperative3°AVHB;returnofnormal Sinusbradycardiawithout
Congenital3°AVHBwithwideQRS atrioventricularconductionby7days symptomsinadolescentswith
escaperhythmorventricular Asymptomaticpostoperativebifascicularblock,with CHD,whenlongestR-Rinterval
dysfunction orwithout1°AVHB is,3sandminimumrate.
Congenital3°AVHBinaninfantwith AsymptomatictypeI,2°AVHB 40beats/min
rates,50–55beats/minorCHDand Adolescents:asymptomaticsinusbradycardia
rates,70beats/min (longestR-Rinterval,3s;minimumrate.40
Sustained,pause-dependentVT,withor beats/min)
withoutlongQT,inwhichtheefficacy
ofpacingisthoroughlydocumented
AVHB 5 atrioventricular heart block; CHF 5 congestive heart failure; SND 5 sinus node dysfunction; CHD 5 congenital heart disease; VT 5 ventricular
tachycardia;BTS5bradycardia-tachycardiasyndrome;LQTS5longQTsyndrome.
AdaptedfromGregoratosG,CheitlinM,ConillA,EpsteinA,FellowsC,FergusonTJ,FreedmanR,HlatkyM,NaccarelliG,SaksenaS,SchlantR,SilkaM:
ACC/AHAguidelinesforimplantationofcardiacpacemakersandantiarrhythmiadevices:AreportoftheACC/AHATaskForceonPracticeGuidelines(Committee
onPacemakerImplantation).JAmCollCardiol1998;31:1175–209.Copyright1998bytheAmericanCollegeofCardiologyandtheAmericanHeartAssociation.
Permissiongrantedforone-timeuse.FurtherreproductionisnotpermittedwithoutpermissionoftheACC/AHA.
prevent recurrences of paroxysmal SVT84 and bradycar- However, both groups derive a significant survival ben-
dia-dependent atrial fibrillation.85–88 efit with ICDs in comparison with the benefit of drug
treatment alone.100
Indications for ICDs Drugs and surgical or catheter ablation are other op-
AnICDcanbeusedforthepreventionofsuddendeath tions to reduce or prevent VT or VF in at-risk patients,
in a patient with life-threatening ventricular tachydys- although drugs and ICDs together may improve quality
rhythmias.10 An implanted atrial ICD89 or combined oflifebyreducingtheneedforshocks.10Whereasserial
atrial and ventricular ICD90 may be prescribed for pa- electrophysiologic testing or Holter monitoring is used
tients with paroxysmal atrial tachydysrhythmias or sus- toguidedrugtherapy,maintainingeffectivetherapymay
ceptibility to both atrial and ventricular tachydysrhyth- be difficult because of intolerance and prodysrhythmia
mias. However, there is no consensus with regard to or adverse effects with prolonged use.101,102 Although
indications for use of these devices. b-blockers do reduce mortality after acute infarc-
It has been clearly shown in prospective clinical trials tion,103,104 there are no data to support the use of
thatICDsrevertsustainedVTandventricularfibrillation b-blockers as single therapy for ventricular tachydys-
(VF).ICDsterminateVFsuccessfullyinmorethan98%of rhythmias.10,100 Class III drugs, especially amiodarone,
episodes.91,92 When an ICD is used with tiered therapy, areassociatedwithsignificantlylowerratesoftachydys-
VTisconvertedwithATPin89%91to96%93ofepisodes. rhythmia recurrence, sudden death, and total mortali-
Inappropriate ICD therapy, namely, high-energy shocks ty.10,100 AVID, a large, prospective, randomized trial,
delivered for misdiagnosed dysrhythmias, is adminis- compared long-term therapy with ICDs and class III
tered to 5–11% of patients. Availability of stored events drugs for survivors of cardiac arrest and patients with
has made it possible to estimate the benefit of ICDs in unstable VT.100 For ICDs and drugs, unadjusted survival
the absence of placebo-controlled studies.94–97 In these estimates at 1 yr were 89% and 82%; at 2 yr, 82% and
studies,ICDshaveachievedgreaterthan98%conversion 75%;andat3yr,75%and64%,respectively.WithICDs,
of VF or VT with circulatory collapse, with a significant theestimatedrelativeriskreductionwas39%at1yrand
projected survival benefit in comparison with that in 31% at 3 yr.
untreatedpopulations.94Thisbenefitisincrementaland Radio-frequency current ablation is most effective for
continuestoincreaseupto4yr.Asimilarbenefitexists sustained monomorphic VT induced during electro-
for patients with sustained VT.95 In addition, survival of physiologic study or cardiac surgery and mapped to
patientswithICDsisinfluencedbyleftventricularfunc- specific ventricular sites.10 Surgical experience is more
tion.Survivalamongpatientswithaleftventricularejec- extensive and favorable for patients with coronary dis-
tionfractiongreaterthanorequalto30%islowerat3yr ease, and low recurrence rates (, 10% at 2 yr) and
than among those with higher ejection fractions.98,99 minimal sudden death rates have been reported.105-107
Anesthesiology,V95,No5,Nov2001
PACEMAKERS AND ICDs 1271
Table8.IndicationsforICDTherapyforPrimaryorSecondaryPrevention
ClassI—Indicated ClassII—MayBeIndicated ClassIII—NotIndicated
CardiacarrestduetoVT/VFnotduetoa CardiacarrestpresumedduetoVT/VF: Syncopeofundeterminedcause;no
transientorreversiblecause othermedicalconditionsprecludeEPS inducibleVT/VF
SpontaneoussustainedVT SeverelysymptomaticVTbeforeheart IncessantVT/VF
Syncopeofundeterminedoriginwith transplantation VT/VFconsequenttoSVTorVTamenable
clinicallyrelevant,hemodynamically LQTS,HCM,andotherfamilialconditions tosurgicalorcatheterablation(WPW;
significantsustainedVTorVFinduced withahighriskforlife-threatening specifictypesofVT*)
atEPSwhendrugtherapyis ventriculardysrhythmias VentricularVT/VFduetoatransientor
ineffective,nottolerated,ornot InduciblesustainedVT/VFinpatientwith reversiblecause
preferred NSVT,CAD,oldMI,andLVdysfunction Psychiatricillnessesthatmaybe
NSVTwithCAD,previousMI,LV Recurrentsyncopeofundetermined aggravatedbyICDimplantationor
dysfunction,andinducibleVFor etiologyinthepresenceofventricular precludessystematicfollow-up
sustainedVTatEPSnotsuppressed dysfunctionandinducibleventricular Terminalillnesswith#6monthslife
byaclassIantidysrhythmia dysrhythmiasatEPSifothercausesof expectancy
syncopehavebeenexcluded AfterCABG:prolongedQRS;LV
dysfunction;nospontaneous/inducibleVT
Drug-refractory,ClassIV(NYHA)CHF:not
candidateforhearttransplantation
*SpecificVTincludesidiopathicleftventricular,rightventricularoutflowtract,andbundlebranchorfascicularVT.
VT5ventriculartachycardia;VF5ventricularfibrillation;EPS5electrophysiologicalstudy;NSVT5nonsustainedVT;CAD5coronaryarterydisease;MI5
myocardialinfarction;LV5leftventricular;LQTS5longQTsyndrome;HCM5hypertrophiccardiomyopathy;SVT5supraventriculartachydysrhythmias;
WPW 5 Wolff-Parkinson-White syndrome; ICD 5 internal cardioverter–defibrillator; CABG 5 coronary artery bypass surgery; NYHA 5 New York Heart
Association.
AdaptedfromGregoratosG,CheitlinM,ConillA,EpsteinA,FellowsC,FergusonTJ,FreedmanR,HlatkyM,NaccarelliG,SaksenaS,SchlantR,SilkaM:
ACC/AHAguidelinesforimplantationofcardiacpacemakersandantiarrhythmiadevices:AreportoftheACC/AHATaskForceonPracticeGuidelines(Committee
onPacemakerImplantation).JAmCollCardiol1998;31:1175–209.Copyright1998bytheAmericanCollegeofCardiologyandtheAmericanHeartAssociation.
Permissiongrantedforone-timeuse.FurtherreproductionisnotpermittedwithoutpermissionoftheACC/AHA.
Catheterablationismosteffectivewithrightventricular portant treatment option for young patients with con-
outflow tract VT, idiopathic left septal VT, and bundle genitalheartdisease,cardiomyopathies,orprimaryelec-
branch reentrant VT.108–110 Multiple VT morphologies trical disease (e.g., long QT syndrome), patients with
and polymorphic VT, along with progressive cardiomy- malignantdysrhythmias,andsuddendeathsurvivors.10A
opathy, are less amenable to a favorable result with family history of sudden death may also influence the
catheter ablation.10 decision to implant an ICD.67,111,119
Use of ICDs is prescribed for secondary prevention in Finally,ICDsareusedforprimarypreventioninpatients
patients who have coronary artery disease and a history with asymptomatic coronary artery disease and nonsus-
of sudden death or who have documented or inducible tainedventriculartachydysrhythmias.112,120 Othercircum-
sustainedventriculartachydysrhythmias.10Suchpatients stancesinwhichICDshavebeenusedforprimarypreven-
accountforthemajorityofthosereceivingICDs.10ICDs tionincludefollowingcoronaryarterybypasssurgeryin
are widely accepted for improving outcomes for these patients with severe left ventricular dysfunction (ejec-
patients. ICDs are also indicated for patients with long tion fraction , 35%) and after abnormal findings of
QT syndrome and recurrent syncope, sustained ventric- signal-averaged electrocardiography,121 as well as in
ulardysrhythmias,orsuddencardiacdeathdespitedrug some patients awaiting heart transplantation.10, 122, 123
therapy.67,111,112ICDsareprescribedalongwithclassIA However, with the latter, the benefit is diluted by some
antidysrhythmic drugs (mostly quinidine) for patients patients’deathdueto heartfailure. Indications forICDs
with idiopathic VF or the Brugada syndrome.113 The are summarized in table 8.10
latteristheassociationofrightbundle-branchblockand
ST-segment elevation (electrocardiographic leads V1– Device Selection
V3) with sudden death in patients without confirmed Temporary Pacing. Transvenous (endocardial), epi-
heart disease.114,115 Sudden death survivors with hyper- cardial, transesophageal, and transcutaneous routes are
trophic cardiomyopathy are considered for ICD therapy used for temporary pacing. The first two routes are
in preference to or with drugs.10,116 ICDs are used as consideredinvasive(e.g.,riskofsepsis,directmyocardial
prophylaxis for syncope and sudden death with drug- damage, or cardiac perforation with tamponade), and
refractorydysrhythmiasanddysrhythmogenicrightven- thelattertwopacingroutesareconsiderednoninvasive.
tricular dysplasia.117 Fewer than 1% of ICD implants are Discussion of the pros and cons of each, as well as
for primary prevention in pediatric patients.118 How- methods and equipment, is beyond the scope of this
ever, the need for lifelong drug therapy, with possible article. The interested reader is referred to previous
noncompliance and adverse effects, makes ICDs an im- publications.16,18,19,24
Anesthesiology,V95,No5,Nov2001
1272 J. L. ATLEE AND A. D. BERNSTEIN
Selection of a Permanent Pacemaker. Single- and ble to noninvasively switch back and forth between
dual-chamber pulse generators vary in size, battery ca- unipolar and bipolar lead configurations. With the
pacity, cost, and unipolar or bipolar electrode configu- former, all or part all of the pulse generator metal hous-
ration (below). They may incorporate sensor-modulated ing(can)servesastheanode(1)andthedistalelectrode
adaptive-rate pacing, programmable polarity, and/or au- of the bipolar lead as cathode (2). With the bipolar
tomatic mode-switching. Pacing leads vary in electrode configuration, proximal and distal lead electrodes serve
configuration, insulation material, methods for fixation, as anode and cathode, respectively. The ability to pro-
stimulation impedance, and presence of steroid elution. gram unipolar pacing is necessary if lead insulation or
Otherfactorsthatinfluencepacemakerselectionarethe conductor failure occurs in a bipolar lead system.6 In
pacemaker programming device capabilities and access addition, the ability to program separate lead configura-
totechnicalsupport.Foralldevices,pacingmode,pulse tions for sensing and pacing permits exploitation of
amplitude and width, sensitivity, lower rate, and refrac- eitherwhileminimizingdisadvantages(e.g.,oversensing
tory periods are programmable. For dual-chamber de- with unipolar leads).5,6 Dual-chamber pacemakers with
vices, the atrioventricular interval and maximum track- automatic mode-switching are used for patients with
ing rate are also programmable. With adaptive-rate
AVHB and susceptibility to paroxysmal atrial tachydys-
pacemakers,severalrate-modulationparametersarepro-
rhythmias. Algorithms detect rapid, nonphysiologic
grammable. Implanting physicians must also anticipate
atrialratesandautomaticallyswitchthepacingmodeto
the progression of cardiac rhythm abnormalities when
one that excludes atrial tracking and the associated risk
selecting and programming a device.10 For example,
of ventricular pacing at or near the programmed maxi-
patients with sinus node dysfunction and susceptibility mal rate.7–9,131
to paroxysmal atrial tachydysrhythmias might develop
Pacemaker Leads. Most contemporary pacemakers
AVHB due to needed drug therapy, disease progression,
use transvenous (endocardial) leads. Bipolar leads are
or catheter ablation for modification of atrioventricular
being used increasingly worldwide.6 Bipolar sensing re-
conduction. If so, a dual-chamber pacemaker with auto-
duces risk of inappropriate pacing inhibition or stimula-
matic mode-switching might be indicated. Finally, the
tion due to oversensing. However, with some bipolar
patientwithanindicationforpacingandatriskforVTor
leads, there has been an unacceptably high failure rate
VF will receive a single- or dual-chamber ICD, since all
due to lead insulation degradation,10 although newer
ICDs today have a single- or dual-chamber pacing capa-
lead designs have improved on this.132,133 An important
bility, and many have adaptive-rate pacing as well.
advance has been development of steroid-eluting
Adaptive-rate Pacemakers. A 1996 industry-wide
leads.6,10 These have a small reservoir of corticosteroid
survey in the United States indicated that adaptive-rate
that is slowly released into the electrode–tissue inter-
pacing was a programmable option in 83% of all im-
face, reducing inflammation, fibrosis, and chronic cap-
planted pulse generators.10 In patients with chrono-
ture thresholds.
tropic incompetence, adaptive-rate pacing improves ex-
ercise capacity and quality of life.10 Most sensors are Selection of an ICD. Many of the above consider-
ationsapplytoICDselection,sincetheyfeatureantibra-
piezoelectric crystals or accelerometers that detect mo-
tion,acceleration,vibration,orpressure.10,124Neverthe- dycardiapacingaswellasATPandshocksfortachydys-
less, minute ventilation125 or stimulus-to-T interval126 rhythmias. A primary feature that distinguishes
contemporaryICDsfromearliermodelsistheavailability
sensors may provide a rate response more proportional
to exercise.10 of ATP as a programmable option. Although ATP in-
creases pulse generator cost, it is useful in a majority of
Single-pass Lead Systems. Commonly, dual-cham-
patients receiving ICDs, since it converts up to 96% of
ber devices have a separate atrial lead to detect atrial
depolarization in patients with sinus node dysfunction. episodesofVTwithouttheneedforshocks.93Nonetheless,
Single-pass leads have both atrial and ventricular elec- ATP may accelerate VT in 2–6% of episodes,93,134,135 al-
trodes, negating the need for separate leads.6 However, though this may be influenced by whether the pacing
it was found that the amplitude of sensed signals with algorithm to terminate VT is used empirically or on the
separate,floatingatrialleadswasinconsistentandvaried basis of results of electrophysiologic testing.135 Patients
significantly with changes in posture.127,128 In addition, with only VF before ICD implantation are less likely to
atrial pacing was not possible. With newer, single-pass subsequentlyhaveVTdetectedbytheirICDs.136However,
leads, the atrial signal amplitude is higher and dual- theincidenceofVTinthesepatients(18%)issignificant136;
chamber pacing is possible.129,130 thus,itisdesirabletohaveATPasaprogrammablefeature
Programmable Lead Configuration and Auto- ofICDs,evenwithoutahistoryofVT.4,10Finally,ICDswith
matic Mode-switching. Most contemporary pacemak- dual-chamber pacing and sensing are appropriate for pa-
ers offer separately programmable lead configurations tientswhorequiredual-chamberpacingandtherapyforVT
forbothpacingandsensingintheatriumandventricle.6 or VF or who have atrial dysrhythmias that might trigger
Thus, if the pacing system uses bipolar leads, it is possi- inappropriateICDtherapies.10
Anesthesiology,V95,No5,Nov2001
PACEMAKERS AND ICDs 1273
Fig.1.Examplesofantibradycardiapacing
modes. (A) Atrial-inhibited (AAI) pacing
for sinus arrest or bradycardia. The pulse
generatorisshownwithatrialleadsonly.
Theatriumispaced,unlesspacingisinhib-
itedbysensedspontaneousatrialdepolar-
izations. (B) Ventricular-inhibited (VVI)
pacing for atrioventricular (AV) heart
block (AVHB) with atrial fibrillation. The
pulsegeneratorisshownwithventricular
leads only. The ventricle is paced, unless
pacingisinhibitedbysensedspontaneous
ventricular depolarizations. (C) Ventricu-
lar-inhibited,atrial-triggered(VDD)pacing
forAVHBwithnormalsinoatrial(SA)node
andatrialfunction.Thepulsegeneratoris
attached to atrial leads for sensing only
and to ventricular leads for pacing and sensing. If a spontaneous atrial depolarization is sensed, the ventricle is paced after an
appropriateatrioventricularintervaltopermitventricularfilling.Thisistheatrial-triggeredventricularpacing(VAT)componentof
theVDDmode,whichalsoincludescapabilitiesoftheVVImode.(D)Dual-chambersequentialoratrioventricularuniversal(DDD)
pacing for sinus bradycardia and AVHB. The pulse generator is shown attached to atrial and ventricular leads for dual-chamber
sensingandpacing.ThismodeincorporatesAAI,VVI,andVATpacingcapabilities.ReprintedwithpermissionfromBernsteinAD,
Parsonnet V: Fundamentals of antibradycardia-pacemaker timing. ACC Educational Highlights 1995; 11:5–9; copyright American
CollegeofCardiology.
Device Design and Function Electrophysiology–British Pacing and Electrophysiology
Pacemaker Design and Function. Pacemakers are Group (NASPE/BPEG) pacemaker code (sometimes
powered by lithium-iodide batteries, with an expected called NBG code; table 9) is used as shorthand to de-
servicelifeof5–12yr,dependingondevicecapabilities. scribe pacing modes.137
Actual service life will depend on the need for pacing Timing Design: Single-chamber Pacemakers. To-
andtheprogrammedstimulusparameters.Mostsystems day, most pacemakers in the United States are conven-
use bipolar transvenous leads. These are positioned un- tional or adaptive-rate, dual-chamber devices.10 How-
der fluoroscopic guidance, with the lead configuration ever, with normal atrioventricular conduction and sinus
programmable (above). A single-chamber pacemaker node function, they may operate as single-chamber de-
stimulates the atria or ventricles on the basis of pro- vices, in the AAI/AAIR or VVI/VVIR modes, depicted in
grammedtimingintervals.Inaddition,bysensingintrin- figure 1. They have a single timing interval, the interval
sic atrial and/or ventricular depolarizations, it can be betweenstimuliintheabsenceofsenseddepolarization.
inhibited from providing unnecessary or inappropriate For single-chamber pacing modes, this interval is the
stimuli. Dual-chamber devices also time delivery of ven- atrial or ventricular escape interval. It is inversely
tricularstimulirelativetosensedatrialdepolarizationsto proportional to the pacing rate in paced pulses per
maintain proper atrioventricular synchrony. In figure 1, minute (ppm):
we illustrate how a pacemaker might be configured to
Escape interval (ms) 5 60,000/rate (ppm)
pace in patients with sinus node dysfunction or AVHB.
Throughout the remainder of the current article and in In the AAI mode (fig. 2), pacing will occur at the end
the sequel, the North American Society for Pacing and of the programmed atrial escape interval, unless a spon-
Table9.TheNASPE-BPEGGeneric(NBG)PacemakerCode
I II III IV V
Responseto Programmability/Rate Antitachycardia
ChamberPaced ChamberSensed SensedEvent Response* Functions†
O(none) O(none) O(none) O(none) O(none
A(atrium) A(atrium) I(inhibit) R(adaptiverate) P(ATP)
V(ventricle) V(ventricle) T(triggered) P(simpleprogrammable) S(shock)
D(dual:A1V) D(dual:A1V) D(IandT) M(multiprogrammable) D(dual:P1S)
S(single)‡ S(single)‡ C(communicating)
*Incurrentterminology,onlytheadaptiverateresponse(R)isindicatedbythefourthposition;allcurrentpacemakershavefullprogrammingandcommunicating
capability.Therefore,thelettersP,M,andCarenolongerused.
†ICDwithantibradycardiaandantitachycardiapacingcapabilities.
‡Single-chamberdevicethatpaceseithertheatriumorventricle.
ATP5antitachycardiapacing.
From Bernstein AD, Camm AJ, Fletcher RD, Gold RD, Rickards AF, Smyth NP, Spielman SR, Sutton R: The NASPE/BPEG generic pacemaker code for
antibradyarrhythmiaandadaptive-ratepacingandantitachyarrhythmiadevices.PacingClinElectrophysiol1987;10:794–9.Usedwithpermission.
Anesthesiology,V95,No5,Nov2001
1274 J. L. ATLEE AND A. D. BERNSTEIN
Fig.2.Depictionofatrial-inhibitedpacing,asforsinusbrady-
cardiawithintactatrioventricularconduction.Inthefirstbeat,
the atrium (A) is paced (by convention, an arrow pointing
toward the electrocardiogram [ECG] in the atrial timing dia-
gram).Theatrialrefractoryperiod(ARP)preventsconductedR
andensuingTwavesfrombeinginterpretedbythedeviceasa
Fig.4.Basictimingofadual-chamberpacemaker,withpacing
Pwaveandinappropriatelyresettingtheatrialescapeinterval
andsensinginbothchambers.Atrialandventricularstimuliare
(AA).AftertheprogrammedAAinterval,anotheratrialstimulus
shown in the timing diagrams by arrows pointing toward the
occursandresetstheinterval.Inthethirdbeat,aspontaneous
electrocardiogram (ECG) from above and below, respectively.
Pwaveissensed(byconvention,anarrowpointingawayfrom
The programmed atrioventricular (AV) interval provides time
theelectrocardiogramintheatrialtimingdiagram)beforethe
for ventricular filling. The atrial channel is refractory during
AAintervaltimesout.ThisresetstheAAintervalwithoutpacing
theatrioventricularintervalandfromdeliveryoftheventricu-
(theshortverticallineintheatrialtimingdiagramshowswhere
lar stimulus until the end of the programmed postventricular
the stimulus would have occurred). In the absence of further
atrial refractory period (PVARP). This prevents atrial sensing
sensing, the atrium is paced in the fourth beat when the AA
fromresettingtheescapetiming.Theblankingperiod(ventric-
interval times out. This example illustrates a principle that is
ularchannel)preventssensingoftheatrialstimulus.However,
usefulforinterpretingasingle-chamberpacemakerelectrocar-
sensing in the alert period after the blanking period would
diogram.Oncetheescapeintervalisknown(fromtheclinical
enableaspontaneousRwavetoresettheintervalbetweenthe
records, device telemetry, or measurement between consecu-
ventricular stimulus or sensed spontaneous R wave and the
tive paced beats), electrocardiographic interpretation is facili-
subsequentatrialstimulus(theVAinterval),therebyinhibiting
tatedbyworkingbackwardfromthelaststimulustoidentifythe
ventricular stimulation. As shown, this does not occur, so the
sensed event that reset the pacemaker’s escape timing as a P
atrioventricularintervaltimesoutwithdeliveryofaventricular
wave(orRwave,asthecasemaybe),andnotaspurioussignal.
stimulus. The ventricular refractory period (VRP) prevents
Reprinted with permission from Bernstein AD, Parsonnet V:
sensedTwavesfrominappropriatelyresettingtheVAinterval.
Fundamentalsofantibradycardia-pacemakertiming.ACCEdu-
SensingduringthealertperiodsafterthePVARPandVRPwill
cationalHighlights1995;11:5–9;copyrightAmericanCollegeof
resetbasictiming,initiatingnewatrioventricularandVAinter-
Cardiology.
vals, respectively. Reprinted with permission from Bernstein
AD, Parsonnet V: Fundamentals of antibradycardia-pacemaker
taneousatrialdepolarizationissensedfirstandresetsthe timing. ACC Educational Highlights 1995; 11:5–9; copyright
interval. Stimulus timing is identical for the VVI mode AmericanCollegeofCardiology.
(fig. 3). Ventricular pacing will occur at the end of the
atriumortheventricle.Inaddition,somesingle-chamber
ventricularescapeinterval,unlessaspontaneousventric-
pacemakers offer rate hysteresis as a programmable op-
ulardepolarizationissensedfirstandresetstheinterval.
tion. With this, the atrial or ventricular escape interval
Because of this timing similarity, some single-chamber
after a sensed depolarization is longer than that after a
pacemakers can be used with pacing leads in either the
paced depolarization. Rate hysteresis encourages the
emergence of an intrinsic rhythm, thereby reducing the
likelihoodofcompetitionbetweenpacedandspontane-
ous rhythm and prolonging battery life.
Timing Design: Dual-chamber Pacemakers. Fig-
ure 4 illustrates the basic timing design of a dual-cham-
ber pacemaker that can pace and sense in both the
atriumandtheventricle.Dual-chamberpacemakershave
two basic timing intervals, whose sum is the pacing-
cycle duration. The first is the atrioventricular interval,
Fig.3.Depictionofventricular-inhibitedpacing,asforatrioven- which is the programmed interval from a paced or
tricularheartblockwithatrialfibrillation.Inthefirstbeat,the
sensed atrial depolarization to the subsequent ventricu-
ventricle (V) is paced. The pacemaker’s ventricular refractory
period (VRP) prevents the ensuing T wave from being inter- lar stimulus. Some dual-chamber pacemakers offer the
pretedasanRwaveandinappropriatelyresettingtheventric- option of programmable atrioventricular interval hyster-
ular escape interval (VV). The programmed VV interval times
esis. If so, the atrioventricular interval after an atrial
out with delivery of a ventricular stimulus and resets the VV
interval.However,aspontaneousRwave(thirdbeat)issensed stimulus is longer than that following a sensed sponta-
before this times out. It inhibits the ventricular stimulus that neous P wave to maintain a uniform interval between
would have occurred (short vertical line in the ventricular-
atrial and ventricular contractions. The second basic
channel timing diagram) and resets the VV interval. With no
furthersensing,pacingoccurswhentheVVintervaltimesout timingintervalistheVAinterval,theintervalbetweena
(fourthbeat).ECG5electrocardiogram.Reprintedwithpermis- ventricular stimulus or sensed spontaneous R wave and
sionfromBernsteinAD,ParsonnetV:Fundamentalsofantibra-
the subsequent atrial stimulus. During the pacemaker’s
dycardia-pacemaker timing. ACC Educational Highlights 1995;
11:5–9;copyrightAmericanCollegeofCardiology. atrial and ventricular refractory periods (fig. 4), sensed
Anesthesiology,V95,No5,Nov2001