as second or third degree AV block, prolonged HV interval, AV ... block or PR 2 24 ms, was 8.4% corresponding to an annual in- cidence of 3%. In another ..... PR > 220 ms. Abbreviations: AV = atrioventricular; RBBB = right bundle-branch.
:]in. Cardiol. 16, 339-343 (1993)
= ~lectrophysiology, Pacing, and Arrhythmia hk section edited by A. John Camm, M.D.,ER. C X , EA .C.C.
4AI Pacing Mode: When Is It Indicated and How Should It Be Achieved? )EMCMHENES K A ” I S ,
M.D.,W.D. AND A. JOHN CAMM, M.D.,F.R.C.P., F.A.C.C.
tpamnent of Cardiological Sciences, St. George’s Hospital Medical School, London, England
ummary:AAI pacing offers better hemodynamic charactertics than dualchamber pacing and is the optunal mode for pa-
ents with sick sinus syndrome without AV conduction disortrs. AAI pacing may be achieved by single-chamber atrial 3cing. by p m g m i n g a dualchamber pacemaker to the AAI lode, or by Programming a dualchamber pacemaker to DDD lode with a long AV delay. The annual incidence of AV block :velopment in patients with sick sinus syndrome is low, pmb~ l y1-5%, but there is no method of detecting patients immune - prone to future developmentof AV block. Chronotropicinmpetence is often present in patients with sick sinus synwne but the value of additional rate response is not yet f m ’ established. Our recommendations for the choice of the xirnai method of pacing are discussed.
compad with patients having received atrial or dualchamber pacemakers.” VVI pacing appears to be inappropriatein patients with sinus node dysfunction and, unless the patient is in established c h n i c atrial fibrillation,this mode should not be prescribed. Paroxysmal atrial tachyarrhythrmas are no longer considered as a contraindication for atrial (AAl) or dualchamber @DD or DDI) pacing since there is evidence that atrial pacing can actually prevent recurrent attacks of paroxysmal atrial fibrillation.“ The main therapeutic problem, therefore, in the management of patients with SSS and apparently normal atrioventricular(AV) conduction is whether an AAI system is all that is needed or whether a dualchamber unit is essential.
’
Atrial Versus Dual-Chamber Pacing .ey words: AAI pacing, sick sinus syndrome,AV block
Development of AV block
PathoIogy studies in patients with SSS have documented widespread fibrosis throughout the conduction system8 and it has even been suggested that SSS is an expression of pmgresIn symptomatic sick sinus syndrome (SSS) presenting with sion of a generalized disorder affecting the specialized conadycardia the atrium should be paced unless the patient is in duction system? The pvalence of high-grade AV-block in unrmanent atrial fibrillation.’ Although randomized, prospecselected patients with SSS ranges from 0 to 17%> Therate of ie comparisonsbetween pacing modes are not available? retprogression expressed,for instance, by the annual incidence of spective studies have also shown a higher incidence of corn AV block in SSS patients paced with AAI pacemakers varies icationsandmortalityamongpatients~wi~vvIpacing considerably among reported studies (Table I). In a review of 28 studies concerning 1395patients followed up for an average of 34 months? the o v e d prevalence of AV block, defined as second or third degree AV block, prolonged HV interval, AV nodal Wenckebach at rates I120beatdmin, bundle-branch block or PR 2 24 ms, was 8.4% corresponding to an annual incidence of 3%. In another review concemhg 1878 patients folldress for reprints: lowed for 36 months,I0the estimated annual incidence of AV block, defined as second- or thirddegnx AV block, was 0.65%. Katritsis, M.D. tpartment of Cardiological Sciences Although only half of the reviewed papers specified the incluGeorge’s Hospital Medical School sion criteria for AAI pacing in this latter review, the Wenckeanmer Terrace bach point (when indicated) varied betyeen 110 and 150 lndon SW17 ORE, England beadmin and had no prognostic significance in terms of rate of development of AV block. Three recent studies also conceived: November 1, 1992 xepted: January 20, 1993 firmeda low incidence of AV block in these patients. In an anal-
itduction
Clin. Cardiol. Vol. 16, April 1993
340
TABLE I Development of new AV block in SSS patients treated with AAI pacing Authors (ref.) I. Review studies sunon and Kenny (3)
Rosenqvist andobel(10) U. Recent original studies Santini et al. (4) Koleais et al. ( 11) Haywood er al. ( 13)
Studies reviewed
Patients reviewed
Mean follow-up (months)
28
1395
34
28*
1878
36
135 91 24
5 years?
33 11
AV-block clefinition
Estimated AV block annual incidence (%)
second- oc t k i d e g AV ~ ~block, prolongedHV interval,AV nodal Wenckebach at rates I 120 beats/min, complete bundle-branch block, PR1240ms Secondor third degree AV block
Seconddegreeblock Completeheart block Highdegree AV block requiring ventricular pacing
3
0.65
0.56
0.4 16
of reviewed studies in the two series up to 20%. Drug-related in 6 patients. Abbreviarions: AV = atrioventricular, SSS = sick sinus syndrome. a Overlap
ysis of 91 patients paced with AAI units and with Wenckebach rates >120 beats/& at implantation,only one (1.1%) developed complete AV block over 33 months (annual incidence of 0.4%) although the incidence of asymptomatic m d d e gree heart block is not clearly indicated in these patients.” In anotfierextensive study of 135patients with SSS and a t d pacing, followed for an average period of 5 years: seven patients developed spontaneous second-degree AV block which resolved after discontinuation of antiarhytiunic therapy (digitalis, verapamil, amiodarone) in six of the patients. Recently, Brandt ef a!l2 published the results of a 6O-month follow-up of 213 consecutive patients treated with atrial pacing for SSS. Second- or thirddegree AV block o c c d in approximately 1.8%of the patients per year and its incidencewas much grpater in patients with complete bundle-branch block or bifascicular block. PR interval prolongation (200-240 ms) was not a usefulpredictorof subsequent AV block, whereas all patients with this complication had a Wenckebach point exceeding 130imp u l d m i n . By definition, however, all patients included in the study had Wenckebach points exceeding 120impulses/min. In our series,4 of 24 patients with SSS and AAI pacing followed for an average of 11 months developed highdegreeAV block requiring revision of the system and 1 further patient developed asymptomaticseconddegm AV block” Ofthe four patients with AV block only one had a Wenckebach rate less than 120 beats/min and the remainder demonstrated a mean Wenckebach rate of 143 beadmin. Thus, this study demonsfrated alackof Prognostic siflcanceofthe AV nodalWenckebach point as a predictor of future development of AV conduction distuhanm. In addition, it detected a higher risk for development of AV conduction disorders, althought klimited number of our patients invalidates any generalization of the findings. Electrophysiologicassessment before implantation does not seem particularly reliable in indicating patients immune to f u t w AV-block development. In another study,14a 25-
month follow-up of 43 patients with atrial pacing for SSS and normalAV conduction up to 130 beats/& found one patient to have been converted to a DDD unit, wheatas seven more patients demonstrated unspecified “deterioration” of AV conduction not necessitating revision of the pacemaker. The annual incidenceof AV-block development in SSS patients is therefore still debated and is probably highly dependent on the study population. Between 1 and 5% might be a good approximation,although scientificdocumentationis still inadequate. Unfortunately, the relation between the develop ment of AV block and factors such as the underlying disease and,in particular,the age of the patient is not clear. Reliable criteria or tests for the selection of patients prone to develop AV conduction disease do not exist. Drugs impairing conductionin the His-Purkinje system may reveal reducedcon duction reserve and such tests have been pmposed for the assessment of AV conduction, particularly in the presence of pexisting defects such as bifascicular block15In the disopyramide test16(2 mg/kg IV over 5 min), a positive result is the induction of second- or thirddegree intra- or infrahisian block andafter subsequent atrial peeing. The~enduring sin~~hythm sitivity of the test is further irxxeased if the HV interval exceeds 70 ms. A positive diqyrarnide test has been claimed to have a predictive value of 80% for subsequent development of Av block in patients with bifascicularblock procainamide (up to 10mg/kg) has also been used as a provocative test for patients with bifascicular block and history of syncope. l7 If h i g h 4 e p block is provoked, there is a chance of approximately 44% that thepatient will developcomplete heart block Ajmaline which briefly depresses intraventridar conducrion may also p v d e distal conduction block in patients with latent bundle-bmch block A positive response m i s t sof the development of s p taneousor atrial pacing-indud infrahisianblock18and canis an 83%risk of subsequent development of AV block, while a negative test canies a 1.6% risk for progression of conduction
D. Katritsis and A.J. Camm: AAI pacing mode d j w . Lafge-de trials With these tests are not available and,
for clinical applications,the predictive value of drugs for this pu'pose should be considered to be unknown. Consequently, their use for the identification of patients with currently n d AV conduction who are likely to develop AV conduction dist&mces in the future is not justified. Electrophysiologicalvariables such as the HV interval have been identified as possible predictors of complete heart block in patients with fascicular disea~e,but there exists considerable &bate about their truepedlctive value.19Sirmlady, the Wenckebath block cycle length has failed to detect patients immune to fumdevelopmentof AV block. However, a low Wenckebach pint, for example less than 120 impulses/min, argues against h e use of an AAI unit simply because of functional reasons, hat is, inappropriate AV intervalsat high pacing rates.
Hernodynamics Although both AAI and DDD modes are Collsidered as physiologic methodsof pacing compared with the VVI mode,they produce abnormal patterns of atrial and ventricular contraction. pacing from the right atrial appendage as it happens with both DDD and AAI modes can result in nonphysiological left heart AV intervals.20Atrial pacing, however, offers better hemodynamic characteristicsand improved cardiac output compared with dualchamberpacing?'-= Abnormal ventricular activation such as in patients With left bundle-branch block has been clearly shown to result in worse left ventricular function.24 Impavedsystolic thickening and augmented intramyocardialpressure associatedwith dus abnormal activation pattern have been shown to result in perfusion abnormalities in the septum.',26 Similarly,electrical stimulation of the right ventricle, especially from locations such as the ventricular apex, results in asynchronousventricularcontraction which depresses ventricular f u n c t i ~ n . ~ 'An~ association of congestive heart failure with VVI pacing has been clearly shown.I Histological abnormalities have been demonstrated in the myocardium of young patients with congenital heat block treated with VVI pacing.)O Experimental studies have also shown that transepicardialseptal ventricularpacing prevents histological changeswhich were induced by conventional apical pacing in the caninemyocardium,3' and septal His-Purkinje pacing is currently under evaluation in animals.32Further studies using intracardiac electrogramsand multigated nuclear acquisition imaging clearly demonstrated abnormal biventricular activation and contraction patterns in the apical-paced gr0up.3~ Ahid pacing, therefore, although not a substitutefor n d sinus nodal activity, is clearly superiorto dualchamber pacing in this respect (Table II). --Chamber
34 1
TABLE II Pacing mode characteristics ~
Atrialdependent AV synchny AAI AAIR
DDI DDIR DDD DDDR
+ + +/+/ -
+
+
rate adaptation
Atrialindependent rate adaptation -
+
-
-
+ +
-
Normal ventricular activation
+ +
+
-
+
4+I-
Abbreviations: AV = atrioventricular
tion following atrial pacing. Different AV intervals after a paced or sensedP wave, available in some modem units,a~ also useful in this setting. l b o potential problems should be considered with a long AV delay. First, prolonged AV delays impose a restriction on the upper rate limit provided by DDD units and reprogramming is needed if progression of AV disease results in continuous dualchamber pacing. A solution to thisproblem has been proposed by a new pacemaker model, in which there is a prolonged AV interval enablingatrial pacing without ventricular pacing. However, o m AV CondLlctiOn has been lost for a single beat and ventricularpacing has intervened, a second AV delay is instituted with C O n t i n ~ o A uV ~ pacing until AV conduction has returned and the cycle begins again. Second,with any pacemaker which tracks atrial activity, pacemaker-mediated tachycardia or the so-called AV desynchnization arrhythrma (i.e., unsensed retrograde P waves followed by ineffectual atrial stimulationduring atrial refractoriness3) may occurwhen retmgmde conduction is present Theiroccurrence is facilitatedby long AV delays or short postventricularatrial reftactory periods.Modern dualchamber units utilize algorithmswhich increase the postvenmcular atrial reli-actory period ortenninatepacemaker-mediatedtachycadiasbutcannotmm-
pletely eliminate their occurrence. Thus, in the presence of a long ~tmgradeconduction time,a dualchamberunit might be less ideal than an atrial pacemaker. A dualchamberunit programmed to the AAI mode probably offers an ideal alternative,but at the expenseof an additional lead and extra costs.Obviously, cost consi&ratim cannot dictate the choice of the pacemaker mode, but in the current situation of worldwide health care fiscal mnshaints they should be taken into account. We believe that most centers cannot afford to implant DDD units in order to program them to AAI when the same mode can be obtained with one lead only and at the cost of a simple WI pacemaker.
Atrial Pacing
Mortality A Itasonable way to avoid unnecessary ventricular stimula-
tion while retaining the benefits of ventricular pacing backup is the use of DDD units programmed to maximum AV delay. An AV delay of 250 to 300 ms (available in several DDD units) should maximize the likelihood of normal ventricular activa-
In patients with sinus node disease,prospective studies comparing the mmhty associated with AAI pacing and with DDD pacing do not exist. Retrospective studies indicate a higher incidence of mortality with W I compared with AAI and DDD
342
Clin. Cardiol. Vol. 16, April 1993
pacing,‘ although not in~ariably.~~ Santini et aL4in a recent analysis of 339 patients with SSS followed for an average of 5 years, demonstrated significantly less o v e d mortality with the DDD (16%)and AAI (13%) modes compared with the VVI mode (30%).Cardiac mortality was significantly higher in h e VVI group (13%)compared with the AAI group (3%), but not compared with the DDD group (6%).These observations, although not conclusiveas they are mainly limited by their retrospective nature and the probability of bias in pacing mode selection? suggest that AAI pacing might offer better survival compared with DDD pacing in patients less than 70 years old.
TABLE III Indications for the choice of the optlmal method of pacing in patients with sick sinus syndrome without permanent atrial fibrillation
-
Single chamber AAI Dual chamber AAImode
DDD with long AV delay DDD
Complicatim and Mode Survival
A dualchamber unit has a greater possibility for lead-associated complications such as thrombosis and lead failures. Failure rates for silicone and polyurethane leads have been reported to be 4 and lO%,respectively, over a 5-year follow-up.” Dualcharnber pacing, therefore, has a greaterpotential for developing future problems compared with AAI pacing. In a recent extensive study on the DDD mode survival?’ development of atrial fibrillation and loss of amal sensing appear to be the main reasons for reprogramming DDD pacemakers: AAI mode, therefore, is not expected to be different in this respect. Pacemaker-mediatedtachycardia, which can be avoided by AAI pacing, was responsible for 1% of reprogrammed DDD cases in the same study.
AAIR Versus DDDR Pacing Approximately one-thirdof the patients with sinus node disease are unable to achieve a maximum rate of 120 beadmin during maximal physical exercise.3g40The prevalenceof spe-
cific atrial chronotropic incompetence is estimated h m 2539 to 64%in elderly patiema Although AAIR pacing, compared with AAI pacing, has been shown to improve exercise capacity’” and decrease lactate production 42 in patients with SSS, not all studies agree. In a crossover study of 30 patients who had received AAIR pacing systems for SSS, we failed to detect any significant difference in exercise capacity between the “AAIand AAIR modes even in patients clearly demonstrating chronotropic inc~mpetence.~~ In addition, we could not detect any significant elimination of atrial ectopic a~tivity.4~ In patients paced in the AAIR mode, the PR shortening during exercise may be mpaud, resulting in a progressive incmse of the stimulus-RRRratio during exertion. As a consequence, the P wave progressively encroaches upon the preceding R wave, thus losing the hemodynamic contribution of atrial systole and resulting in the so-called “AAI pacemaker syndrome.”dl. 45 In a recent study of 17 patients paced with AAIR units for SSS and atrial chnotropic incompetence and normal AV conduction (defined as Wenckebach more than 120 beats/ min and HV 4 5 ms), Mabo et aL4 found 11 patients without normal adaptation of the stimulus-RRR ratio. In five of these patients P waves occurred immediately after or almost within the preceding R wave and two complained of exercise-related
No conduction abnormality Acquired RBBB Bifascicular block Wenckebach 220 ms Seconddegree AV block Thirddegvx AV block
Abbreviations:AV = atrioventricular;RBBB = right bundle-branch
block.
symptoms suggestive of pacemaker syndrome. Concomitant heart disease (such as a denervated transplanted heart), beta blockers, and class I antibytIuruc drugs were among the principal factors related to this failureof PR interval adaptation. We believe that precise indications as well as possible benefits of AAIR and DDDR modes have not yet been established and require further investigation. However, in patients with significant chronotmpic incompetence, the DDDR mode probably is the most reasonable choice.
conclusions AAI is the optimal mode for patients with sick sinus syndrome without AV-conduction disorders. AAI pacing may be achieved by single-chamberatrial pacing, by programming a dualchamber pacemaker to the AAI mode, or by pgamming a dualchamber pacemaker to DDD mode with a long AV delay. The necessary testsfor the pxelmplantatim assessment of patients with sick sinus syndrome are 12-14 ECG, 24 h Holter monitoring, and exercise testing. During implantation (and at follow-up), the Wenckebach point may also be determined for functional rather than prognostic msons, as previously discussed.Our recommendations for the choice of the optimal method of pacing are presented in Table Ill. Chronotropic incompetence is often present in patients with sick sinus syndrome. Additional rate response seem to be appropriatein such cases, but its value is not yet established.
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