Clin. Cardiol. 14. 257-260 (1991)
VVIR or DDD(R): Does it Matter? JtKKY
c. GRIFFIN. M D
Departiiient of Medicine and the Cardiovascular Research Institute, University of California, San Francisco, California, U S A
Key words: attificial cardiac pacing, ventricular pacing, atrial pucing, dual chamberpacing, hemodynamics, rate moclulated pacing
Introduction Both single and dual-chamber pacemakers with or without a sensor for rate modulation are now readily available. These pacemakers differ in price and complexity, but, more important, in the extent to which they restore cardiac rhythm in patients with a variety of symptomatic bradycardias. The accuracy with which sensor systems detect the occurrence and intensity of exercise is an important issue. I This brief review, however, will focus on the qucstions: ( I ) Does AV synchrony matter, and ( 2 ) Is VVIR pacing equivalent to AV synchronous pacing (DDD or DDDR)?
How 110 VVIR and DDD(R) Modes Compare with VVI? Dual-chamber or atrial pacing provides both atrioventricular (AV) synchrony and rate responsiveness if the patienl’s sinus node function is normal or if a sensor system is used (DDDR). These modes of pacing produce considerable improvements in hemodynamic variables, ex-
Addrehs lor reprinth: Jerry c‘. Griffin. M.D. Dep;inmcnt of Medicine and the Cardiovahcular Research Institute UCSF-Moftitt Hospital, Room 3 I 2 Box 0 2 I4 San Fr;uicisco. CA 94143
Received October 22, 1990 Acccptctl. Octohcr 26, 1990
ercise capacity,2-* and subjective measures of well beings,9,10 when compared with fixed-rate single-chamber pacing. The benefits of ventricular, single-chamber sensorbased, rate-modulating pacemakers (VVIR) are also impressive when compared with their single-chamber fixedrate counterparts (VVI). Thus both systems appear to be superior to fixed-rate ventricular devices.
How do the Various Modes Affect Ventricular Function? There are complex interrelationships among cardiac rate. AV synchrony, and left ventricular systolic and diastolic function. AV synchrony enhances ventricular filling while minimizing mean atrial and pulmonary venous pressure^,'^ coordinates AV valve closure, and minimizes regurgitation. I s The atrial contribution to cardiac output at rest is greatest in those patients with normal filling pressures and no congestive heart failure and least marked in those patients with abnormal filling pressures due to congestive heart failure.19 Although its magnitude is known, we do not know the importance of the atrial contribution in patients with very little cardiac reserve. Atrial contribution varies with rate, increasing as diastole shortens.20The contributions of the atria during exercise have not been studied directly; but in subjects with good left ventricular systolic function, the loss of atrial synchrony is compensated for by an increase in ejection fraction.*I The way in which the atria are uncoupled also may be important. Retrograde atrial activation may have different hetnodynamic consequences than AV block and random coupling or atrial fibrillation. With persistent retrograde atrial activation, the atria may propel blood away from the ventricles.20 Symptoms of “pacemaker syndrome” are usually seen at rest. It occurs in its fullest manifestation in 5 to 10%. of patients receiving VVI pacemakers and is usually associated with retrograde atrial activation.21,22Whether the exact mechanism involves mitral regurgitation, decreased left ventricular filling, and/or left atrial reflexes is not k n ~ w n . ~It” is . ~clear ~ that in patients with “pacemaker syndrome,” the maintenance of AV synchrony is criti-
2%
C l i n . Cardiol. Vol. 14, M d r c h 1991
cal. Symptoms are usually those of dizziness or even syncope, frcqucntly pounding, or fullness in the chest or throat. More subtle symptoms may occur in a much larger traction of patients with ventricular pacemakers. Stone and colleague^^^ found many fewer symptoms in patients receiving DVI pacemakers compared with those paced with VVI devices. Although VVI pacing controlled sympt o m requiring a pacemaker (most frequently syncope), other less specific symptoms tended to persist. Thus, exercise benefit is only one consideration, provision for AV synchrony at rest also may be of considerable importance. 2 5 If a lack of compliance restricts ventricular filling, the iibility to increase stroke volume may be diminished. In those patients with dccreased ventricular compliance, the loss of A V synchrony may require a marked increase in mean lcft atrial pressure to maintain left ventricular filling. Patients with longstanding arterial hypertension, aortic outflow o bst ruct ion, and restrictive card ion1yo path y may have significant dependence o n AV synchrony even if rate responsiveness is preserved. Whether the loss of AV synchrony directly affects diastolic function is controversial. Using angiographic and pressure recordings, Litwin and found no difference bctwccn vcntricular and A V sequential pacing in an animal model. Rosenqvist et t i / . , 2 7 using radionuclide and echo Doppler techniques, found effects on diastolic function: however, these were most significant between a nomial and paced rhythm rather than synchronous versus nonsynchronous rhythms. I n the hypersensitive carotid sinus syndrome. cardiodepressor effects of carotid sinus stimulation are frequently accompanied by vasodepressor effects. In the face of diminished preload, additional bcnefit may be obtained by atrial synchrony.2s
Preliminary data from studies looking at short versus long AV delays are variable,32-3sbut in one study a subgroup of patients paced in DDD mode with a vcry short or n o AV delay had a significant decline in exercise functional capacity compared with their perforniancc with longer AV dclays.35
Does AV Synchrony Affect Patient Longevity? Previously , the choice of pacing mode has rellectcd our concern about patient symptoms and sense of well-being, or the hetnodynamic efficiency o f the resulting rhythm and its effects on functional capacity. Three recent studies have raised the question of whether pacing in certain modes improves patient survival. Though retrospcctivc and not randomized, the issue is so important and the results so provocative that these studies must be given serious attention. More important, they must either be confimietl or refuted by prospective trials. Alpert and colleagues3') examined their results in patients receiving pacemakers for sinus node dysfunction. DVI or DDD pacemakers improved survival in those with lefi ventricular dyshnction. Rosenqvist and associate^^^.^^ compared thc results of pacing in two hospitals. One used only VVI pacing and the other used AAI whcnever possible. They selectcd a study population from the first hospital's total VVI population using the same criteria the second hospital employed to select patients for AAI pacing. Those patients receiving AAI pacemakers had iinproved survival, less congestive heart failure, and a lower probability of developing persistent atrial fibrillation (Fig. I ) . Feucr ~t t i / . 39 found a similar reduction in the devclopnient of atrial fibrillation between patients paced DDD and VVI. Sasaki rt M / . ~ O reported similar findings
Are There Direct Comparisons of VVIR and DDD Modes of Pacing? YOSurvival & Previous studies compared the contributions of atrial synchrony and rate rcsponsivcness to exercise-induced changes in cardiac output or exercise tolcrance. ConcluAAI 00s sions from these short-temi studies minimize the importance of AV synchrony and suggest that an increase in cardiac rate is the inore significant factor i n providing an AAI EXP WI 00s incrcnscd cardiac output with e x c r c i ~ e Of . ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ course, these findings were generated mostly from popuWIEXP lations of patients with AV block and noiinal left vcntricular function and may be misleading if applied to the cntire spccttum of pacemaker recipients. since left ventricular function ranges from nornial to highly impaired. It may 6 18 30 42 54 66 78 90 Months be that as left vcntricular dysfunction (eithcr systolic or Ftci I Acttiarial Lurvival I S presented lor 4 patient grotips. diastolic) increases. the need for an optimal pacing sys-=actual stirviviils lor patients receiving A A I ( A A I OBS) and tem increases as well. V V I ( V V I OBS) pacemakers. - - - - - =survival r i i t e ~expected t o r ;i N o onc has dircctly asscsscd the impact of persistent cohort of the gcneral population (Sweden) matched to the A A I ( A A I retrograde conduction on hemodynamics during ratcEXP) and V V I ( V V I EXP) pacemaker recipients. From Ref. 37. responsive single-chamber ventricular pacing (VVIR). Reproduced with perniission.
..
T
J . C. Griffin: VVl R o r DDD(R): Does it matter?
in patients with sinus node dysfunction. Among their patients paced with AAI or DDD system they observed fewer conrplications. particularly atrial fibrillation and thromboemhrlisiri. Although the actuarial survival rates were not dif'ferent. 5 of 6 deaths i n the VVI group were from cardiovasculitr causes in contrast to 0 of 3 in the AAI/DDD group. It is important to recognize that these studies were retrospcctive and do not elucidate the mechanism by which inipro\wd survival was achieved. It is unlikely to be rate response to exercise since. among the patients showing benet'it, all in the study by Rosenqvist and some in the studies of Alpert and Sasaki were paced with fixed rate systems. Other factors. alone or in combination, were probably responsible. the most likely being AV synchrony (AAL. DVI. or DDD) andlor a normal ventricular contract ion pat re m ( AA I). 27. I, 4 2
Sum ma ry A continuing emphasis on cost effectiveness in health care may require that we use more expensive pacing system$ orily in situations where there is clear medical and scientific evidence of increased efficacy. Although dualchunibcr and/or sensor-based, rate-modulating pacing systems are electronically no less reliable, they are part of a more complex pacing system. The requirement for two leads. one of which must maintain both pacing and sensing in thc atrium, will inevitably impact the cost and reliability of such systems coinpared with a single-chamber ventricular system. Yet, there is clear evidence that AV synchrony is important at rest, particularly in patients susceptible to pacemaker syndrome, and there is mounting evidcncc that AV synchrony during exercise is beneficial indepctident of rate response. Finally. and perhaps most impomnt. there is the suggestion that patient longevity may be extended by using pacing systems that preserve AV synchrony and/or minimize ventricular pacing.
References I.
2. 3.
4.
5.
C-P, Mchta D. Toff WD. Stott RJ. Ward DE. Camm AJ: I .imitations of ratc response o f an activity-sensing ratercqmisive pacemaker t o diffcrcnt fi)rnis o f activity. PACE I I . 141-1so (1988) K;irlof I: Hcmodynaniic cl'l'cct of atriiil triggered versus fixed rate pacing ;it rest and during exercise in complete heart block. ,4c,/(! Mtd S t ~ r ~ 197. t l I95 (1975) Kiusc I. Arnnian K. Conradson RB, Ryden L: A comparison of tlic acutc and long-term hernodynamic effects of ventricular iiihibited and atrial synchr(rnous ventricular inhibited pacing. ( ' / r ~ ~ u l ~ i /65. i o t l 846 (1982) 1;;inanapaiir L. Bennett DH. Monks P: Atrial synchronized vciitricu1:ir pacing: Contribution of the chronotropic response tn iniprovcd exercise pcrfoiiiiance, f A ( ' E 6 , 601 (I983) Pcilins EJ. Morley CA. Chan SL. Sutton R: Randomized controlled trial ol'physiological and Ventricular pacing. Br Heor/ ./ so. I12 (1983) I.ati
259
6 . Kristcnsson B-E, Krister A, Smedgard P, Rydcn L: Physiological versus single-rate ventricular pacing: A double-blind crnss-over study. PACE 8. 73 (1085) 7. Pehrsson SK. Hjenidahl P , Nordlander R, Astrom H: A c o n parison of synipathoadrenal activity and cardiac performance at rest and during exercise in patients with ventricular demand or atrial synchronous pacing. Br Hecirr J 60, 212-220 (1988) 8. Rcdiker DE, Eagle KA. Hoinma S, Gillam LD. Harthome JW: Clinical and hcmodynamic comparison of VVI versus DDD pacing in patients with DDD pacemakers. A m J Ctirtliol 61. 323-329 (1988) 9. Fronier M, Kappenberger L, Babotai I: Subjective and objcctive response to single- verbus dual-chamber pacing. J ElccrroptiJsiol 1 343-349 (1987) 10. Boon NA. Frcw AJ. Johnston JA, Cobbe SM: A comparison o f symptoms and intra-arterial ambulatory blood pressure tluring long-term dual chamber atrioventricular synchronous (DDD) and ventricular demand (VVI) pacing. Br H i w r J 58. 34-39 (1987) I I. Donaldson RM, Fox K, Rickards AF: Initial experience with a physiological. rate responsive pacemaker. Br MedJ286, 667 (1983) 12. Bcnditt DG. Mianulli M , Fetter J . Benson DW Jr. Dunnigan A, Molina E. Gomick CC. Almquist A: Single-chamber cardix pacing with activity-initiated chronotropic response: Evaltw tion by cardiopulmonary exercise testing. Circultrriori 75, I 84 (1987) 13. Smedgard P, Kristensson B-E, Kmsc I , Ryden L: Ratzresponsive pacing by nieans of activity sensing versus single rate ventricular pacing: A doublc-blind cross-over study. PACE 10, 902-915 (1987) 14. Faerestrand S, Breivik J , Ohm 0 - J : Assessment of the work capacity and relationship between rate response and exercise tolerance associated with activity-sensing rate-responsive veiltrictilar pacing. PACE 10, 1277-1290 (1987) 15. Buckingham TA. Woodruff RC, Pcnnington DG, Redd R M . Janosik DL. Labovitz AJ. Graves R, Kennedy HL: Effect of ventricular function on the exercise hernodynamics of variable rate pacing. J Am Coll Currliol I I , 1269-1277 (1988) 16. Trappe H-J. Klein H , Frank G , Lichtlen PR: Rate-responsive pacing as compared to tixed-rate VVI pacing in patients aftcr ablation of the atrioventricular conduction system. Eur Hiwrf .I 9. 642-648 (1988) 7. Braunwald E. Frahni CJ: Studies on Starling's law of the heart. Cirtu/~/iorr24. 633 ( I96 1 ) 8. Morgan DE, Norman R. West RO, Burggraf G: Echocardiographic asscssment ol' tricuspid regurgitation during vcntricular demand pacing. A m J Ctrrdiol 58. 1025 (1986) 9. Greenberg B. Chattcrjec K. Parnilcy WW, Werner J . Holly AN: The influence of left ventricular filling pressure on atrial contribution to cardiac output. Am Hetirt 598, 742-751 (1979) 20. Naito M , Dreifus LS. David D, Michelson EL, Mardelli J . Kmctzo JJ: Reevaluation of the role ofthe atrial systole t o cardac hemodynamics: For pulmonary vcnous regurgitation during abnomial atrioventricular sequencing. A m Heurr J 10.5. 295-302 (1983) 21. Ausubel K, Steingart RM, Shiinshi M , Klementowicz P. Furman S: Maintenance of exercise stroke volume during ventricular versus atrial synchronous pacing: Role of contractility. Cir.r n / t i / i o / i 72. 1037 (1985) 22. Cohen SI. Frank HA: Preservation of active atrial transport. An important clinical consideration in cardiac pacing. Clw.t/ 81, 51-54 (1982) 23. Alicandri C , Fouad FM. Tanzi RC, Castle L, Morant V: Three cases of hypotension and syncope with ventricular pacing: POSsible role of atrial reflexes. Arir J Crrrrliol42. 137-142 (1978)
.
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24. Stone JM, Bhakta RD, Lutgen J : Dual chamber sequential pacing management of sinus node dysfunction: Advantages over single-chamber pacing. Am Heurt J 104, 1319-1327 (1982) 25. Nishimura RA, Gersh BJ, Vlietstra RE, Osbom MJ. Ilstrup DM, Holmes DR Jr: Henlodynamic and symptomatic consequences of ventricular pacing PACE 5 , 903-908 (1982) 26. Litwin SE, Gorman G , Huang SK: Effects of different pacing modes on left ventricular relaxation in closed-chest dogs. PACE 12, 1070-1076 (1989) 27. Rosenqvist M, lsaaz K, Botvinick EH, Dae MW. Cockrell J . Abbott JA, Schiller NB, Griffin JC: The relative importance of activation sequence compared to atrioventricular synchrony in left ventricular function. Am J Curdiol. In press (1991) 28. Morley CA, Pemns EJ, Grant P, Chan SL, McBrien DJ, Sutton R: Carotid sinus syncope treated by pacing. Br Heurt J 47, 41 1-418 (1982) 29. Pehrsson SK: Influence of heart rate and atrioventricular synchronization on maximal work tolerance in patients treated with artificial pacemakers. A m Med Scurid 214, 3 I I (1983) 30. Kristensson B-E, Amman K , Ryden L: The haemodynamic importance of atrioventricular synchrony and rate increase at rest and during exercise. Eur Heurf J 6, 773 (1985) 31. Jutzy RV, lsaeff DM, Bansal RC, Florio J , Marsa RJ, Jutzy KR: Comparison of VVIR, DDD, and DDDR pacing. J Electropphysiol 3, 194-20 I ( I989) 32. Ryden L, Karlsson 0, Kristensson B-E: The importance of different atrioventricular intervals for exercise capacity. PACE I I , 10.5-I062 (1988) 33. Pearson AC, Janosik DL, Redd RR, Buckinghani TA, Blum RI, Labovitz AJ: Doppler echocardiographic asscssment of the effect of varying atrioventricular delay and pacemaker mode on left ventricular filling. Am Heurf J 11.5, 61 1-621 (1988) 34. Haskell RJ, French WJ: Physiological importance of different atrioventricular intervals to improved exercise performance in
35.
36.
37. 38. 39.
40.
41. 42.
patients with dual chamber pacemakers. Br Hetrr/ J 6 I , 46 -5 I (1989) Landzberg JS, Franklin JO, Mahawar SK, Hiinelinan RB, Botvinick EH, Schiller NB, Springer MJ, Griffin JC: Benefits o f physiologic atrioventricular synchronization for pacing with an exercise rate response. Am J Cardiol 66, 193-197 (1990) Alpert MA, Curtis JJ, Sanfelippo JF, Flaker GC, Walls JT. Mukerji F, Villareal D, Katti SK, Madigan NP, Morgan RJ: Comparative survival following permanent ventricular and dualchamber pacing for patients with chronic symptomatic sinus node dysfunction with and without congestive heart tiailurc. Arrr Heurf J 113, 958-965 (1987) Rosenqvist M , Brandt J , Schuller H: Long-term pacing in sinus node disease: Effects of stimulation mode on cardiovascular morbidity and mortality. Am Heurt J 1 16, 16-22 (19x8) Rosenqvist M, Brandt J , Schuller H: Atrial versus ventricular pacing in sinus node disease: A treatment comparison study. Am Heurt J 1 1 1 , 292 (1986) Feuer J M , Shandling AH, Messenger JC, with the technical assistance of Castellanet C D , Thomas LA: Influence of cardiac pacing mode on the long-term development o f atrial fibrillation. An7 J Curdiol 64, 1376-1379 (1989) Sasaki Y, Shiinotori M, Akahane K, Yonekura H, Hirano K , Endoh R, Koike S, Kawa S, Furuta S, Homma T: Long-temi follow-up of patients with sick sinus syndrome: A comparison of clinical aspects among unpaced, ventricular inhibited paced. and physiologically paced groups. PACE I I , 1575-1583 (1988) Zile MR, Blaustein AS, Shimizu G, Gaasch WH: Right ventricular pacing reduces the rate of leti ventricular relaxation and tilling. J Am Co// Curdiol 10, 702-709 (1987) Baller D, Wolpers H-G, Zipfel J , Bretschneider H-J, Hclligc (3: Comparison of the effects of right atrial, right vcntricular apex and atrioventricular sequential pacing on myocardial o x y gen consumption and cardiac efficiency: A laboratory investigation. PACE I I , 394-403 (1988)
VVIR or DDD(R): Does it Matter? JtKKY
c. GRIFFIN. M D
Departiiient of Medicine and the Cardiovascular Research Institute, University of California, San Francisco, California, U S A
Key words: attificial cardiac pacing, ventricular pacing, atrial pucing, dual chamberpacing, hemodynamics, rate moclulated pacing
Introduction Both single and dual-chamber pacemakers with or without a sensor for rate modulation are now readily available. These pacemakers differ in price and complexity, but, more important, in the extent to which they restore cardiac rhythm in patients with a variety of symptomatic bradycardias. The accuracy with which sensor systems detect the occurrence and intensity of exercise is an important issue. I This brief review, however, will focus on the qucstions: ( I ) Does AV synchrony matter, and ( 2 ) Is VVIR pacing equivalent to AV synchronous pacing (DDD or DDDR)?
How 110 VVIR and DDD(R) Modes Compare with VVI? Dual-chamber or atrial pacing provides both atrioventricular (AV) synchrony and rate responsiveness if the patienl’s sinus node function is normal or if a sensor system is used (DDDR). These modes of pacing produce considerable improvements in hemodynamic variables, ex-
Addrehs lor reprinth: Jerry c‘. Griffin. M.D. Dep;inmcnt of Medicine and the Cardiovahcular Research Institute UCSF-Moftitt Hospital, Room 3 I 2 Box 0 2 I4 San Fr;uicisco. CA 94143
Received October 22, 1990 Acccptctl. Octohcr 26, 1990
ercise capacity,2-* and subjective measures of well beings,9,10 when compared with fixed-rate single-chamber pacing. The benefits of ventricular, single-chamber sensorbased, rate-modulating pacemakers (VVIR) are also impressive when compared with their single-chamber fixedrate counterparts (VVI). Thus both systems appear to be superior to fixed-rate ventricular devices.
How do the Various Modes Affect Ventricular Function? There are complex interrelationships among cardiac rate. AV synchrony, and left ventricular systolic and diastolic function. AV synchrony enhances ventricular filling while minimizing mean atrial and pulmonary venous pressure^,'^ coordinates AV valve closure, and minimizes regurgitation. I s The atrial contribution to cardiac output at rest is greatest in those patients with normal filling pressures and no congestive heart failure and least marked in those patients with abnormal filling pressures due to congestive heart failure.19 Although its magnitude is known, we do not know the importance of the atrial contribution in patients with very little cardiac reserve. Atrial contribution varies with rate, increasing as diastole shortens.20The contributions of the atria during exercise have not been studied directly; but in subjects with good left ventricular systolic function, the loss of atrial synchrony is compensated for by an increase in ejection fraction.*I The way in which the atria are uncoupled also may be important. Retrograde atrial activation may have different hetnodynamic consequences than AV block and random coupling or atrial fibrillation. With persistent retrograde atrial activation, the atria may propel blood away from the ventricles.20 Symptoms of “pacemaker syndrome” are usually seen at rest. It occurs in its fullest manifestation in 5 to 10%. of patients receiving VVI pacemakers and is usually associated with retrograde atrial activation.21,22Whether the exact mechanism involves mitral regurgitation, decreased left ventricular filling, and/or left atrial reflexes is not k n ~ w n . ~It” is . ~clear ~ that in patients with “pacemaker syndrome,” the maintenance of AV synchrony is criti-
2%
C l i n . Cardiol. Vol. 14, M d r c h 1991
cal. Symptoms are usually those of dizziness or even syncope, frcqucntly pounding, or fullness in the chest or throat. More subtle symptoms may occur in a much larger traction of patients with ventricular pacemakers. Stone and colleague^^^ found many fewer symptoms in patients receiving DVI pacemakers compared with those paced with VVI devices. Although VVI pacing controlled sympt o m requiring a pacemaker (most frequently syncope), other less specific symptoms tended to persist. Thus, exercise benefit is only one consideration, provision for AV synchrony at rest also may be of considerable importance. 2 5 If a lack of compliance restricts ventricular filling, the iibility to increase stroke volume may be diminished. In those patients with dccreased ventricular compliance, the loss of A V synchrony may require a marked increase in mean lcft atrial pressure to maintain left ventricular filling. Patients with longstanding arterial hypertension, aortic outflow o bst ruct ion, and restrictive card ion1yo path y may have significant dependence o n AV synchrony even if rate responsiveness is preserved. Whether the loss of AV synchrony directly affects diastolic function is controversial. Using angiographic and pressure recordings, Litwin and found no difference bctwccn vcntricular and A V sequential pacing in an animal model. Rosenqvist et t i / . , 2 7 using radionuclide and echo Doppler techniques, found effects on diastolic function: however, these were most significant between a nomial and paced rhythm rather than synchronous versus nonsynchronous rhythms. I n the hypersensitive carotid sinus syndrome. cardiodepressor effects of carotid sinus stimulation are frequently accompanied by vasodepressor effects. In the face of diminished preload, additional bcnefit may be obtained by atrial synchrony.2s
Preliminary data from studies looking at short versus long AV delays are variable,32-3sbut in one study a subgroup of patients paced in DDD mode with a vcry short or n o AV delay had a significant decline in exercise functional capacity compared with their perforniancc with longer AV dclays.35
Does AV Synchrony Affect Patient Longevity? Previously , the choice of pacing mode has rellectcd our concern about patient symptoms and sense of well-being, or the hetnodynamic efficiency o f the resulting rhythm and its effects on functional capacity. Three recent studies have raised the question of whether pacing in certain modes improves patient survival. Though retrospcctivc and not randomized, the issue is so important and the results so provocative that these studies must be given serious attention. More important, they must either be confimietl or refuted by prospective trials. Alpert and colleagues3') examined their results in patients receiving pacemakers for sinus node dysfunction. DVI or DDD pacemakers improved survival in those with lefi ventricular dyshnction. Rosenqvist and associate^^^.^^ compared thc results of pacing in two hospitals. One used only VVI pacing and the other used AAI whcnever possible. They selectcd a study population from the first hospital's total VVI population using the same criteria the second hospital employed to select patients for AAI pacing. Those patients receiving AAI pacemakers had iinproved survival, less congestive heart failure, and a lower probability of developing persistent atrial fibrillation (Fig. I ) . Feucr ~t t i / . 39 found a similar reduction in the devclopnient of atrial fibrillation between patients paced DDD and VVI. Sasaki rt M / . ~ O reported similar findings
Are There Direct Comparisons of VVIR and DDD Modes of Pacing? YOSurvival & Previous studies compared the contributions of atrial synchrony and rate rcsponsivcness to exercise-induced changes in cardiac output or exercise tolcrance. ConcluAAI 00s sions from these short-temi studies minimize the importance of AV synchrony and suggest that an increase in cardiac rate is the inore significant factor i n providing an AAI EXP WI 00s incrcnscd cardiac output with e x c r c i ~ e Of . ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ course, these findings were generated mostly from popuWIEXP lations of patients with AV block and noiinal left vcntricular function and may be misleading if applied to the cntire spccttum of pacemaker recipients. since left ventricular function ranges from nornial to highly impaired. It may 6 18 30 42 54 66 78 90 Months be that as left vcntricular dysfunction (eithcr systolic or Ftci I Acttiarial Lurvival I S presented lor 4 patient grotips. diastolic) increases. the need for an optimal pacing sys-=actual stirviviils lor patients receiving A A I ( A A I OBS) and tem increases as well. V V I ( V V I OBS) pacemakers. - - - - - =survival r i i t e ~expected t o r ;i N o onc has dircctly asscsscd the impact of persistent cohort of the gcneral population (Sweden) matched to the A A I ( A A I retrograde conduction on hemodynamics during ratcEXP) and V V I ( V V I EXP) pacemaker recipients. From Ref. 37. responsive single-chamber ventricular pacing (VVIR). Reproduced with perniission.
..
T
J . C. Griffin: VVl R o r DDD(R): Does it matter?
in patients with sinus node dysfunction. Among their patients paced with AAI or DDD system they observed fewer conrplications. particularly atrial fibrillation and thromboemhrlisiri. Although the actuarial survival rates were not dif'ferent. 5 of 6 deaths i n the VVI group were from cardiovasculitr causes in contrast to 0 of 3 in the AAI/DDD group. It is important to recognize that these studies were retrospcctive and do not elucidate the mechanism by which inipro\wd survival was achieved. It is unlikely to be rate response to exercise since. among the patients showing benet'it, all in the study by Rosenqvist and some in the studies of Alpert and Sasaki were paced with fixed rate systems. Other factors. alone or in combination, were probably responsible. the most likely being AV synchrony (AAL. DVI. or DDD) andlor a normal ventricular contract ion pat re m ( AA I). 27. I, 4 2
Sum ma ry A continuing emphasis on cost effectiveness in health care may require that we use more expensive pacing system$ orily in situations where there is clear medical and scientific evidence of increased efficacy. Although dualchunibcr and/or sensor-based, rate-modulating pacing systems are electronically no less reliable, they are part of a more complex pacing system. The requirement for two leads. one of which must maintain both pacing and sensing in thc atrium, will inevitably impact the cost and reliability of such systems coinpared with a single-chamber ventricular system. Yet, there is clear evidence that AV synchrony is important at rest, particularly in patients susceptible to pacemaker syndrome, and there is mounting evidcncc that AV synchrony during exercise is beneficial indepctident of rate response. Finally. and perhaps most impomnt. there is the suggestion that patient longevity may be extended by using pacing systems that preserve AV synchrony and/or minimize ventricular pacing.
References I.
2. 3.
4.
5.
C-P, Mchta D. Toff WD. Stott RJ. Ward DE. Camm AJ: I .imitations of ratc response o f an activity-sensing ratercqmisive pacemaker t o diffcrcnt fi)rnis o f activity. PACE I I . 141-1so (1988) K;irlof I: Hcmodynaniic cl'l'cct of atriiil triggered versus fixed rate pacing ;it rest and during exercise in complete heart block. ,4c,/(! Mtd S t ~ r ~ 197. t l I95 (1975) Kiusc I. Arnnian K. Conradson RB, Ryden L: A comparison of tlic acutc and long-term hernodynamic effects of ventricular iiihibited and atrial synchr(rnous ventricular inhibited pacing. ( ' / r ~ ~ u l ~ i /65. i o t l 846 (1982) 1;;inanapaiir L. Bennett DH. Monks P: Atrial synchronized vciitricu1:ir pacing: Contribution of the chronotropic response tn iniprovcd exercise pcrfoiiiiance, f A ( ' E 6 , 601 (I983) Pcilins EJ. Morley CA. Chan SL. Sutton R: Randomized controlled trial ol'physiological and Ventricular pacing. Br Heor/ ./ so. I12 (1983) I.ati
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