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Physiological pacing for elderly patients: exploit the benefits but don't overdo it.

Permanent cardiac pacing was pioneered in 1958 by Elmqvist and Senning for the treatment of symptomatic bradycardia [1]. Although effective at preventing syncope and sudden death, these early systems were associated with serious problems. Generator failure, extrusion and infection together with electrode displacement and fracture were the more frequent mechanical ones. There were also problems with the technology; fixed-rate pacing for example could compete with the natural pacemaker resulting in ventricular tachycardia and occasionally fibrillation. The introduction of demand pacing in 1970 rendered fixed-rate pacing practically obsolete. Further evolution of pacemaker technology during the subsequent decade led to the introduction of dual-chamber pacing--often referred to as `physiological pacing'. The potential haemodynamic benefits of harnessing atrial contraction had been recognized some 20 years earlier but only recently has the technology become generally available [2]. Rather than a single transvenous electrode, a dual-chamber pacing system incorporates two electrodes which sense and pace the right atrium and ventricle respectively mimicking the natural sequence of chamber contraction.

What are the benefits of physiological pacing? In patients with complete heart block, physiological pacing improves a number of haemodynamic parameters. Compared with single-chamber ventricular pacing, stroke volume and cardiac output are increased and central filling pressures reduced [3]. These beneficial changes are reflected by improvements in treadmill time [4], maximum oxygen uptake and neuroendocrine markers; plasma atrial natriuretic peptide (ANP), a marker of both left and right atrial pressures, is reduced during physiological pacing [5] together with the level of circulating plasma noradrenalin--a marker of systemic sympathetic activation [6].

Physiological pacing also avoids symptoms due to `pacemaker syndrome' [7, 8]. The substrate for pacemaker syndrome is atrial contraction against closed atrioventricular valves (mitral and/or tricuspid) which can trigger a series of adverse haemodynamic and neurohumoral disturbances. As may be anticipated, patients with single-chamber ventricular pacemakers are most at risk--particularly those patients with intact ventriculoatrial conduction (when atria and ventricles contract together). A recent investigation suggested that symptoms consistent with pacemaker syndrome may be detected in over 80% of such patients [9]. Even in apparently asymptomatic patients with a single-chamber ventricular pacemaker, dual-chamber pacing may effect significant subjective and objective benefits which suggest a high level of `subclinical' pacemaker syndrome within the pacemaker population [10].

The availability of ever more sophisticated pacing systems has increased the costs of pacemaker implantation and follow-up and has caused some confusion as to which systems are the most appropriate for which patients. For example, until recently it had been generally assumed that the physiological benefits offered by the more sophisticated pacemakers were unnecessary and of marginal benefit to elderly patients [11]. The reasons are not clear but such a policy may have been a cryptic form of health care rationing [12]. These and related issues prompted the British Pacing and Electrophysiological Group (BPEG) to publish recommendations on the application of pacemaker technology [13]. In brief, BPEG stated that patients with advanced atrioventricular nodal disease (i.e. second and third degree heart block) and intact atrial activity should be considered for dual-chamber pacemakers. The working party recognized that there would be circumstances where insertion of a sophisticated system may be inappropriate, e.g. patients with terminal disease or severely limited by non-cardiac disease, but that age alone should not determine implantation policy. Only patients without organized atrial activity, i.e. atrial fibrillation or standstill, should be prescribed single-chamber ventricular pacemakers. In other words, a physiological system should be considered in all patients where technically possible.

It should be recognized that these recommendations were largely based on studies of patients aged less than 75 years; patients aged over 75 years of age have been, until lately, largely excluded from pacemaker studies. Can the working party recommendations be equally applied to patients aged over 75 years? Since these patients make up at least 60% of patients referred for pacemaker insertion, and at least 50% of them have advanced atrioventricular block (with or without associated sinoatrial disease), this is clearly an important issue [14]. There is no a priori reason why elderly patients should not stand to gain just as much from dual-chamber pacing as do younger patients. Indeed changes in the cardiovascular system with advancing age may render the elderly patient less tolerant of nonphysiological pacing. The left ventricle tends to become thicker, less compliant and increasingly dependent upon the contribution of atrial filling during late diastole [15]. Patients with overt left ventricular dysfunction, increasingly prevalent at later ages [16], tend to operate even higher on the Frank-Starling curve and are critically dependent on the contribution of atrial contraction to maintain left ventricular end-diastolic volume. In these patients loss of atrial contraction may precipitate congestive heart failure. Finally, corrective cardiovascular reflexes may be depressed with advanced age predisposing subjects to symptomatic hypotension and pacemaker syndrome.

A recent prospective study compared single-chamber ventricular pacing with dual-chamber pacing in elderly patients with complete heart block [17]. Although the sample was small (n = 16) and perhaps not entirely representative of those patients referred for consideration of pacemaker insertion, it was none the less the first study to compare DDD vs. VVI pacing specifically within an elderly group (> 75 years). Rather than measuring [MVO.sub.2] or treadmill performance, which have limited physiological relevance in an elderly population whose general activity level may be reduced, simple tests reflecting daily activities were performed; stand-ups from a chair, a 6-minute walk and time to climb a flight of stairs. There was a significant improvement in exercise and symptom scores in DDD compared with VVI pacing mode. These findings, although preliminary, are in accord with the observations of others [18] and serve to support the central tenet that it is no longer acceptable to withhold physiological pacing from patients with advanced atrioventricular block on the grounds of age alone [13].

But what of the costs of implanting physiological pacemakers into all patients with advanced atrioventricular block? Publication of the BPEG guidelines prompted some pacing centres to examine their implantation policy and the financial implications of the guidelines. de Belder et al. reported the experience of the South-West Thames regional pacing centre [12]. Four hundred and thirty-three patients received pacemakers during 1991 of whom some 61% were aged over 75 years. Two hundred and ninety-five patients (68%) had complete heart block either alone or in association with sinoatrial disease. Only 12% of patients received a dual-chamber system; 28% of patients under 75 years and 3% of patients over 75 years. Ray et al. reported the experience of the Northern Region [19]. During an 18-month period 550 pacemakers were inserted; 61% in patients with complete heart block either alone or in association with sinoatrial disease. During the final 6 months of the study period (following dissemination of BPEG guidelines) the majority (101/126) continued to receive VVI pacemakers--especially patients aged over 75 years.

One of the more likely explanations for the shortfall between the working party recommendations and reported practice may simply be the cost of DDD systems. Dual-chamber generators alone are at least twice as expensive as single-chamber generators and, of course, dual-chamber systems require an extra electrode. de Belder estimated that implantation of dual-chamber pacemakers in all suitable patients (i.e. those with advanced a-v block and sinus rhythm) aged over 75 years would have added 266315[pounds] to the regional pacing budget representing an increase of 49%. The authors concluded that wholesale implementation of the working party recommendations, without reservation, would have a tremendous impact on pacemaker budgets.

Aside from the expenditure on pacing hardware, there are additional covert expenses which are more difficult to evaluate. For example dual-chamber pacemaker implantation is generally more difficult and takes longer so increasing the risk of infection. Infection is a feared complication which often requires pacemaker explantation and insertion of a new system under intensive antibiotic cover. The atrial electrode may also become displaced in about 5% of cases requiring a corrective procedure. Finally dual-chamber pacemaker patients are usually required to re-attend the regional centre as the necessary programming technology and/or expertise may not be available locally. The Oxford regional pacing centre serves an extensive area with patients referred from as far afield as Gloucester and Northampton and the problems associated with transporting elderly patients and their relatives or carers may be considerable.

Although the costs of dual-chamber pacing may influence pacemaker prescription, there may be additional reasons for the apparent shortfall between BPEG guidelines and reported pacing practice. It may be argued that patients aged over 75 years constitute a selected group in whom the presence of advanced conduction disease may be a marker of an advanced ageing process. Within this population `limiting noncardiac disease or cognitive impairment' may not be uncommon and in such subjects physiological pacing would not be anticipated to improve the overall quality of life. In practice, these patients would be implanted with a single-chamber system. Precisely what proportion of patients aged over 75 years with advanced conducting disease are not considered for dual-chamber pacing on the grounds of `limiting noncardiac disease or cognitive impairment' is unclear at present. Within this same population there are also patients who would clearly stand to benefit from physiological pacing; determining which patients are likely to benefit remains a matter of clinical judgement and not necessarily one of policy. Petch was moved to comment that `. . . all the guidelines ignore patients and their clinical needs; the recommendations deal solely with conduction systems and their defects' [20]. These and related issues could be addressed by an audit of pacemaker implantation in regional centres. The results would establish baseline pacing practice and provide a realistic estimation of the financial implications of the working party guidelines--particularly that of appropriate pacemaker prescription for elderly patients. What is clear is that the reported estimations of the costs of pacemaker prescription for elderly people are almost certainly exaggerated and only serve to support outdated pacing practices.

Finally, over the past ten years there has been interest in so-called `rate-adaptive or responsive' pacemakers. Rather than pacing at a set demand rate (e.g. 72/min), these pacemakers can accelerate the heart rate in response to various physiological indicators of exercise. These indicators include minute volume, right ventricular pressure, derived QT interval, blood pH and temperature. The most widely used parameter is upper body movement which is detected by a sensor located in the generator itself. Upper body movement is translated into an acceleration of heart rate--the sensitivity and rate of increase is tailored to the needs of each patient following implantation. Heart rate is a major determinant of cardiac output during exercise [11, 21] and single-chamber rate--adaptive pacemakers can improve overall functional capacity compared with conventional single-chamber devices [22]. A recent report suggests an additional role for these pacemakers. Oldroyd et al. compared single-chamber rate-adaptive pacing with conventional dual-chamber pacing in patients with complete heart block and sinus rhythm. In a two-period cross-over study involving patients aged 23-74 years little difference was observed between the two systems in terms of symptoms or exercise performance [23]. In fact only one of the ten study subjects expressed a preference for the conventional dual-chamber pacing mode--he was the only subject with intact ventriculoatrial conduction. The potential advantages of rate-responsive pacing in patients with advanced atrioventricular block include ease of implantation and reduced cost. At the John Radcliffe Hospital a representative rate-response system costs about 1090[pounds] and a dual-chamber system about 1800[pounds] (prices inclusive of electrodes but not VAT). Covert savings may also be anticipated in terms of reduced complication rates. The major disadvantage of single-chamber rate-responsive systems in patients with advanced atrioventricular block is clearly loss of atrioventricular synchrony with the attendant risk of pacemaker syndrome. However, those at risk with intact ventriculoatrial conduction may be identified during pacemaker implantation and offered a conventional dual-chamber system. Clearly a pacemaker policy which includes rate-responsive pacing for selected patients would have significant financial implications and could reduce the financial burden of the working-party guidelines. Additional prospective studies are required before any recommendations can be made on the value of rate-adaptive pacing in patients with complete heart block. Elderly patients in particular may be less tolerant of the loss of atrial synchrony and future studies should specifically include patients over 75 years.

In summary, technological developments have increased both the complexity of pacemakers and their overall cost. The guidelines on pacemaker implantation from the BPEG are a council of perfection; expressing `Ideal' and `alternative' implantation guidelines without directly assessing the financial implications. In these days of budgetary constraints, physicians may find themselves torn between what is considered best for the individual patient and the pacing budget. The guidelines have none the less served to stimulate debate and have prompted others to examine critically their pacing practice. Reported estimates of the financial impact of BPEG guidelines are likely to be exaggerated serving only to support a restrictive and unnecessarily conservative implantation policy. For example, a policy which involves withholding physiological pacing from patients purely on the grounds of age is quite unnacceptable. Published guidelines on implantation policy do serve as a useful starting point but they are no substitute for careful clinical evaluation of each patient and implantation of a pacemaker tailored to their individual needs.


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Author:Hargreaves, M.R.; Ormerod, O.
Publication:Age and Ageing
Date:Nov 1, 1994
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