Single-chamber versus dual-chamber pacing for high-grade atrioventricular block
In the period under review (June 1989 to June 1997), 2614 patients received permanent pacemakers: 794 (31%) dual chamber, 1820 (69%) single chamber.Of those who received single chamber units, 986 were paced for high grade atrioventricular block (628) or sinus node disease (358), of whom 44 (4.5%) have subsequently undergone upgrading of single chamber ventricular units to dual chamber units. Information regarding indications for upgrade, procedure duration, complications, symptom response, and subsequent clinical course were analysed.
Mean (SD) upgrade procedure duration (82.9 (32.6) minutes) significantly exceeded mean VVI implantation duration (42.9 (13.3) minutes) and mean DDD implantation duration (56.6 (22.7) minutes) (both p Since the introduction of the dual chamber pacemaker,1 “upgrading” of single chamber ventricular pacemakers to dual chamber units has been a possibility in patients with persisting atrial electrical activity.
Current guidelines suggest that patients with intrinsic atrial activity should receive dual chamber implants (or single chamber implants if appropriate),2 3 but in the United Kingdom 40% of patients paced for high grade atrioventricular block during 1995 received fixed rate ventricular pacing systems (National Pacemaker Database, 1996) for reasons that were likely to include age,4 5 cost,6 relative inactivity,4 and intermittency of atrioventricular block.7 Patients receiving such relatively simple systems lack atrioventricular synchrony and a proportion (variously estimated at between 15% and 70%8-11) go on to experience symptoms of the pacemaker syndrome.10 12 These patients, and those whose symptoms persist for other reasons (such as heart failure), may be considered for pacemaker upgrade.
Physiologic pacing may reduce morbidity by decreasing the incidence of atrial fibrillation 10; 11; 12 ; 13, thromboembolic phenomena 6 ; 13and congestive heart failure 12 ; 14and affect the quality of life by improving effort tolerance and general well-being .
However, the effect of pacing mode on long-term survival, especially in the very elderly, is not clear.
The impact of pacing mode in octogenarians and nonagenarians is more difficult to establish because of the high prevalence of coexisting illnesses, the nonspecific nature of symptoms, shorter life expectancy and limited availability of long-term follow-up data.