Clinical Characteristics of Patients Intolerant to VVIR Pacing
abstract & commentary
Synopsis: Intolerance to VVIR pacing is frequent in elderly patients but it is difficult to predict from baseline measurements those who will require DDDR pacing.
Sources: Ellenbogen KA, et al. Am J Cardiol 2000; 86:59-63.
The pacemaker selection in the elderly (pase) trial was a single-blind, randomized comparison of ventricular pacing and dual-chamber pacing in 407 patients older than 65 years of age. Patients in PASE all received a dual-chamber pacemaker for treatment of bradycardia. Patients were required to have a stable atrial rhythm at the time of implantation. After enrollment, patients were randomized to either the DDDR mode or the VVIR mode. During the implant procedure, baseline blood pressure was measured during intrinsic rhythm and after one minute of ventricular pacing at 10 bpm faster than the intrinsic rhythm. The presence or absence of retrograde ventricular retrograde atrial conduction was also determined. Patients were followed at prescribed intervals after enrollment. Their health status was assessed with the 36-item Medical Outcomes Study Short Form general health survey (SF-36).
During the study, 53 of the 203 patients initially randomly assigned to the VVIR pacing mode crossed over to the DDDR mode. Seven of 53 (13%) crossed over before hospital discharge, 16 of 53 crossed over within one month of implant, and another 17 crossed over before six months. Patients were crossed over from VVIR to DDDR pacing because of the presence of one or more symptoms including: fatigue, effort intolerance, dyspnea, and presyncope. Independent predictors of crossover were the use of beta-blockers, the presence of nonischemic cardiomyopathy, and a systolic blood pressure of less than 110 mmHg during ventricular pacing. Data from the SF-36 survey were available in 29 patients who crossed over from VVIR to DDDR pacing. Among these 29, there was an improvement in multiple factors, including physical and social function and physical and emotional roles.
Ellenbogen and associates conclude that intolerance to VVIR pacing is frequent in elderly patients but that it is difficult to predict from baseline measurements those who will require crossover.
Comment by John P. DiMarco, MD, PhD
Intolerance to ventricular pacing was first observed in patients with acute myocardial infarction (MI) who were treated with temporary ventricular pacing. At that time, it was shown that retrograde VA conduction produced cannon A waves with a marked decrease in cardiac output and blood pressure. Similar observations were soon reported in patients with permanent pacemaker systems outside of the setting of acute infarction. Dual-chamber or physiologic pacing was then introduced in hopes that this problem would be eliminated. However, controversy still exists about the magnitude of benefit that should be seen with dual-chamber and physiologic pacing systems.
The PASE trial attempted to address this hypothesis. One important feature of the study design was that all patients had a dual-chamber pacing system implanted. Even though the protocol had some barriers to prevent crossover to a dual-chamber pacing mode from VVIR pacing, a high proportion of patients in this study were crossed over for clinical reasons. Crossover only required reprogamming the device. However, it is important to recognize that crossover has been much less common in studies where a surgical procedure is required to change pacing mode. For example, in a trial of patients with sinus node dysfunction that compared AAI and VVI pacing, only 1.7% of patients were crossed over to a physiologic pacing system over an eight-year period (Lancet 1994;344:1523-1528). Similarly, in the Canadian Trial of Physiologic Pacing, only 4.3% of patients initially assigned to ventricular pacing were crossed over to physiologic pacing over a five-year period (N Engl J Med 2000;342:1385-1391). It therefore seems likely that in studies where crossover involves merely a programming change, investigators and patients are much more likely to attribute symptoms to the mode of pacing. The desire of the physician and patient to try something relatively simple leads to reprogamming and crossover. Total elimination of investigator and patient bias toward crossover would be difficult unless both were kept blinded to the mode of pacing used.
Despite numerous studies, the magnitude of benefit over single-chamber ventricular pacing that can be expected with dual-chamber or physiologic pacing remains uncertain. The simplicity and lower cost of VVIR pacing is balanced by questions that may arise during chronic therapy about possible advantages that might be derived from a physiologic pacing system. At this point, published data don’t allow us to reach firm conclusions.