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Abstract & Commentary
Synopsis: The basic conclusion is that we should give the patient just what he or she needs and the devices we implant should be designed to fit the patient.
Source: Link MS, et.al. J Am Coll Cardiol. 2004;43:2066-2071.
The Mode Selection Trial (MOST) was a randomized, clinical trial comparing atrially based (usually DDD or DDDR) pacing to VVIR pacing in patients with sinus node dysfunction. This report details the incidence and significance of pacemaker syndrome associated with VVIR pacing in this study.
Patients were eligible for inclusion in MOST if they had a clinical diagnosis of sick sinus syndrome and could receive a dual chamber pacemaker utilizing a transvenous approach. In the study, all patients received a dual chamber pacemaker. Patients were then randomized by programming to either rate modulated ventricular (VVIR) or dual chamber (DDDR) pacing. Baseline data included assessment of retrograde atrial activation and blood pressure responses during ventricular pacing. Quality-of-life measures including the SF-36, the self-reported Quality of Life, a disease specific activity scale, and a functional utility scale were also collected. Initial programming was recommended to be a lower rate of 60 bpm, with rate modulation adjusted to a heart rate of 90 bpm to 110 bpm after a one minute brisk walk. Follow-up was performed at regular intervals. The primary end point in MOST was the first occurrence of stroke or death, but the occurrence of pacemaker syndrome was an important, prespecified secondary end point. Pacemaker syndrome was defined by new or worsened dyspnea, orthopnea, elevated JVP, rales, or edema with VA conduction during ventricular pacing or by symptoms of dizziness, weakness, presyncope, and a 20 mmHg reduction of systolic blood pressure when the patient had VVIR pacing compared with atrial pacing or sinus rhythm. If pacemaker syndrome was diagnosed, programming steps to either lower the ventricular rate or to decrease the sensor driven rate were made. However, if symptoms did not resolve, patients could be crossed over from VVIR pacing to DDDR pacing.
In MOST, 996 patients were randomized to VVIR pacing. The median age was 74 years, and 48% were female. New York Heart Association functional class III or IV heart failure was present in 15%, AV conduction disease, including complete heart block, was present in 26%. Among these patients, 182 (18.3%) met criteria for pacemaker syndrome during the course of the study. By life table analysis, the incidence of pacemaker syndrome was 13.8% after 6 months, 16% at 1 year, 17.7% at 2 years, 19% at 3 years, and 19.7% at 4 years. Among the baseline factors which were analyzed as a predictor of the development of pacemaker syndrome, only a reduced baseline heart rate and a higher programmed ventricular rate were significantly associated with development of pacemaker syndrome. In multivariate analysis, only a higher percentage of beats paced was an independent predictor (P = 0.0001; HR, 1.22 for each 10% increase). The development of pacemaker syndrome was associated with significant decreases in quality of life, as measured by multiple instruments. After cross-over to an atrially-based pacing mode, these parameters improved. The most striking improvements were in measures of energy and physical function.
Link and colleagues conclude that pacemaker syndrome is a common complication of VVIR pacing in patients with sinus node dysfunction. Since prediction of this syndrome is difficult, they argue that all patients with sinus node dysfunction should receive atrial based pacing.
Comment by John P. DiMarco, MD, PhD
There have been a number of trials comparing various modes of pacing in patients with AV block and sinus node dysfunction. After several years of follow-up, these studies have not shown dramatic changes in mortality or stroke incidence, but they have demonstrated a decreased incidence of atrial fibrillation. The development of pacemaker syndrome is another reason why atrially based systems seem to be preferable, but as admitted by Link et al, the data in the literature are inconsistent. In the MOST trial, all patients received a dual chamber pacemaker, and the pacing mode was known to both physicians and patients. Therefore, in patients who knew they were randomized to VVIR pacing and had nonspecific complaints, it was relatively easy for Link et al to try an atrially based pacing mode since a surgical procedure was not required. Although criteria for the diagnosis of pacemaker syndrome had been specified, they may also be seen with other conditions. In MOST, almost 20% of the patients developed what Link et al considered to be a pacemaker syndrome. In contrast, other studies, in which surgical procedures would have been required to change pacing mode, have reported an incidence of pacemaker syndrome of only 2% to 3%. The real incidence probably lies somewhere between these extremes. It is also important to note that many patients with sinus node dysfunction can be managed with just atrial pacing systems. Atrial pacing has the advantage that it requires only a single lead system and avoids the complication of ventricular dyssynchrony that may be induced by right ventricular apical pacing.
There are new functions that are being incorporated into the next generation of pacing that address at least this last issue. Pacemakers can now search the AV interval and try to attempt to minimize the proportion of beats that are ventricularly paced. One system, currently available only in Europe, essentially has separate sensing systems to provide atrial pacing most of the time and ventricular pacing only if heart block develops. These innovations lower the risk that heart block will develop in a patient programmed for just atrial pacing. In conclusion, there is now consistency among all studies that atrial pacing, when possible, is preferable. In the absence of AV block, avoidance of ventricular pacing is also preferable. The basic conclusion is that we should give the patient just what he or she needs, and the devices we implant should be designed to fit the patient. Ventricular pacing in patients with sinus node dysfunction then becomes the choice only when other factors preclude effective atrial pacing.
Dr. DiMarco, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville, is on the Editorial Board for Clinical Cardiology Alert.