Regional myocardial blood flow in patients with sick sinus syndrome randomized to long-term single chamber atrial or dual chamber pacing - Effect of pacing mode and rate

OBJECTIVES This study aimed to evaluate regional myocardial blood flow (MBF ) and global left ventricular ejection fraction (LVEF) during chronic pacin g in patients with sick sinus syndrome (SSS) randomized to either single ch amber atrial (AAI) or dual chamber (DDD) pacing. BACKGROUND Experimental studies indicate that chronic pacing in the right v entricular apex changes regional MBF, thereby compromising left ventricular function. METHODS Thirty patients (age 74 +/- 10 years) were randomized to AAI (n = 1 5) or DDD (n = 15) pacemakers. After 22 +/- 7 months of pacing, MBF was qua ntified with N-13-labeled ammonia positron emission tomography scanning at 60 beats per min and 90 beats per min. Patients in the DDD group furthermor e underwent MBF measurement at temporary AAI pacing, 60 beats per min, Myoc ardial blood flow was assessed in the anterior, lateral, inferior and septa l regions, and the global mean MBF was calculated. Left ventricular ejectio n fraction was determined by echocardiography at pacemaker implantation and at the time of MBF measurements. RESULTS Myocardial blood flow at rates 60 and 90 beats per min did not diff er between the AAI and DDD groups. During temporary AAI pacing in the DDD g roup, MBF was significantly igher than during DDD pacing in both the inferi or (p = 0.001) and septal (p = 0.004) regions and also globally (0.61 +/- 0 .15 vs. 0.53 +/- 0.13 mL.g(-1).min(-1), p = 0.005). In the DDD group, LVEF decreased from pacemaker implantation to time of MBF measurements (0.61 +/- 0.09 vs. 0.56 +/- 0.07, p = 0.013). Left ventricular ejection fraction dur ing temporary AAI pacing at time of MBF measurements was not different from LVEF at pacemaker implantation. CONCLUSIONS In patients with SSS, chronic DDD pacing reduced inferior, sept al and global mean MBF as well as LVEF, as compared with temporary AAI paci ng. The LVEF reversed to baseline level during temporary AAI pacing despite 22 months of permanent ventricular pacing preceding it. Augmenting pace ra te to 90 beats per min increased MF equally in the two treatment groups. (C ) 2000 by the American College of Cardiology.