Effects of Right Ventricular Pacing on Coronary Artery Blood Flow

Implantation of atrio-ventricular dual chamber (DDD/R) pacemakers is performed in the majority of patients with sick sinus syndrome. Right ventricular pacing alters electrical conduction leading to dyssynchrony of myocardial contraction and thus may lead to left ventricular dysfunction and heart failure. Aim: Evaluation of the effects of DDD pacing on coronary artery blood flow. Methods: Twenty six patients with sick sinus syndrome, dual-chamber atrio-ventricular pacemaker and preserved atrio-ventricular conduction were evaluated. All had complete baseline transthoracic Doppler echocardiographic studies. Right atrial pacing was compared to DDD pacing at different pacing rates from 70bpm to 110bpm.  AT each stage and pacing mode, sampling of blood velocity of the left anterior descending coronary artery (LAD) was performed. In addition, ventricular outflow and inflow velocities as well as well as tissue Doppler imaging were performed. Results: During pacing rates 70-90bpm, peak diastolic LAD velocities and time velocity integrals were significantly lower during DDD pacing compared to right atrial pacing, however at pacing rates 100-110bpm these parameters were similar. Coronary artery flow index evaluated as the product of heart rate and LAD diastolic time velocity integral were lower during pacing rates 70-90bpm during DDD pacing compared to right atrial pacing. Myocardial oxygen supply/demand ratio index evaluated as the ratio of LAD diastolic velocity integral/ systolic blood pressure ratio was lower during DDD pacing. Conclusions: Atrioventricular dual chamber pacing is associated with reduction in LAD diastolic blood velocity and integral, lower coronary flow and lower myocardial blood flow/ oxygen demand ratio.