Comparison of resting hemodynamic indices and exercise performance during atrial synchronized and asynchronous ventricular pacing.

Resting hemodynamic indices and exercise tolerance were measured during atrial synchronized (VAT) and asynchronous ventricular pacing (VOO) in 35 patients with implanted pacemakers which could be externally programmed to function in either pacing mode. Cardiac output and mean systemic arterial pressure were significantly greater during VAT pacing (VAT: 4.5 +/- 1.2 1/min, 115 +/- 28 mmHg; VOO: 3.7 +/- 0.8 1/min 105 +/- 25 mmHg respectively), although there was no difference in pulmonary artery end-diastolic pressure. Maximal exercise performance was assessed using the Bruce protocol in both pacing modes. Neither the patient nor the supervising physician was aware of the preselected pacing mode; a second physician monitored the electrocardiogram and blood pressure but influenced the point of exercise termination only if a potentially dangerous arrhythmia or hypotension occurred. Blood pressure responses were superior and atrial rates lower during VAT pacing. In all but five patients, exercise tolerance was improved by VAT pacing. This amounted to 33 percent or more in 23/35 patients. This improvement was shown to be maintained in the 20 patients who had repeat exercise tests several weeks later. Ventricular arrhythmias, hypotension, and lightheadedness frequently complicated exercise during asynchronous pacing but occurred rarely with atrial synchronized pacing. Resting hemodynamic indices did not predict the extent of improvement gained by physiological pacing.