Left ventricular function during physiological cardiac pacing: relation to rate, pacing mode, and underlying myocardial disease.

The hemodynamic effects of cardiac pacing at different rates and in different modes were studied in 21 patients who were candidates for permanent pacemaker implantation. Nine of these had primary conduction disturbances (PCD), ten had ischemic heart disease (IHD), seven with additional cardiac failure (CHF), and two had hypertrophic cardiomyopathy (HCM). In patients with PCD, atrial (AOO) and AV sequential (DVI) pacing did not change systolic blood pressure and pulse pressure but ventricular (VVI) pacing caused a progressive fall in these measurements, especially as heart rate increased. Ventricular volume and stroke volume (counts) derived from radionuclide ventriculography (RVG) decreased progressively with higher pacing rates, especially during VVI pacing. Cardiac output was maintained during VVI pacing by the increase in heart rate; during AOO and DVI pacing, cardiac output increased. Similar but more marked differences were observed in patients with IHD and CHF and the changes were even greater in the patients with HCM. Left ventricular (LV) ejection fraction changed little with increasing heart rate in PCD but decreased progressively with the onset of ischemia in IHD and CHF. There was no difference in ejection fraction in the different pacing modes. Graphs related to LV contractility (end-systolic pressure-volume relations) showed that AOO pacing produced the highest and VVI pacing produced the lowest curves of myocardial contractility in all patient groups, except that at higher rates the AOO curve shifted down again in patients with IHD and CHF, presumably with the onset of myocardial ischemia. This study showed that physiological pacing produced the best hemodynamic results in all patient groups. Higher pacing rates should be avoided in patients with ischemic heart disease while VVI pacing should not be used in patients with HCM. Blood pressure and RVG studies during temporary pacing are useful in selecting the optimal pacing system in an individual patient when the clinical choice is not clear.