Relation of atrio-ventricular systolic interval to left ventricular function

Hypotension with ventricular pacing: an atria vasodepressor reflex in human beings

Hypotension with ventricular pacing has generally been attributed to loss of atrial transport, but it has been suggested that atrial vasodepressor reflexes may play a role. To study this, constant rate atrial and ventricular pacing was performed in 20 supine patients 24 to 36 hours after surgical coronary artery bypass or aortic valve replacement. The pulmonary capillary wedge tracing was examined for the presence or absence of cannon A waves during ventricular pacing in each patient. Thirteen patients had cannon A waves (group I) and seven did not (group II). Ten of the 13 patients with cannon A waves had ventriculoatrial conduction compared with only 2 of 7 patients without cannon A waves. There was a nonsignificant trend toward an association between cannon A waves and ventriculoatrial conduction (p = 0.1). Stroke volume index decreased in both groups when patients were changed from atrial to ventricular pacing. In the patients with cannon A waves, stroke volume index decreased from 31.2 to 26.3 cc/min per m2 (p less than 0.001) and from 31.2 to 25.0 cc/min per m2 (p less than 0.001) in those without cannon A waves (group I versus group II, p = NS). However, mean systemic blood pressure decreased only in patients with cannon A waves (99.4 to 85.9 mm Hg [p less than 0.001] versus 101.8 to 100.9 mm Hg [p = NS]) in those without cannon A waves (group I versus group II, p less than 0.001). Hypotension in patients with cannon A waves was caused by inhibition of the normal reflex increase in systemic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of left ventricular performance by left bundle branch block simulated with atrioventricular sequential pacing

The effects of atrioventricular (AV) sequential pacing-induced left bundle branch block (LBBB) on left ventricular (LV) performance were evaluated during cardiac catheterization in 9 randomly selected patients being investigated for chest pain. All patients were in normal sinus rhythm with a normal P-R interval and QRS duration. LV performance was assessed by both hemodynamic and angiographic measurements. The maximal rate of LV pressure increase (dP/dt), rate of maximal LV pressure decrease (-dP/dt), LV end-diastolic pressure (LVEDP), end-diastolic volume (LVEDV), end-systolic volume (LVESV), stroke volume and percent ejection (EF) were measured during right atrial and AV sequential pacing at a constant pacing rate. The average pacing rate was 97 +/- 3 beats/min (mean +/- standard error of the mean). In each patient, both dP/dt and -dP/dt decreased significantly (p less than 0.001) during AV sequential pacing compared with atrial pacing at the same rate, from 1,541 +/- 68 to 1,319 +/- 56 mm Hg/s for dP/dt and from 1,506 +/- 86 to 1,276 +/- 92 for -dP/dt. LVEDP did not change significantly when atrial (17 +/- 3 mm Hg) and AV sequential pacing (16 +/- 2 mm Hg) were compared. Mean LVEDV did not change during atrial (135 +/- 13 ml) or AV sequential pacing (137 +/- 14 ml). In contrast, the LVESV during AV sequential pacing was higher by 15 ml (23%) (from 48 +/- 10 to 63 +/- 12 ml) (p less than 0.001); as a result, the stroke volume was lower by 13 ml (15%) and the EF decreased by 10%, from 66 to 56% (-15%).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of ventricular pacing on left ventricular function assessed by radionuclide angiography

Radionuclide angiography was used to evaluate left ventricular contraction on and off ventricular pacing in 35 patients. Twenty patients had permanent rate-adjustable ventricular demand pacemakers whose rate could be programmed to below an underlying sinus rhythm. In these patients there was no difference in left ventricular ejection fraction on and off pacing whether or not heart failure was present (n = 7) or whether or not ventriculoatrial conduction (n = 10) developed during pacing. Eight of the 20 patients also underwent supine bicycle exercise, and rest and exercise ejection fraction values were not significantly different at a similar heart rate and workload when on and off pacing were compared. During pacing, there appeared to be abnormal motion in septal, apical, and inferior walls. In addition, dysynchrony developed, consisting of early right ventricular and anterobasal and posterobasal left ventricular motion with subsequent contraction of the apex. Conversion to atrioventricular pacing produced a clinical improvement in all seven patients with heart failure and reduced ejection fraction and also in one of the remaining 13 patients without heart failure. Fifteen other patients were studied early after cardiac surgery. Temporary ventricular epicardial pacing resulted in a significant increase in right and left atrial pressure and a significant reduction in stroke volume, end-diastolic volume, and end-systolic volume with no significant change in ejection fraction. Conversion from sinus rhythm to ventricular pacing produces a deterioration in cardiac performance and severe regional left ventricular wall motion abnormalities, but no significant change in ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)