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The atrial fibrillation threshold was measured in 10 anesthetized dogs by delivering a series of impulses directly to the right atrium after infusion of 4.5 ml of 5% glucose per kilogram of body weight, and after 1.5 ml of absolute alcohol per kilogram in 3 ml/kg of 5% glucose. There were no changes in the atrial fibrillation threshold after glucose. The mean AFT before alcohol was 6.8 volts. Immediately after alcohol infusion, the arterial blood alcohol concentration (BAC) was 300.7 mg/100 ml, and the AFT increased to 9.75 volts (P less than 0.01); 20 minutes later the BAC was 181.2 mg/100 and the AFT 8.5 (P less than 0.02). There was no rebound decrease in AFT up to 65 minutes. The findings suggest that in anesthetized normal dogs, alcohol may have a direct mild antiarrhythmic effect on the atria. Atrial fibrillation in alcoholics may be due to alcohol indirectly through electrolyte, autonomic, or histologic changes.

In order to study the effect of age, blood pressure and gender on premature ventricular contractions (PVCs), 24-hour ambulatory electrocardiography was performed on 338 apparently normal subjects (Group I; 209 men, 129 women, age 17 to 69, mean 48.5 +/- 11.7) and on 100 subjects with normal hearts proven by extensive invasive and noninvasive testing (Group II; 51 men, 49 women, age 16 to 68, mean 48.8 +/- 10.2). Apparently normal subjects (Group I) had a higher prevalence of PVCs (61.8% vs. 39.0%, p less than 0.001) and of complexity (16.3% vs. 4.0%, p less than 0.003) than subjects with normal hearts (Group II). The distribution of subjects according to PVC frequency was bimodal in Group I and unimodal in Group II. PVC prevalence increased with age in both the apparently normal group (p less than 0.001), and in the group with normal hearts (p less than 0.025). On the contrary, apparently normal (Group I) men had almost twice the PVC prevalence (74.6% vs. 41.1%, p less than 0.001) and complexity (20.1% vs. 10.1%, p less than 0.25) than apparently normal women, while gender had no effect on PVC prevalence in subjects with normal hearts (Group II). Systolic blood pressure was also associated with PVC prevalence (p less than 0.001) and complexity (p less than 0.02) in apparently normal subjects (Group I) but not in subjects with normal hearts (Group II). These data indicate: that apparently normal subjects have higher prevalence of PVCs and of PVC complexity than subjects with normal hearts, probably because of undetected cardiac disease; that the increase in PVC prevalence with age is not necessarily due to cardiac disease; and that PVC complexity in apparently normal subjects should raise the suspicion of cardiac disease especially in men, in subjects with hypertension and in the older age group.

To further elucidate the value of the R wave criteria during the exercise stress test (EST), we studied the direction and magnitude of the changes of the QRS amplitude (delta R) as well as the extent of ST segment depression in 75 patients with coronary artery disease (CAD) and 26 normal subjects (NLS). Results were analyzed in relation to severity of the disease (number of vessels involved) and left ventricular EF. In NLS, there was an average decrease of the QRS amplitude of --1.9 +/- 0.6 mm (mean +/- SE) compared to an average increase of 0.6 +/- 0.35 mm for CAD patients. Mean delta R for 1VD was --0.28 +/- 0.75 mm; for 2VD, it was 0.27 +/- 0.54 mm, and for 3VD, it was 1.37 +/- 0.55 mm. Mean delta R for NLS was significantly different (Duncan's multiple range test, p less than 0.05) from 2VD and 3VD but not from 1VD. Although there was no statistically significant difference of mean delta R among CAD groups, a significant linear trend was observed (p less than 0.008). Resting EF did not correlate either with extent of ST segment depression or with the direction or magnitude of delta R induced by exercise. We conclude that the direction of changes in delta R during exercise is related to the presence or absence of CAD. The magnitude of delta R appears to correlate with the severity of coronary arterial involvement. We did not detect any relationship between R wave changes and left ventricular function. The use of R wave criteria may slightly improve the sensitivity of EST but detracts from specificity.

beta-Blockers are effective in the symptomatic relief of angina pectoris by decreasing myocardial oxygen demand during effort and emotional stress. Agents with ISA such as pindolol produce effective beta-blockade during effort or emotional stress while conferring significant protection from myocardial depression and bradycardia at rest. In addition, agents with ISA have been shown to depress respiratory function to a lesser extent and to induce fewer peripheral vascular side effects than compounds devoid of this property. These potential effects of ISA may be counterbalanced by the consideration that ISA may be undesirable in angina occurring at rest or at low exercise levels. Additional well-controlled trials in patients with angina and resting bradycardia or impaired left ventricular function are needed to further document the clinical importance of ISA.