Thin sections of canine right and left ventricular endocardium and myocardium were studied in a tissue bath to compare conduction properties of intraventricular specialized conducting tissue [Purkinje fibers (PF)], the superficial layers of subendocardial ventricular muscle (SVM), and the deeper ventricular muscle (DVM) below this level. The study was carried out because of observations that some areas of the endocardium, which are devoid of either specialized conducting tissue or of PF-VM junctions between specialized conducting tissue and ventricular muscle, conduct relatively rapidly, favoring specific orientations of propagation. Preparations containing PF, SVM, and DVM were studied electrophysiologically and histologically. A technique of stripping limited areas of endocardium was used to expose DVM in order to determine its intrinsic calculated conduction velocity. In 12 preparations, the average calculated conduction velocity in PF was 1.62 m/sec, and the average in DVM was 0.26 m/sec. The SVM conduction velocity was intermediate between the two, averaging 0.98 m/sec when propagation was parallel to SVM fiber orientation. Conduction velocity transverse to SVM fiber orientation was not significantly different from DVM conduction velocity. Histologically, the most superficial layers of VM were oriented uniformly in the direction of rapid subendocardial conduction, in contrast to DVM fibers in which orientation varied. It is concluded that the geometric arrangement of SVM fibers may provide a means for rapid subendocardial conduction and impulse distribution at a conduction velocity intermediate between PF and DVM in areas devoid of specialized conducting tissue.

SUMMARY In eight patients with chronic ventricular tachycardia and left ventricular aneurysms, we detected delayed ECG wave forms after the QRS complex from the body surface using a high-resolution ECG recorder, amplification and signal averaging. Delayed wave-form activity (D wave) extended a mean of 70 msec beyond the termination of the QRS complex. This delayed activity frequently extended to the limit of the recording window, and may thus continue throughout much of diastole. Antiarrhythmic agents never abolished the delayed activity; however, it was abolished by aneurysmectomy in four patients. Ventricular tachycardia did not recur after surgery in the four patients during a mean follow-up of 1 year. The D wave was not found in eight control patients who had chronic recurrent ventricular tachycardia nor in 11 of 12 who had aneurysms alone. The surface D wave can be readily and reproducibly detected by high-resolution electrocardiography and appears to be specific for patients with left ventricular aneurysms who also have chronic recurrent ventricular tachycardia. This delayed wave-form activity has been noted during catheter and surgical endocardial and epicardial mapping. It may represent persistence of the cardiac impulse in islands of myocardium and may be a manifestation of the delayed and fractionated activity, noted by previous investigators.

SUMMARYIn the course of the evaluation of five patients with left atrial myxoma, it was noted that the movement of the myxoma was related to specific changes in left atrial hemodynamics.

Using intracardiac recording techniques, His bundle (H) and right ventricular apical (RVA) electrograms were recorded in 16 patients with a postoperative electrocardiographic pattern of right bundle branch block (RBBB). Their ages ranged from 5 to 12 years (mean 6.9 years) at surgery and the follow-up period was 1 to 7 years (mean 2.7 years). All were asymptomatic and in sinus rhythm at the time of study. The P-A interval was normal in all and the A-H, H-V, and V-RVA intervals were prolonged in one, one, and six patients, respectively. The V-RNA interval was normal (less than or equal to 30 msec) in ten out of the 11 patients (91%) without associated left anterior hemiblock (LAH), indicating a physiologically intact main right bundle branch, and was abnormally lengthened (45-62 msec) in all five patients (100%) with associated LAH. These findings suggest that there are two subgroups of patients with surgicall-induced RBBB pattern and the measurement of the V-RVA interval in conjunction with the H-V interval may be of ultimate importance in understanding the long-term prognostic implication of surgically-induced RBBB pattern with or without LAH.

Two exercise tests were performed with an intervening rest period of 45 minutes in a group of 13 subjects with previously identified exercise-induced ventricular arrhythmias and no resting arrhythmias. Both normal subjects and patients with heart disease were included in the group. The level of stresss was equal in both tests as judged by similar rate-pressure products at peak exercise. There was a significant decrease (P less than 0.05) in the number of VPCs induced by exercise during and after the second test. When the number of VPCs on test I and test II in the same patients were compared, a regression line fitted the data well (r = 0.92). Analysis of the recovery periods revealed significant (P less than 0.01) decreases in systolic blood pressure at one and three minutes post exercise, comparing the second to the first test. The underlying mechanism may be decreased myocardial oxygen demand during the second test as the lowered rate-pressure products during recovery (P less than 0.01) reflect. The results of this study indicate that tests of effectiveness of an antiarrhythmic drug should not be based solely on a decrease in the amount of severity of ventricular irritability between two successive exercise tests, one immediately before and the other following administration of the drug.