Mobile instrumentation and a clinically applicable method have been developed for external His bundle recording. High gain signal amplification (10)(5) filtering (30--300 HZ) and averaging (128 or 256 consecutive cycles) are used. Acquisition of signals arising in the P-R interval is triggered by the patient's QRS signal at the end of that interval. The precordial bipolar electrodiogram is digitized at 5k HZ with 8 bit resolution and transferred to a 1,024 word, 18 bit signal averager. The averaged signal is then displayed on an oscilloscope and photographed. Good correlations were obtained between direct intracardiac and precordial recordings in experimental animals and in humans. Noise level after averaging was below 0.3 microV, and there was good elimination of asynchronous atrial and ectopic ventricular activity. With averaging of 128 or 256 consecutive cycles, the signal attenuation after propagation to the chest wall was in the range 1:2000 to 1:4000 in comparison with the directly recorded His bundle activity deflections. The noninvasive method may be of value in follow-up of acute and chronic disturbances of atrioventricular conduction, as well as in studies of effects of pharmacologic interventions.

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Short-term coronary ischemia was produced in dogs anesthetized with pentothal by ligating the left anterior descending coronary artery. The resulting changes in representative hemodynamic parameters and the patterns of segmental contraction within and outside the ischemic area were recorded. Two types of reaction to coronary ligation were obtained: in some animals the contractility of the ischemic area rapidly decreased, leading to ballooning of the cardiac wall, inversion of the segmental contraction trace, marked reduction in stroke volume, pronounced increase in ventricular end-diastolic volume, and significant reduction in rate of intra-ventricular pressure rise (dP/dt). In other animals there were no signs of functional ventricular aneurysm, the changes in ventricular end-diastolic volume were less marked, and dP/dt was not altered to a significant extent. These observations suggest that in these cases characterized by the development of a functional aneurysm, the decrease in stroke volume does not result solely from dilation of the entire left ventricle, but also from the increased requirement for systolic fiber shortening in the viable myocardium, which must compensate for the extra stretch in the aneurysmal portion of the ventricular wall. It is suggested that diminution of stroke volume is due not only to the increase in wall stress in the whole left ventricle; it owes also to the expending of contractile elements in the viable portion of the muscle to compensate for additional elasticity in the functional left ventricular aneurysm.

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A mobile instrumentation and noninvasive method developed recently for external His bundle recording and employing the signal averaging technique was applied for intra-atrial recording of the pre-P (sino-atrial node region) activity. Recordings were obtained in ten anesthetized dogs and five patients at the time of right heart catheterization. A bipolar intra-atrial lead was used for triggering of the averaging process and a unipolar intra-atrial lead was used for signal recording. Direct bipolar epicardial recordings were obtained for comparison from the sino-atrial (S-A) node area in experimental animals. In animals studies, the averaged intra-atrial recording showed 30 muV amplitude deflections beginning 40-45 ms prior to the onset of P wave and were preceded by a slow rise and lower frequency and amplitude deflections arising 60-70 ms earlier. There was good correlation between the pre-P activity recorded intra-atrially and from the epicardium. Deflections of similar configuration but smaller amplitude (1 muV) were recorded in human studies. They preceded the onset of large atrial activity deflections (P wave) in the reference electrocardiogram by 40-80 ms. The exact source of these pre-P activity potentials has not been definitely established, but they appear to originate from the S-A node region, based on their similarity to the direct epicardial recordings and time relationship to the preceding T and following P wave.