Atrial Electrodes Research Articles

Permanent pervenous atrial pacing

A “J” shaped electrode catheter designed to fit in the right atrial appendage has been studied in the dog and in man. The atrial electrode catheter is less stable than its ventricular counterpart and fixation may be expected only occasionally in man. Displaced electrode catheters are however easily replaced. In five patients atrial pacing could not be established. Stable atrial pacing was achieved in 14 of the 16 patients in whom it was established. P wave potentials are much lower in man than in the dog and are often marginal for the sensitivity of the presently available pulse generator. Atrial stimulating thresholds are higher than ventricular thresholds in the dog and in man, possibly due to less intimate contact with the endocardium than occurs in the ventricle. Preoperative study of A-V conduction is essential before initiating permanent atrial pacing to screen out the patients likely to develop A-V block at a later date. Postoperative study of A-V conduction is equally important to anticipate this complication in patients in whom atrial pacing has already been established. The P.S. (P wave stimulated) standby principle simplifies this since external overdrive can be used to check if the capacity of the A-V node for conduction is diminishing, as shown by a drop in the rate at which A-V block begins. This feature is not available with either P.I. (P wave inhibited) demand, or fixed rate atrial pacing.

Studies on left atrial automaticity in dogs.

The site of origin and the sequence of atrial activation were studied in 21 open-chested dogs anesthetized with sodium pentobarbital. Bipolar plunge electrodes were used to record atrial electrograms simultaneously with surface lead II and His bundle electrogram. In sinus rhythm the sinus node was activated first, followed sequentially by Bachmann's bundle, right atrial appendix, left atrial appendix, posterior left atrium, and the proximal portion of the coronary sinus. In 15 dogs left atrial beats and rhythms of various rate were recorded, including instances of left atrial exit block and of rapid left atrial rhythms. In such beats one of the left atrial electrodes was activated first and was followed by Bachmann's bundle, sinus node, proximal portion of the coronary sinus, and by right atrial appendix. Left atrial beats were observed occurring (1) spontaneously; (2) as a result of vagal stimulation; (3) after destruction of the sinus node; (4) during ventricular pacing. Left atrial pacing through the electrode recording initial activity reproduced the sequence and configuration of atrial electrogram similar to that seen in the ectopic left atrial beats. These results demonstrate that in dogs ectopic activity frequently originates in the left atrium.

Atrial pacing after mitral valve surgery.

WITH progressive sophistication of the operative treatment of heart disease and expansion of operability limits to include more precariously ill patients, the problems of postoperative myocardial depression with increased rhythm instability have assumed increased importance. Surgeons at the University of Oregon and University of Illinois hospitals have been investigating the use of atrial pacing as one means of meeting these problems. Cardiologists and physiologists have employed atrial electrodes as experimental tools for the study of cardiac function, 1 and subsequently in the clinical setting for the evaluation of complex arrhythmias and intracardiac shunts 2,3 and for treating occasional cases of ventricular irritability. 4,5 However, it was not until recently that the value of atrial pacing as a surgical adjuvant for maintaining optimum postoperative cardiac output and synchronous rhythm stability was first reported. 6,7 Other authors have since described similar results with this technique, 8,9 but heretofore no reports have attempted

Hemodynamic Results of Right Atrial Pacing in Cardiac Subjects

The effect of increasing heart rate above control sinus rate was investigated in 136 patients with pulmonary emphysema or rheumatic or congenital heart disease. Bipolar right atrial electrode catheter pacing was utilized to increase the atrial rate. At all atrial pacing rates, significant cardiac output increments are noted compared to the outputs during the control sinus rates. The cardiac indices are generally similar at the various atrial pacing rates.

Effect of Changing Heart Rate on Cardiovascular Function in the Conscious Dog

The effect of heart rate on the cardiovascular system of the conscious dog was studied by pacing the heart with an implanted right atrial electrode. Left ventricular outflow was measured by an electromagnetic flowmeter with a chronically implanted transducer on the ascending aorta. As heart rate increased, stroke volume fell, and this was linearly related to heart rate over the entire range studied. Peak flow rate and maximum acceleration decreased as heart rate increased, but the change was small compared with that in stroke volume. The decrease in stroke volume resulted principally from a loss of volume ejected in late systole. An increase in heart rate sometimes resulted in a rise of cardiac output, and when this occurred mean arterial pressure rose; when cardiac output did not increase, mean arterial pressure also remained unchanged. The data suggest that there is a pressure for the systemic circulation analogous to the "critical closing pressure" of peripheral vascular beds. It was shown that in these circumstances changes in calculated systemic resistance may not reflect any real alterations in the peripheral vascular beds.

Production and abolition of alternation in mechanical action of the ventricle.

Persisting alternation in mechanical response of the ventricle, pulsus alternans, develops when the heart is driven above certain rates. This critical rate varies, but tends to occur between rates of 200 and 300 beats/min. The ventricle can be driven slightly faster (10–20 beats/min) by direct than by indirect drive, through atrial electrodes, without showing pulsus alternans. There is a rate "threshold" for persisting alternation which represents the rate limits of compensation. Alternation appears at lower rates but the contractile process can gradually accelerate and alternation disappears even in denervated hearts and after adrenalectomy. Slower progressive accelerations delay onset of pulsus alternans and compensation occurs more quickly than when stepwise rate changes are made. Fast drives above the threshold for pulsus alternans can produce some additional acceleration of the contraction-relaxation process: if the rate is reduced to a level which previously produced a persisting alternation, pulsus alternans does not occur for a number of seconds. The resemblances of these phenomena to "treppe" and "postextrasystolic potentiation" and implications relative to catecholamine release and action are discussed.