Dryden Morse

Chronotropic Response of an Activity Detecting Pacemaker Compared with the Normal Sinus Node

We compared the rate responsiveness of an activity‐detecting muitiprogrammable, single chamber pacemaker (Medtronic Acfivitrax) to rate responsiveness of the normal sinus node. This pacemaker changes its basic pacing rate in response to physical activity. The rate responsiveness is programmable by selecting one of three activity thresholds, and one of 10 rate response settings. The study included a group of six normal volunteers and 12 patients implanted with Activitrax to examine the similarity of the pacemaker rate to normal sinus rhythm during acceleration and deceleration. The pacemaker was set to Activity mode, at a basic rate of 60 bpm. In voiunteers, the device was externally secured on the chest wall and tested at two programmed settings. When programmed at a high threshold of activity and high rate response in voiunteers, there was no significant difference in maximum normal sinus rates and pacemaker rates during arm waving, jumping in place, and walking during stress testing. At a medium activity threshold, the only significant difference occurred during submaximal stess testing, when the maximum sinus rate achieved was 141 ± 19 bpm and the maximum pacing rate was 105 ± 8 bpm (p < .02). The pacemaker behaved in a similar manner in patients, successfully simulating the typical fast acceleration and slow deceleration of a normal sinus node in exercise testing. There was no difference in pacer response when implanted in abdominal or in/raclavicular locations. The implanted units have functioned normally over a follow‐up period of nine to 22 months. Activitrax can be programmed to achieve physiologic pacing rates in response to normal daiiy activities with appropriate programming.

Transvenous Pacemaker Insertion with a Zero Dislodgement Rate

A non‐retractable transvenous screw‐in lead which gives both stability of placement and low acute and chronic stimulation thresholds was used in 64 patients during the period April, 1979 to June, 1981. The average threshold at implant was 0.7 volts; the current threshold average was .86 milliamps with the pulse width at the standard setting for the pacemaker employed. Chronic thresholds were usually below the lower programmable limit of the pacer as tested at 3 months. In one patient, the fact that the screw was fixed in the exposed position caused trouble. The lead became knotted in the superior vena cava and was removed by thoracotomy. Although this experience with the Osypka lead was not entirely satisfactory, newer developments with retractable leads may make the principle more acceptable.

Longevity Comparisons Among Lithium Anode Power Cells for Cardiac Pacemakers

Of over 10,000 lithium‐powered pacemakers followed by a commercial franstelephone monitoring service, 148 have been explanted due to rate decline. A breakdown according to the power cell manufacturers shows that the longevity is not uniform, indicating that significant differences exist among the power cell designs even though all have lithium anodes. One tenth of all lithium‐powered pacemakers in the study were explanted for rate declines within 4 years.

Charge Levels in Programmable Pacemakers

The method of calculation of charge in one series of programmable pacemakers is described. Accurate charge tables are constructed and examples of their use are given. With the tables the margin between the threshold and the pacemaker setting can be more precisely determined and consequently, at least in some cases, it can be reduced for greater pacemaker longevity.

Massive Mitral Regurgitation from Chordal Rupture and Coronary Artery Disease

The precise mechanism that causes spontaneous rupture of chordae tendineae remains unknown. That it may occur in patients with no disease other than underlying or associated coronary artery occlusion has not been previously reported. Six patients with chordal rupture were found among 600 patients who underwent operation for mitral regurgitation in a 6-year period. All 6 patients without exception underwent simultaneous mitral valve replacement and coronary revascularization. The salient clinical features of these patients are summarized, and 1 case is reported in detail.

Esophageal P‐Synchronous Pacing

An esophageal electrode can be employed to provide atrial sensing which then can be used to change from temporary right ventriculor (VVI) pacing to P‐synchronous (VAT) pacing. Two cases of postoperative aortic valve replacement, each with new complete heart block (CHB) and dopamine dependency, are presented. In both cases, establishment of P‐synchronous pacing resulted in improved hemodynamic status characterized by successful weaning from dopamine and maintenance of adequafe cardiac output (CO).

Aortic valve disruption after percutaneous aortic balloon valvoplasty

Severe disruption of the aortic valve cusps in patients with aortic valve stenosis can occur during percutaneous aortic balloon valvoplasty. We report such a case treated successfully by aortic valve replacement.

Uncontrolled tachycardia in atrial fibrillation. Management by surgical ligature of A-V bundle and pacemaker.

Abstract An unusual patient with atrial fibrillation is presented whose rapid ventricular rate could not be controlled by conventional medical measures. A search for underlying heart disease and thyrotoxicosis was unrewarding. The tachyarrhythmia did not respond to digitalis, propranolol, reserpine, atrial pacing, or cardioversion. The resultant congestive failure was successfully managed by ligating the atrioventricular conduction pathway and instituting artificial pacing.