Biomedical subjects
Publications and source records attributed to J M Keefe.
We report an unusual pattern of pacemaker function related to the "autocapture" feature of a recently released pacemaker model. The electrocardiogram reveals pacing alternans. This report discusses the differential diagnosis and the correct explanation.
This report describes a case in which an implanted pacemaker programmed to perform noninvasive electrophysiology testing resulted in an unusual form of pacemaker mediated tachycardia. The method of chest wall stimulation was used by programming a unipolar, triggered pacing mode with a short refractory period. In the AAT mode, far-field R wave sensing occurred beyond the physiological atrial refractory period. The triggered atrial response resulted in a single chamber, pacemaker mediated tachycardia.
A graduated sensor indicated response to increased motion levels during equitation was observed in a patient in whom a motion-detecting pacemaker was implanted. Programmable parameters affecting sensor function were preset according to the sensor response observed during the patient's own slow and fast walk. These parameters were generally appropriate for the variety of gaits the horse used while the patient was on horseback.
A unique mechanism of "cross-talk" has recently been described in the Gemini 415A DDD pacemaker in which cross-inhibition of the ventricular output stimulus may occur in the early Gemini 415A models which were manufactured with dual anodal rings interconnected by a wire. The Gemini 415A units with dual anodal rings were implanted under investigational protocol in 53 patients from September 1982 to August 1984. To date, cross-talk has been discovered in six patients during clinical follow-up, manifesting as inappropriate ventricular inhibition. Syncope was documented in one patient. Non-Cordis atrial and ventricular leads were present in all six patients and five patients had at least one chronic lead. Cross-talk was neither evident nor provokable in Gemini 415A units which had compatible Cordis lead systems. Reduction of the atrial output and/or the ventricular sensitivity prevented cross-inhibition in three patients. Cross-talk persisted in three patients despite programming to the lowest atrial output and/or ventricular sensitivity parameters. Cross-talk, spontaneous or provoked, has not occurred in 36 patients having currently designed 415A pulse generators manufactured with a single anodal ring in the ventricular connector channel. We conclude that: this unique form of cross-talk is "design-dependent" and occurs only in Gemini 415As with dual interconnected anodal rings and cannot occur in 415As manufactured with a single anodal ring; this form of cross-talk has occurred only in 415As with non-Cordis leads and appears to be a time-dependent development; reduction of the atrial output or use of pacing modes without atrial pacing or ventricular sensing can prevent cross-talk.(ABSTRACT TRUNCATED AT 250 WORDS)
Omni-Orthocor 234A and 239A are implantable pacers capable of synchronization with an external overdriver. Synchronous or asynchronous burst pacing, synchronized extrastimuli, or a combination of both can be obtained. Upon recognition of a tachycardia, the patient or physician can initiate pace-termination. Omni-Orthocor was implanted in 69 patients (53 for ventricular tachycardia, 11 for supraventricular tachycardia, 2 each with AV nodal reentry and WPW, and 1 patient with concealed accessory pathway). Thirty-five patients performed out of hospital termination. More resistant tachycardias were terminated in the hospital with 76.3% success in VT and only 50% success for SVT. Burst pacing was used in 75% of patients. Noninvasive electrophysiologic study was performed on all patients, and was the sole use of Omni-Orthocor in 20 patients. The device was not implicated in the six sudden death patients in this series.