A new temporary pacing catheter with improved sensing and safety characteristics

A temporary external DDD pacing unit

A device for temporary external DDD pacing was developed using a modified permanent pulse generator, and temporary atrial and ventricular electrode catheters were inserted pervenously. The atrial lead was a J type and the ventricular lead had a remote anode in the superior vena cava. With a special clamp and appropriate connectors the permanent DDD pulse generator provided unipolar external DDD pacing. The device was evaluated in 13 patients to control bradyarrhythmias or for overdrive pacing in an attempt to control tachyarrhythmias. Nine patients were ambulatory; all had continuous electrocardiographic monitoring. The device was used for 1 to 12 days (mean 4.9). Eight patients benefited from temporary DDD pacing and 7 had permanent DDD pacemakers implanted. In 1 patient, atrial fibrillation developed, 2 patients had brief episodes of ventricular lead displacement and another required reprogramming because of loss of ventricular capture. Results suggest that the device is applicable for a clinical trial of DDD pacing before possible permanent implantation when attempting to improve cardiac output or control arrhythmias.

Temporary unipolar pacing using a dual cathode

Using standard biopolar, temporary pacing catheters, thresholds were measured in four configurations: (1) bipolar (distal electrode negative, proximal electrode positive); (2) distal unipolar (distal electrode negative, right arm electrode positive); (3) proximal unipolar (proximal electrode negative, right arm electrode positive); (4) dual-cathode unipolar (distal and proximal electrodes negative, right arm electrode positive). With one exception, the bipolar threshold was the lower of the distal or proximal unipolar thresholds, suggesting that bipolar temporary pacing is reliable because one of the two electrodes is in good contact with the endocardium. In both the distal and proximal unipolar configurations there were numerous instances of high threshold and failure to pace. However, with one exception, in all cases either the distal or proximal unipolar threshold was normal and thus pacing was possible and effective in the dual-cathode configuration. Dual-cathode unipolar pacing combines the excitation and sensing advantages of unipolar pacing with the reliability of bipolar stimulation.

Clinical applications of the threshold tracking pacemaker

The concept of automatic threshold tracking is the most recent adaptation of artificial cardiac pacemakers to physiologic needs. Earlier pacemaker innovations were primarily in the area of timing of impulse delivery, whereas more recent changes have focused on alteration of the amplitude and duration of the pacemaker stimulus. Matching of this stimulus to the cardiac excitation threshold is important because a stimulus greater than necessary is wasteful of battery energy and may produce arrhythmias, whereas a stimulus of less than threshold intensity fails to pace the heart. Because of the wide range of clinically encountered threshold levels it is impossible to design a fixed output pacer that is efficient and safe for all patients at all times. The threshold tracking pacemaker searches for and finds the threshold level, and adjusts its stimulus to just above this level. The device ensures an adequate safety margin of stimulation, but reduces the stimulus level to the lowest safe level possible. It is fully automatic, adjusts immediately to any threshold changes and is not dependent on manual alteration.