J.G. Davies

T-WAVE CHANGES AFTER ARTIFICIAL PACING

Abstract Massive T-wave inversion and ST depression occurred in unpaced electrocardiograms of 31 patients after ventricular pacing, whether endocardial or epicardial, and were related to the power of the artificial electric stimulus and not to the presence of the electrode alone. They continued as long as pacing was continued but were always reversible. They should not be mistaken for evidence of myocardial injury or underlying coronary disease.

LOW INTRACARDIAC POTENTIALS IN MYOCARDIAL INFARCTION AS A CAUSE OF FAILURE OF INHIBITION OF DEMAND PACEMAKERS

Abstract In demand (ventricular inhibited) endocardial pacing for heart block, the signal used to inhibit the pacemaker is the intracardiac QRS potential. When this potential falls below the predetermined minimum that will inhibit the pacemaker, the unit behaves as a fixed-rate apparatus. In a series of forty patients with heart block after myocardial infarction, low intracardiac potentials which failed to inhibit the pacemaker were observed in six (15%). Although an increase in unit sensitivity will achieve inhibition of the pacemaker by the low potential, the risk of inappropriate inhibition of the unit by mains-frequency becomes appreciable. Further work is required on the elucidation of this clinical phenomenon and its management.

EXPERIENCE WITH IMPLANTED PACEMAKERS: TECHNICAL CONSIDERATIONS.

Between April 1960 and September 1964, 79 patients were treated with implanted pacemakers. We record here the technical difficulties encountered and the steps taken to overcome them. In all cases the indication for artificial pacing was failure of medical treatment to prevent Stokes-Adams attacks or to relieve cardiac failure due to a slow pulse. Most, but not all, patients were in complete heart block. Fuller clinical details are being published elsewhere (Harris, Bluestone, Busby, Davies, Leatham, and Siddons, in press). Throughout the period under consideration (up to 30 September 1964) 143 pacemakers were implanted in these 79 patients. The first two were of Swedish make*. but subsequently pacemakers designed by one of us (J.G.D.) have been used exclusively, some of them having been made in the electronics department of St. Georges Hospital and some to our designt. In treating 19 of our early patients a number of prototype units were tried, some from outside with only a receiver unit implanted, and others containing their own battery for power; some could be turned on and off, speeded up, and slowed down from outside. However, as a result of experimental work done in this hospital (Sowton, 1963), an early decision was taken to concentrate on the development of a fixed-rate pacemaker powered by miniature mercury cells within the implanted unit. There was no time for prolonged laboratory or animal trials since patients with complete heart block in whom Stokes-Adams attacks threatened life required pacing without delay. Thus it has proved necessary to modify the apparatus as faults revealed themselves during clinical use (see Table 1). The earliest patients were treated with a pacemaker implanted in the rectus sheath with wires leading to the surface of the heart (epicardial system) (Fig. 1). A high proportion developed sinuses and many of the pacemakers had to be taken out. Before this complication reached serious propor-

The detection of impending failure in implanted pacemakers

As implantable pacemakers last a variable time, it is desirable to be able to foretell when each individual pacemaker is nearing the end of its life. A test which detects a number of different impending electronic failures including battery depletion is described. The test requires only standard laboratory equipment and has been used for four years as a three-monthly procedure in an out-patient clinic. In 17 of 19 consecutive patients the test has enabled a change of pacemaker to be carried out electively. rather than after an arbitrary period or as an emergency when pacing has failed.

MANAGEMENT OF HEART-BLOCK

Syncope or dizzy spells with near syncope are common in the elderly. Whether or not there is gross bradycardia, such symptoms require, among other investigations, an ECG. If the ECG taken between attacks shows complete block, the likelihood is that the syncope (Stokes-Adams attack) is due to a temporary cessation of the cardiac rhythm. Asystole, ventricular tachycardia, or ventricular fibrillation may each occur. Such attacks can be reliably prevented only by artificial pacing. Although long-acting isoprenaline has often been used, there is little or no evidence that any drug therapy is effective. If the ECG taken between syncopal attacks shows lesser degrees of block or bundle branch block, it is highly probable that the syncope is cardiogenic, although many of these rhythms without syncope are relatively benign. Syncope from cessation of the heartbeat is exceptional when the ECG between attacks shows no conduction defect. Syncopal attacks associated with block are usually both infrequent and unpredictable; thus, continuous monitoring to determine the rhythm during an attack is usually impractical.