Edgar Sowton

HAEMODYNAMIC STUDIES IN PATIENTS WITH ARTIFICIAL PACEMAKERS.

The treatment of complete heart block bymeans of an artificial pacemaker is now well established, but there is still considerable uncertainty as to the best heart rate and the relative merits of fixed or variable rate units. The present study is based on 35 patients and the results are supported by clinical experience of a further 41 who have all been treated by artificial pacing for up to four years.

ARTIFICIAL PACEMAKING AND SINUS RHYTHM

The patients reported form part of a larger series of 60 patients with Stokes-Adams disease treated with artificial pacemakers, which is being reported in full elsewhere. The series contained 32 men between the ages of 39 and 81, and 28 women between 27 and 76. There was a bias towards the older age-groups with 53 per cent of the men and 62 per cent of the women being over 65 years. No patients with heart block following cardiac surgery have been included in this series. Artificial pacing was achieved by means of an electrode catheter passed to the right ventricle from a peripheral vein, the heart being driven by a small adjustable pacemaker (Davies, 1962). Exercise studies were carried out on a bicycle ergometer, electrocardiograms were taken on a Cambridge photographic recorder, and cardiac output was measured by a dye dilution technique using Coomassie blue as described in a previous publication (Sowton, 1964a).

Haemodynamic effects of rapid digitalization following acute myocardial infarction.

Digitalis is now in common use following acute myocardial infarction, and the danger of producing arrhythmias appears to be no greater than in other groups of patients (Askey, 1951). The drug is frequently given intravenously for a rapid effect and to ensure that it will enter the circulation, but little is known of the immediate effects of such administration on the circulation. Malmcrona, Schr6der, and Werko (1966) have reported on 10 patients and we report here our results in a further 11 patients.

THE MANAGEMENT OF HEART BLOCK

In 1952, Zoll described a technique for artificial pacing of the heart. The method employed electrodes placed on the chest wall and electrical impulses of 2 msec. duration at 25-150 volts. Although this indirect technique proved successful in resuscitating and temporarily maintaining life in patients with Stokes-Adams attacks due to asystole, the high voltage required produced skin burns and painful contractions of the muscles of the thorax. Other methods were developed for the direct stimulation of the myocardium with low voltages, and permanent pacing of the heart with small pacemakers is now routinely performed (Bellet et al., 1960; Chardack, Gage, and Greatbatch, 1961; Elmqvist and Senning, 1960; Davies, 1962; Kahn et al., 1960; Landegren, 1962; Lillehei et al., 1960; Stephenson et al., 1959; Weirich et al., 1958; Zoll et al., 1961). Reports on the success of long-term pacing by many different systems have now appeared (Furman et al., 1961; Levitsky et al., 1962; Siddons, 1963). While artificial pacemaking is life saving and permits a return to a normal way of life in most cases, numerous problems have arisen in the maintenance of this artificial system. It is for this reason that we propose to describe our experiences in the management of heart block over the past four years at St. Georges Hospital, of which some have been previously reported by Portal et al. (1962) and Siddons (1963).

Haemodynamic comparisons of atrial pacing and exercise in patients with angina pectoris.

Though exercise is the most physiological test for angina pectoris, it has several disadvantages. The most important are that, it is difficult to achieve a steady state, comparable haemodynamic parameters are not readily reproducible during repeated periods of exercise (Burkart, Barold, and Sowton, 1967), it cannot be used effectively in patients with poor exercise tolerance, and angina pectoris cannot be terminated rapidly. The use of an atrial pacing technique to induce angina pectoris or electrocardiographic changes under safe controlled conditions in patients with coronary artery disease has recently been reported by our own group (Sowton et al., 1967) and others (Lau et al., 1967a, b; Friesinger, Conti, and Pitt, 1967). So far 60 patients have been studied by this technique, and in this paper our results are reported on comparing atrial pacing with an effort test in a group of 16 patients with ischaemic heart disease who were being assessed for possible revascularization surgery. This comparison was made to determine how far the results of the atrial pacing test could be used as part of the clinical evaluation, and the procedures were carefully explained to all patients in advance. In a previous communication we showed that angina occurred at the same tension-time index on repeated pacing runs (Sowton et al., 1967). This index was chosen because it bears some relation to myocardial oxygen consumption in animal experiments (Sarnoff et al., 1958), and it has been used again in the present report. If the concept of a threshold for anginal pain is valid, the maximal myocardial oxygen uptake per minute should be the same no matter how the pain is produced. It seems possible, therefore, that the tension-time index may

Clinical Use of Atrial Pacing Test in Angina Pectoris

Atrial pacing can be used as a safe test in the assessment of patients with angina pectoris. The results are useful in clinical judgements, and this method of investigation may be indicated for patients in whom the diagnosis of angina pectoris is in doubt or who are being considered for surgical treatment of ischaemic heart disease.

THE TRANSMISSION OF ELECTRICAL FORCES FROM THE HEART TO THE BODY SURFACE

The changes in electrical potential at the surface of the body that are recorded as the electrocardiogram are the result of changes in the electrical currents produced by the myocardium. These currents are due to variations in the transmembrane potentials of the muscle fibres during each cardiac cycle. The uneven electrical properties of the tissues in the thorax distort the cardiac electrical forces before they reach the body surface, and these changes must be taken into consideration in the interpretation of the electrocardiogram. The introduction of the bipolar electrode catheter for pacing patients with heart block has provided a known source of electrical activity within the heart which can be compared to the natural myocardial forces. The surface potentials produced by stimuli applied to the bipolar catheter electrode in the right ventricle give an indication of the distortion of the electrical pattern that occurs during transmission of cardiac electrical activity to the body surface. The information obtained in this way is of value in the assessment of the underlying concepts of electrocardiography and vectorcardiography.

Haemodynamic effects of dextro-propranolol in acute myocardial infarction

Intravenous injections of 20-25 mg. d-propranolol did not change the heart rate or systemic pressure in 13 patients with cardiac infarction. Cardiac output was depressed in 10, but there was no clinical deterioration. d-Propranolol was better tolerated than dl-propranolol under these conditions and justifies further investigation as an anti-dysrhythmic agent. The major depressant effects of dl-propranolol following cardiac infarction appear to be due to beta-adrenergic blockade and not to a direct depressant action on cardiac muscle.