HAeMODYNAMIC STUDIES IN PATIENTS WITH ARTIFICIAL PACEMAKERS

Abstract

The treatment of complete heart block by means 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. al., 1963). Preliminary studies showed that under constant conditions with patients at rest five measurements of relative cardiac ouput could be made with results that differed by 7 per cent or less. During the determination of output-time curves cardiac output measurements were made at two-minute intervals: during the determination of rate-output curves the output was measured four minutes after each alteration in pacemaker rate. Conversion of relative output to litres/min. was made by calibration of the first curve by means of control and end-tail blood samples: the absolute values are approximate.Resting measurements were made when the patients were sitting with the trunk supported at about 45 degrees. Exercise studies were carried out on a bicycle ergometer (Gabe and Robinson, 1960), on which the power setting could be varied in steps of 5 Watts. Table I gives the approximate oxygen uptake (B. Robinson, 1963, personal communication) and equivalent activity of various settings on this apparatus.

Cardiovascular Dynamics in Man During Idioventricular Rhythm and at Various, Electrically Determined, Ventricular Rates in, Acquired Complete Heart Block at Rest

“…The observation of a low cardiac output at idioventricular rates and, with individual exceptions, of an 'optimal' cardiac output at the ventricular rate o f about 80/min with inversion of trend be yond this value has been the general experience [2,5,7]. At this rate the mean cardiac output generally becomes normal [2,3,5], although in the present series and in the report by S a m e t and co authors [4] it remained subnormal.…”

“…The cardiovascular dynamics at different ventricular rales at rest in patients with complete heart block (CIIB) have been the object o f much recent investigation [1][2][3][4][5][6][7]28]. With two exceptions [2,5], cardiac output has been measured by the dye dilution technique and information on the rate-dependent changes of oxygen uptake and arterio-venous oxygen difference is scarce.…”

Value of pacing in cardiac failure associated with chronic atrioventricular block.

“…Such studies of patients with uncomplicated atrioventricular block show a variable change in cardiac output which may frequently increase by more than 50 per cent with pacing. The change in cardiac output, however, is dependent (Sowton, 1964). In retrospect it seems likely that the patients studied in this series, who had severe heart failure, were perhaps paced at a rate in excess of the optimum for a maximum reduction in filling pressure and rise in cardiac output.…”

“…The haemodynamic effects of pacing in chronic atrioventricular block and in particular the effect on cardiac output have been examined in a number of studies (Samet et al, 1964;Sowton, 1964;Bevegard et al, 1967). Such studies of patients with uncomplicated atrioventricular block show a variable change in cardiac output which may frequently increase by more than 50 per cent with pacing.…”

Experimental myocardial infarction

“…In the presence of elevated filling pressure in animals (6) or complete heart block and congestive failure in patients, increasing the cardiac rate may improve cardiac output (11,12). Conversely, angina pectoris and acute left ventricular failure may be precipitated by induced tachycardia in some patients with coronary artery disease (13,14 (19,20).…”