Effect of isoprenaline and propranolol on left ventricular function as determined by nuclear angiography.

We have studied changes in left ventricular function with non-invasive nuclear angiography, at rest, during graded infusions of isoprenaline (0.75, 1 0, and 2-0 jig/min), and 10 minutes after a single intravenous injection of propranolol (0-25 mg/kg).Totest the adequacy of beta-adrenoreceptor antagon- ism, isoprenaline (2.0 vg/min) was reinfused after propranolol.Eight healthy subjects have been studied.Ventricular volume-time curves were obtained by electrocardiogram-gated accumulation of count rates in sequential 20 ms time bins (over 500 cardiac cycles) from a selected region of interest corresponding to the left ventricular blood pool.99mTc-HSA was used as the radiopharmaceutical.In addition to the ejection fraction, the mean ejection rate, peak rate of change of volume in systole and diastole, and the mean ejection and filling times were calculated from these volume-time curves.A linear dose dependance has been shown in the changes in ejection fraction, mean ejection rate, peak rate of change of volume in systole, and mean ejection time.After beta-adrenoreceptor antagonism the resting values of various variables were not significantly different from the control values, except for the mean ejection rate.Reinfusion of isoprenaline after beta-adrenoreceptor antagonism was without effect on any of the variables.This study shows that nuclear angiography provides a satisfactory non-invasive technique for the evaluation of cardiac function, especially when physiological and pharmacological interventions are examined.Changes in ventricular volume can be measured at nuclear angiography by imaging a suitably labelled blood pool within the heart using a gamma camera system.The electrocardiogram-gated accumulation of radioactivity in sequential time bins yields an activity-time curve from which complementary variables of ventricular function may be measured.Since count rates within the region being sampled are proportional to volume, it is implied that such activity-time curves represent proportional volume change.A good correlation between the ejection fraction measured by this technique and that measured by contrast cineangiography has been reported earlier from this laboratory' and also by other workers.2-4A distinct advantage of this method is that repeated measurements can be made *Visiting Commonwealth Fellow.