Reflected pressure waves in the ascending aorta: effect of glyceryl trinitrate.

Reflected pressure waves returning to the ascending aorta are an important contribution to aortic systolic pressure and thus the load on the left ventricle. The effect of glyceryl trinitrate on pressure wave reflections in the ascending aorta was studied using the transmission of arterial pressure between two high fidelity pressure transducers. Glyceryl trinitrate 0.3 mg sublingually reduced systolic arterial pressure by 11 mmHg owing to a reduction of the late systolic pressure peak. Mean arterial pressure fell 2 mmHg, but heart rate and aortic flow did not change. The aortic input impedance was reduced at the first harmonic (control 18.4(4.1); glyceryl trinitrate 10.8(2.4) kPa.s.litre-1; p less than 0.005) but characteristic impedance was not changed (control 12.7(3.8); glyceryl trinitrate 14.2(3.3) kPa.s.litre-1). The first two harmonics of apparent phase velocity were reduced by glyceryl trinitrate (1.05 Hz: control 3314(798); glyceryl trinitrate 1772(495) cm.s-1; p less than 0.01; 2.1 Hz: control 1246(269); glyceryl trinitrate 754(127) cm.s-1; p less than 0.05), yet the foot to foot wave velocity was unchanged (control 688(112); glyceryl trinitrate 726(112) cm.s-1). There was a significant reduction in the amplitude of the global reflection coefficient at 1.05 Hz (control 0.70(0.09); glyceryl trinitrate 0.48(0.08); p less than 0.001) and at 2.1 Hz (control 0.48(0.07); glyceryl trinitrate 0.23(0.06); p less than 0.005) with no significant change in phase. Glyceryl trinitrate reduces cardiac pulsatile load by diminishing the amplitude of wave reflections arriving back in the aorta during systole yet has no effect on aortic compliance or arteriolar resistance. This study demonstrates a method of evaluating the effect of vasoactive drugs on cardiac pulsatile load.

Exercise stress testing in the post-myocardial infarction patient.

Recent studies indicate that predischarge evaluation of the post-myocardial infarction (MI) patient is important in predicting their subsequent course and the need for specific treatment. Left ventricular function, residual ischemia and the tendency toward ventricular arrhythmias can all be assessed noninvasively in the late hospital phase. Stress testing is 1 of the most useful and widely available of these techniques. An impaired hemodynamic response to exercise expressed by excessive tachycardia, plateau or falling blood pressure or reduced work load capacity suggests an increased risk of recurrent cardiac events in the near future. Angina or electrocardiographic abnormalities, including arrhythmias, also indicate a less favorable outcome. A good performance in a post-MI stress test is associated with a relatively good prognosis. The exercise electrocardiogram, therefore, appears to be a useful screening device for evaluating post-MI patients. Other noninvasive tests such as radionuclide ventriculography, exercise thallium scanning, Holter monitoring and echocardiography greatly augment the predictive value of exercise electrocardiography, and a patient profile should be developed using all the available clinical and laboratory data. Patients with a poor prognostic profile may then undergo further testing, such as coronary angiography, and their subsequent therapy modified appropriately.

Differences between the effects of practolol and propranolol on the diastolic properties of the left ventricle.

To elucidate the mechanism by which left ventricular and diastolic pressure (LVEDP) is reduced by practolol, ventricular volumes, hemodynamics, and diastolic elastic stiffness were determined before and 10 min after intravenous practolol (400 mug/kg) in 12 patients. Heart rate decreased in all patients after practolol (avg., --9/min, p less than 0.02). There was an insignificant increase in stroke work index and decrease in cardiac index attributable to the fall in rate. Practolol did not change and diastolic volume or ejection fraction, but the average LVEDP fell from 21 to 15 mm Hg (p less than 0.01) which was sustained even with atrial pacing to prepractolol heart rates. Diastolic elastic stiffness was also reduced after practolol (0.665 to 0.593, p less than 0.0025). The data indicate that practolol exerts a negative chronotropic effect on the intact heart and, in contrast to other beta blockers such as propranolol, appears to decrease diastolic stiffness in the left ventricle.