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Effects of beta-adrenergic blockade in acute myocardial infarction: evaluation by radionuclide ventriculography
M W Kronenberg1, J T Beard, S M Stein
1Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee.
Insights
Beta-adrenergic blockade in acute myocardial infarction patients reduced left ventricular contractility and right ventricular performance. This beta-blockade further depressed cardiac function, as measured by the pressure/volume ratio.
Area of Science:
- Cardiology
- Pharmacology
- Physiology
Background:
- Beta-adrenergic blockade's effect on left ventricular contractility in acute myocardial infarction is debated, with potential for depression or improvement via ischemia reduction.
- Assessing left ventricular contractility requires reliable indices, especially in the context of acute cardiac events.
Purpose of the Study:
- To evaluate the impact of intravenous metoprolol on left ventricular contractility in patients with acute myocardial infarction.
- To assess changes in cardiac performance using the pressure/volume (P/V) ratio as an index of contractility.
Main Methods:
- Employed gated equilibrium radionuclide ventriculography and cuff blood pressure measurements.
- Assessed the left ventricular systolic pressure/volume (P/V) ratio in 10 patients before and after metoprolol administration.
- Compared patient data with 13 healthy subjects for baseline reference.
Main Results:
- Patients with acute myocardial infarction exhibited lower baseline P/V ratio and left ventricular ejection fraction (LVEF) compared to normal subjects.
- Following metoprolol, systolic blood pressure decreased, and left ventricular end-systolic volume increased, significantly reducing the P/V ratio (1.7 to 1.4).
- Left ventricular ejection fraction remained unchanged, but right ventricular ejection fraction (RVEF) significantly decreased (50% to 43%) post-metoprolol.
Conclusions:
- Radionuclide ventriculography confirmed reduced left ventricular contractility in acute myocardial infarction.
- Intravenous metoprolol further decreased left ventricular contractility and impaired right ventricular performance in these patients.
Abstract:
In acute myocardial infarction, beta-adrenergic blockade might depress left ventricular contractility or improve contractility by reducing ischemia. Gated equilibrium radionuclide ventriculography and cuff blood pressure were employed in 10 patients to assess the left ventricular systolic pressure/volume (P/V) ratio as an index of contractility before and after intravenous metoprolol 9.3 +/- 2.5 hr after onset of infarction. In 13 normal subjects, the baseline left ventricular PV ratio was 3.5 and the left ventricular ejection fraction (LVEF) was 70%, both greater than the patients with infarction. In the patients after blockade, the systolic blood pressure decreased (p = 0.02), and the left ventricular end-systolic volume increased (p = 0.003), thus decreasing the P/V ratio from 1.7 to 1.4 (p = 0.003), while the ejection fraction (EF) was unchanged (55% versus 52%). The right ventricular ejection fraction (RVEF) decreased from 50% to 43% (p = 0.004). Thus, radionuclide ventriculography demonstrated that left ventricular contractility was reduced in patients with acute myocardial infarction and that beta-adrenergic blockade further decreased left ventricular contractility and right ventricular performance.