Which of the following classes of medications protects the ischemic myocardium by blocking catecholamines and sympathetic nerve stimulation?
A. Beta-adrenergic blockers
B. Calcium channel blockers
C. Narcotics
D. Nitrates
Correct Answer: A. Beta-adrenergic blockers
Beta-adrenergic blockers work by blocking beta receptors in the myocardium, reducing the response to catecholamines and sympathetic nerve stimulation. They protect the myocardium, helping to reduce the risk of another infarction by decreasing myocardial oxygen demand. Beta-blockers also decrease blood pressure via several mechanisms, including decreased renin and reduced cardiac output. The negative chronotropic and inotropic effects lead to a decreased oxygen demand; that is how angina improves after beta-blocker usage.
Option B: Calcium channel blockers reduce the workload of the heart by decreasing the heart rate. The non-dihydropyridines have inhibitory effects on the sinoatrial (SA), and atrioventricular (AV) nodes are resulting in a slowing of cardiac conduction and contractility. This allows for the treatment of hypertension, reduces oxygen demand, and helps to control the rate in tachydysrhythmias.
Option C: Narcotics reduce myocardial oxygen demand, promote vasodilation, and decrease anxiety. There are three opioid receptors: mu, kappa, and delta. Mu receptors mediate most of the clinical and adverse effects of opioids: analgesia, sedation, euphoria, constipation, and respiratory distress. Activation of kappa receptors also leads to analgesia, dyspnea, and sedation.
Option D: Nitrates reduce myocardial oxygen consumption by decreasing left ventricular end-diastolic pressure (preload) and systemic vascular resistance (afterload). The venodilation increases the venous capacitance and lowers the preload; this subsequently lowers the left ventricular end-diastolic pressure, resulting in a reduction in myocardium workload, which decreases the oxygen demand of the heart.
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