Through vasodilation of the coronary arteries and collateral channels, nitrates also improve blood flow to this region of the myocardium. In fact, experimental studies have shown a preferential redistribution of blood to the subendocardium as a result of treatment with nitrates.
Beta-adrenergic receptor blockers competitively inhibit the effects of circulating and neurally released catecholamines at the beta-adrenergic receptors. Their principal effect occurs at the time of adrenergic stimulation when the level of catecholamines is high. By controlling the heart rate and contractility, beta-adrenoreceptor blocking agents decrease the myocardial oxygen requirement at the time of increased sympathetic output (Fig 3). Slower heart rate not only reduces myocardial oxygen consumption, but also leads to a prolonged diastolic phase which has a favorable effect on subendocardial blood flow. buy prednisone
Calcium channel blockers competitively inhibit the entry of calcium into cardiac and vascular smooth muscle cells through voltage sensitive channels. They reduce myocardial oxygen consumption as well as enhance myocardial oxygen delivery (Fig 3). The three commonly used calcium channel blocking agents in the US are nifedipine, diltiazem, and verapamil. They all inhibit calcium influx into smooth muscle cells and cardiac cells causing vasodilation, negative inotropy, chronotropy, and dromotropy (prolonged A-V conduction).