Effects of Ranolazine on Coronary Flow Reserve in Symptomatic Diabetic Patients and CAD

Ranolazine is a novel anti-anginal agent which inhibits the late sodium current in cardiomyocytes, decreasing sodium and calcium overload. In ischemia, excess of intracellular calcium may impair myocyte relaxation and contribute to ventricular diastolic stiffness, which in turn affects myocardial contractility and perfusion. Ranolazine is FDA-approved for treatment of chronic angina. In three randomized, placebo-controlled trials of patients with stable angina, it was shown to increase exercise time free of angina and ST-segment depression, increase exercise capacity and decrease angina when used in combination with established antianginal agents including diltiazem, amlodipine or atenolol, and reduce the frequency of angina on patients on maximum doses of amlodipine.Similarly, in a large population of patients with acute coronary syndromes, ranolazine also decreased exertional angina symptoms and incidence of arrhythmias, with no effect on mortality. Interestingly, in this same study, it significantly improved hemoglobin A1c and recurrent ischemia in patients with diabetes mellitus, and reduced the incidence of increased hemoglobin A1c in patients without known prior hyperglycemia. Although the anti-ischemic effect of ranolazine is thought to be mediated in part by increased myocardial blood flow,there is currently limited evidence for such an effect on tissue perfusion. A previous study in women without overt CAD did not detect improved myocardial blood flow after treatment with ranolazine. In that study, however, coronary hyperemia was elicited with adenosine (which uncouples blood flow from cardiac work, and reflects predominantly endothelial-independent vasodilation) rather than exercise, which triggers a more complex interplay between metabolic demand, coronary hemodynamics, and vasodilator response. Thus, there is a need for additional investigation of whether the beneficial effects of ranolazine on exertional symptoms are directly related to improved global tissue perfusion. Such evidence would support the use of ranolazine as an anti-ischemic therapy in the challenging population of symptomatic patients with evidence of microvascular dysfunction without obstructive CAD.