Coronary vasomotor and therapeutic influences of propranolol and nifedipine on the spontaneous component of mixed angina

In 24 patients with spontaneous and effort-related angina (mixed angina), propranolol (80 mg q.i.d.) was significantly more beneficial than nifedipine (20 mg q.i.d.) on the number, duration and severity of the spontaneous manifestations. In some cases nifedipine elicited a paradoxical response. These patterns are unlikely to have resulted from different influences on the myocardial oxygen demands, since heart rate was steady before the occurrence of ischaemia and systemic arterial pressure was equally reduced in all patients. Sublingual nifedipine (10 mg) was tested in 12 patients and the residual lumen diameter of significant (greater than 50%) coronary stenoses (quantitative angiography) was unchanged in one, enhanced in seven and reduced in four of them. Lumen variations ranged from +1.59 to -1.2 mm and correlated closely with the results of oral nifedipine treatment. Propranolol (0.1 mg kg-1 i.v.) was tested in the other 12 cases and in none did variations of stenosis lumen diameter exceed 0.3 mm. These observations indicate that: in a number of lesions a portion of pliable wall may offer a compliant substrate for vasomotor influences; this may be the major factor whereby coronary obstructions cause spontaneous, besides effort-related angina; nifedipine is effective on the former manifestation provided that it does not promote stenosis constriction; propranolol may result in benefit through bradycardia facilitating coronary flow in diastole and reducing the baseline metabolic demands, to elevate the threshold of ischaemia during transient impedance to flow.