SILENT ISCHEMIA IN UNSTABLE ANGINA IS RELATED TO AN ALTERED CARDIAC NOREPINEPHRINE HANDLING

Background. Inferential evidence suggests that silent ischemia might b e related to sympathetic activity. Study of [H-3]norepinephrine kineti cs is a suitable tool to assess the regional sympathetic activity. Thi s method was applied to investigate whether silent myocardial ischemia in unstable angina is related to and depends on cardiac sympathetic o veractivity. Methods and Results. Patients with active unstable angina were compared with patients with inactive unstable angina, stable eff ort angina, and controls. Silent myocardial ischemia was evaluated by three 24-hour Holter monitoring periods on alternate days, and [H-3]no repinephrine kinetics was assessed under rest conditions and following the cold pressor test. Simultaneously, catecholamine concentrations w ere measured in the aortic, coronary sinus, and peripheral venous bloo d. Different than the other groups (p = 0.0013), in patients with acti ve unstable angina, the majority of silent ischemic episodes occurred without increase in heart rate. These patients had a positive coronary sinus-aorta norepinephrine gradient, both at rest and following the c old pressor test. [H-3]Norepinephrine kinetics demonstrated an increas ed selective cardiac spillover, both at rest and, even more, after the cold pressor test. Reduced cardiac [H-3]norepinephrine extraction als o was found. A significant relation was found between the number of is chemic episodes or the overall duration of silent ischemia and norepin ephrine spillover, both at rest and following cold application.Conclus ions. During the acute phase of unstable angina (but not in the quiesc ent phase or in stable effort angina), a disorder in cardiac norepinep hrine handling occurs. This results in a reflex cardiac sympathetic ov eractivity that plays a major role in the occurrence of silent myocard ial ischemia.