Effect of nitroglycerin on cardiovascular function at fixed and at variable heart rate.

Studies were carried out on 23 patients divided into 2 groups: Group 1. 14 consecutive patients with complete heart block were studied, whose ages ranged from 55 to 76 with a group average of 70-2 years. Aetiology of the heart block in 8 patients was considered to be coronary artery disease, as judged by clinical and laboratory evidence. In 6, all of whom developed block past age 50, no probable oetiology could be assigned. Of the 14 patients, 8 had the wires of a fixed rate permanent pacemaker (Chardack-Greatbatch) implanted in the free wall of the left ventricle; in the remaining 6 the heart was stimulated by means of a bipolar electrode catheter placed in the right ventricle and connected to an external pacemakert (Model TR-3). Group 2. 9 patients with normal sinus rhythm were studied: 4 had coronary disease, 1 had essential hypertension, and 4 had no evidence of heart disease. Their ages ranged from 45 to 72 years with a group average of 60 years. Cardiac output was determined with the indicator-dilution technique using indocyaninet (Cardiogreen) as an indicator. Details of this technique were described in a previous report (Benchimol et al., 1963). The indicator was rapidly injected into the left cubital vein with sampling from the brachial artery through a No. 18 Cournand needle. A Gilford cuvette densitometer§ (Model 103 IR) was used to detect the injected dye. The curves were recorded in the Electronics for Medicine oscilloscopic photographic recorder** (Model DR-8) at a paper speed of 5 mm./sec. The cardiac output was calculated with the Stewart-Hamilton method in 14 patients. In the remaining 9 the output of the densitometer was coupled with a dye-dilution