Sustained slow heart rates in men of middle age or older who have coronary heart disease, hypertension, or pulmonary disease may be evidence of underlying disease of the cardiac pacemaker and of increased risk of sudden cardiac death. In a seven-year prospective study of 301 men, those whose mean heart rates did not rise as expected during a day's activities, who had a low peak rate response to standard exercise, and who showed little evidence of phasic variation in heart rate with respiration, and no evidence of the random abrupt sinus slowing that occurs with sighing, coughing, or straining, often had overt abnormalities of their cardiac pacemakers (eg, wandering atrial pacemaker, atrioventricular [A-V] junctional rhythm, "coronary sinus rhythm") or developed these later. They experienced significantly more sudden cardiac deaths than expected (P <.005).
Hinkle LE, Carver ST, Plakun A. Slow Heart Rates and Increased Risk of Cardiac Death in Middle-Aged Men. Arch Intern Med. 1972;129(5):732-748. doi:10.1001/archinte.1972.00320050056006