Effects of atropine in patients with bradyarrhythmia complicating myocardial infarction. Usefulness of an optimum dose for overdrive

The effects of 0.4 to 1.5 mg intravenously administered atropine were evaluated in 100 patients with a heart rate <60/min following acute myocardial infarction. Prior to the administration of atropine the mean heart rate was 45 ± 7/min, the incidence of ventricular premature beats was 12 ± 4/min, and two patients had angina. Based on the maximum heart rate response to atropine, the patients were divided into two groups. Heart rate increased to <100/min in 79 patients (group I) and {succeeds above single-line equals sign} 100/min in 21 patients (group II). Ventricular premature beats decreased significantly (p < 0.01) in both groups; (2 ± 4/min in group I and 2.4 ± 0.8 in group II). In only one patient in group II did ventricular premature beats first appear following the administration of atropine. Blood pressure did not change significantly after the administration of atropine in either group. In two patients (group I), angina disappeared and in two others (group II) angina appeared following the administration of atropine. Doseheart rate analysis revealed that 70 per cent of the patients in group II and only 17 per cent of those in group I received {succeeds above single-line equals sign}0.8 mg atropine (p < 0.01). There was a statistically significant correlation between the dose of atropine and the increment in heart rate (r = 0.41, p < 0.01). Thus, a relatively lower dose of atropine (<0.8 mg) had a beneficial antiarrhythmic effect. Higher dosage caused an inappropriate tachycardia, angina and ventricular premature beats, and should be avoided.