Effect of early administration of atropine on paradoxic sinus deceleration during dobutamine stress echocardiography

Dobutamine stress echocardiography (DSE) is a well-established, safe, and reliable technique for diagnosis of coronary artery disease. The generally accepted protocol for DSE involves infusion of increasing doses of dobutamine from 5 to 40 g/kg/min at 3-minute intervals. In about 1/3 of patients, however, target heart rate cannot be achieved by the administration of dobutamine alone. Failure to achieve an adequate heart rate during DSE is attributed to the use of -adrenergic blocking agents, chronotropic incompetence, or paradoxic sinus deceleration (PSD). PSD is characterized by an initial increase followed by a significant decrease in heart rate during incremental doses of dobutamine. This is believed to result from activation of the cardioinhibitory reflex (Bezold-Jarisch reflex) through left ventricular sensory receptors. Although suggested by some, it is unclear whether left ventricular inferoposterior wall ischemia is the trigger for PSD. In the present study, we sought to identify the characteristics of patients with PSD during DSE and to determine whether early administration of atropine could prevent its development. • • • The study population consisted of 114 consecutive patients (age 36 to 91 years [66 12]; 66 women [58%]) with suspected coronary artery disease who were referred for DSE between March and June 2000. Patients were prospectively randomized into 2 protocols. Group A (n 55) underwent standard DSE protocol, consisting of incremental doses of dobutamine from 5 to 40 g/kg/min at 3-minute intervals, and if needed, up to 1 mg of atropine (0.25 mg doses at 2-minute intervals) at the completion of the 40 g/kg/min dose of dobutamine. A 3-minute infusion of dobutamine at 50 g/kg/min was given if necessary at peak (n 2). Patients in group B (n 59) underwent the same protocol except for administration of atropine at completion of the 10 g/kg/min dose of dobutamine with the aim to increase heart rate by 25% before advancing to the next dose of dobutamine. Atropine was not administered if the patient had a specific contraindication. End points for DSE termination were: (1) attainment of target heart rate, (2) completion of stress protocol, (3) echocardiographic evidence of ischemia, or (4) development of significant arrhythmia, hypertension, hypotension, or intolerable symptoms. A standard echocardiographic image acquisition protocol was used and heart rate was recorded from 12-lead electrocardiograms performed at 1-minute intervals. DSE was considered positive for ischemia if any worsening in left ventricular wall motion developed during the test except for a change from akinesia to dyskinesia. PSD was defined as a reduction in heart rate of 5 beats/min lasting for 3 minutes at dobutamine infusion rates of 10 g/kg/min. Data are presented as mean SD and numbers and percentages. Differences between continuous variables were assessed with the unpaired Student’s t test. Chi-square or Fisher’s exact test compared proportions. No statistically significant differences were noted between the 2 groups with regard to age, sex, baseline heart rate, blood pressure, and left ventricular ejection fraction, as well as risk factors for coronary artery disease (Table 1). Similarly, the number of patients who were on -adrenergic blocking agents was not significantly different in the 2 groups (28 [52%] vs 35 [59%], p NS) (Table 1). An equal proportion of the patients in the 2 groups (73%) reached target heart rate ( 85% predicted maximum heart rate for age). In addition, DSE was terminated in 7 patients (13%) in group A and 6 patients (10%) in group B due to myocardial ischemia (p NS). Coronary angiography was performed within 1 month of DSE in 9 of these 13 patients (5 in group A and 4 in group B) and showed significant coronary artery disease ( 50% luminal narrowing in 1 major epicardial coronary artery) in all patients. Safety considerations were the reasons for termination of DSE in 6 patients (11%) in group A and 2 patients (3%) in group B (p NS). The remaining 2 patients (3%) in group A and 8 patients (14%) in group B did not reach target heart rate despite maximal doses of dobutamine and atropine (if not contraindicated) (p NS). Five of the 8 patients in group B who did not reach target heart rate were taking -adrenergic blocking agents, From the Department of Medicine, Division of Cardiology, Albert Einstein College of Medicine, Bronx, New York. Dr. Shirani’s address is: Jack D. Weiler Hospital of the Albert Einstein College of Medicine, Division of Cardiology, 1825 Eastchester Road, Bronx, New York 10461-2373. E-mail: jshirani@montefiore.org. Manuscript received August 6, 2001; revised manuscript received and accepted October 31, 2001.