Clinical assessment of beta blockade

This study was undertaken to assess a clinical measurement (leg squats) in order to determine the adequacy of beta-adrenergic blockade (AdBB) utilizing the symptom-limited exercise test heart rate of less than 120 beats/min as the standard. Seventy subjects were tested, 35 receiving beta-adrenergic-blocking drugs in clinically determined maximal doses, and 35 subjects not receiving these agents. Sensitivity (Se), specificity (Sp), and positive (Pv+) and negative (Pv-) predictive values were calculated for post-leg squat heart rates of less than or equal to 100, less than or equal to 110 and less than or equal to 120 beats/min. Other variables analyzed for AdBB were resting heart rates and post-leg squat heart rate increase greater than 50% over baseline. A cost-benefit analysis was also performed. It was concluded that: (1) Neither the resting heart rate or percent increase in heart rate compared to baseline reliably predicted AdBB. (2) In patients receiving beta-blocking drugs, a post-squat heart rate of less than or equal to 100 beats/min had a Se = .82, Sp = .67, Pv+ .70, and Pv- .80, values not high enough to be reliably used in many clinical situations. (3) If the post-squat heart rate was greater than 110 beats/min, however, AdBB is probably absent, since no subjects on beta blockers with maximum exercise test heart rate less than or equal to 120 beats/min had a post-leg squat heart rate greater than 110 beats/min. (4) For a reasonable range of cost and test performance estimates, utilization of the leg squat test as described here is favored on the basis of cost-benefit analysis.