Sixty patients undergoing coronary artery bypass surgery were studied prospectively in order to investigate the effect of a cardioselective beta-blocker on the incidence of postoperative supraventricular arrhythmias. Patients with good left ventricular function were randomly divided into two groups: 30 patients treated with atenolol and 30 patients acting as controls. Atrial fibrillation was seen in 11 patients and frequent premature atrial extrasystoles were noted in one. Eleven (37%) patients in the control group experienced arrhythmias whilst atenolol significantly reduced this incidence to 3% (one patient), P = 0.001. There was no significant relationship between the development of supraventricular arrhythmias and the following variables: age, sex, severity of preoperative symptoms, previous myocardial infarction, extent of coronary artery disease, technique of myocardial preservation used, ischaemic time, number and site of saphenous vein grafts, endarterectomies performed and perioperative serum potassium levels. It is concluded that the use of atenolol (started 72 h before operation) is effective in reducing the incidence of supraventricular arrhythmias following elective coronary artery bypass operations in patients with good left ventricular function.

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The dietary supplement ephedra is a potent sympathomimetic that was banned by the US Food and Drug Administration in 2003 because of its deleterious effects on cardiovascular function and thermoregulation during exercise. Unfortunately, extracts of ephedra can still be obtained via the internet and are in use worldwide. The horse is the only athletic species other than humans that sweats to thermoregulate and it controls cardiovascular function in a similar fashion. The purpose of this study was to use the horse to examine the acute effects of ephedra (Ma Huang) to investigate on markers of performance as well as effects on cardiovascular function and thermoregulation during acute exercise. Six Standardbred mares (~450 kg; 6-12 years of age) were used in a crossover design consisting of a ephedra (Ma Huang containing 8% ephedra alkaloid) and control (applesauce) group. All horses performed an incremental graded exercise test (GXT) at a 6% fixed grade to measure oxygen uptake (VO2), run time, velocity at VO2max, maximal velocity, recovery time, haematocrit, total plasma protein concentration, heart rate, right ventricular pressure (RVP), pulmonary arterial pressure (PAP), rectal temperature and recovery. Measurements were recorded at rest, during exercise and post 2 and 5 min recovery. There was a difference (P<0.05) in pre-exercise haematocrit but not in any other haematocrit or plasma protein sampling intervals. VO2 was greater (P<0.05) for the ephedra group before exercise, at each step of the GXT, at VO2max, and during recovery compared to the control group. Recovery time was significantly different, but run time was not (P≯0.05). Heart rate was elevated (P<0.05) at 2 and 5 min recovery in horses administered ephedra. Significant differences were observed for RVP and PAP and rectal temperature during recovery. Recovery score (sweating response, respiration rate, behaviour) was altered (P<0.05) by ephedra administration. These data suggests an increase in energy expenditure and thermogenesis when horses consume ephedra. However, markers of performance (run time, velocity at VO2max, and maximal velocity completed) were not altered by ephedra administration.

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