Evaluation of the efficacy of routine preoperative electrocardiograms.

OBJECTIVE: To evaluate the efficacy of routine preoperative electrocardiograms (ECG) in predicting perioperative cardiovascular complications in an essentially healthy population. DESIGN: Retrospective chart review. SETTING: The adult hospital of a large academic medical center. PARTICIPANTS: One thousand ASA class I and II adult patients undergoing a number of different elective surgical procedures. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The mean age of the population was 48 years (range, 18 to 88), and 53% were female. Fifty-seven percent of the population had a preoperative ECG, of which 56.5% were considered normal, 37.8% were abnormal, and 6.6% were considered borderline. Twenty-seven percent of the population presented with cardiovascular risk factors, and of these, 93.2% had an ECG performed. Seventy-three percent of patients had no cardiovascular risk factors, and of these, 44.5% had a preoperative ECG. Patients who had cardiovascular risk factors had significantly more abnormal ECGs than those without (51% v 26.1%,); however, there was no difference in the prevalence of perioperative events between the two groups. The positive predictive value of an abnormal ECG for a perioperative event was slightly greater for patients with cardiovascular risk factors than for those without (42.7% v 34.7%, respectively); however, this difference was not significant. In addition, a normal ECG was just as predictive as an abnormal one. CONCLUSIONS: Results of this study suggest that the practice of routine ECG screening for patients with no cardiovascular risk factors is a poor predictor of perioperative complications in this patient population. A review of the current criteria for ordering preoperative ECGs may reduce the number of unnecessary tests and improve cost-effectiveness.

Calcium: its role in alpha 1-adrenergic stimulation of atrial natriuretic peptide secretion.

alpha 1-Adrenergic agonists increase atrial natriuretic peptide (ANP) secretion. The mechanism of alpha 1-adrenergic-stimulated secretion is not known. In this study we examine the calcium dependency of alpha 1-agonist-stimulated ANP secretion. Isolated superfused rat left atria paced at 2 Hz were used for study. Superfusion with 10 microM phenylephrine increased ANP secretion by 2-fold. Lowering the superfusate calcium concentration from 1.8 to 0.2 mM totally negated the secretory response to phenylephrine. To determine whether this reflected a reduction in calcium influx, reduced calcium release from the sarcoplasmic reticulum (SR), or both, atria were superfused with 1 microM ryanodine, an inhibitor of SR calcium release. Ryanodine had no effect on phenylephrine-stimulated ANP secretion. Atria were superfused with 10 microM nitrendipine to determine whether calcium influx through voltage-dependent calcium channels was a mechanism of calcium entry for stimulation. Nitrendipine inhibited phenylephrine-stimulated ANP secretion by 49% without interfering with alpha 1-adrenergic antagonist receptor binding. This finding was supported by the observation that phenylephrine-stimulated secretion was 52% lower in nonbeating atria. alpha 1-Adrenergic agonists have been reported to enhance Na-H antiporter activity. To determine whether the resulting rise in intracellular sodium may alter Na-Ca exchange to raise intracellular calcium levels, atria were superfused with the Na-H antiporter inhibitor, 5-(N,N-hexamethylene)amiloride. Superfusion with 25 microM 5-(N,N-hexamethylene)amiloride did not inhibit phenylephrine-stimulated ANP secretion. Lastly, the calcium dependency of the maintenance of an established response to phenylephrine was examined. Atria were superfused with phenylephrine in buffer containing 1.8 mM calcium for 45 min, followed by superfusion with phenylephrine in 0.2 mM calcium for 30 min. There was no fall in phenylephrine-stimulated secretion by atria superfused in 0.2 mM calcium. In contrast, addition of the alpha 1-adrenergic antagonist phentolamine induced an immediate fall in phenylephrine-stimulated ANP secretion. We conclude that 1) calcium influx is necessary to initiate alpha 1-agonist-stimulated ANP secretion; 2) calcium release from the SR does not play a role in alpha 1-agonist-stimulated secretion; 3) calcium entry through L-type calcium channels is responsible for half of the calcium influx; 4) enhanced Na-H antiporter activity does not play a role in alpha 1-agonist-stimulated secretion; and 5) maintenance of alpha 1-agonist-stimulated secretion is not dependent on calcium influx.