Admission serum potassium in patients with acute myocardial infarction: its correlates and value as a determinant of in-hospital outcome.

STUDY OBJECTIVES: Although controversial, hypokalemia (LK) in patients with acute myocardial infarction (MI) is thought to predict increased in-hospital morbidity, particularly cardiac arrhythmias, and mortality. Also, the mechanism of low serum potassium in the setting of MI has not been delineated. We evaluated the frequency, attributes, and outcome, and speculated on the mechanism of LK in patients with MI. DESIGN: This was a prospective cross-sectional study of 517 consecutive patients with MI admitted to the coronary care unit (CCU). Serum potassium was measured in the emergency department and repeatedly thereafter throughout hospitalization, and was used in the analysis, along with a large array of clinical and laboratory variables. RESULTS: The patients were allocated to a LK and a normokalemic (NK) cohort, based on the emergency department serum potassium measurement. The 41 patients with LK (3.16+/-0.24 mEq/L; 7.9% of total) were comparable on admission in their baseline assessment to the 476 patients with normal serum potassium (4.28+/-0.56 mEq/L), except for lower emergency department magnesium (1.48+/-0.15 mg/dL vs. 1.96+/-0.26 mg/dL; p = 0.0005) and earlier presentation after onset of symptoms (3.0+/-4.1 h vs. 4.4+/- 6.2 h; p = 0.05). There was a poor correlation between serum potassium and magnesium on admission (r = 0.14). Peak creatine kinase (CK) and myocardial isomer of CK were higher in the LK patients (3,870+/-3, 840 IU/L vs. 2,359+/-2,653 IU/L [p = 0.018] and 358+/-312 IU/L vs. 228 +/- 258 IU/L [p = 0.013], respectively). Management of the two cohorts was the same, except for a higher rate of use of magnesium (14.6% vs. 4.6%; p = 0.007), serum potassium supplements (90.2% vs 43. 1%; p = 0.000005), and antiarrhythmic drugs (78.0% vs 50.4%; p = 0. 0007) in the LK patients. No difference was detected between the LK and NK patients in total mortality (24.4% vs. 18.3%; p = 0.34), cardiac mortality (17.1% vs. 15.3%; p = 0.52), atrial fibrillation (14.6% vs 13.9%; p = 0.89), and ventricular tachycardia (22.0% vs. 16.0%; p = 0.32), but ventricular fibrillation (VF) occurred more often (24.4% vs 13.0%; p = 0.04) in the LK patients. However, proportions of VF occurring in the emergency department, CCU, or wards in the two cohorts were not different, but they were higher during the time interval prior to emergency department admission in LK patients (17.1% vs 2.1%; p = 0.00001). CONCLUSIONS: LK is seen in approximately 8% of patients with MI in the emergency department; LK is associated with low emergency department magnesium, and low serum potassium levels in the CCU and throughout hospitalization. LK has no relationship to preadmission use of diuretics, it is associated with early presentation to the emergency department, and it is not a predictor of increased morbidity or mortality.

Correlates and in-hospital outcome of painless presentation of acute myocardial infarction: a prospective study of a consecutive series of patients admitted to the coronary care unit.

BACKGROUND: The past literature has long ago identified painless myocardial infarction as a clinical entity; however, the term has been applied, often loosely, to denote diagnosis of infarction made at autopsy, or during routine electrocardiography, or at presentation with atypical symptoms. Many of the old studies were retrospective or included patients who could not contribute a reliable history. METHODS: Systematic interviews of 517 consecutive patients with an acute myocardial infarction admitted to the Coronary Care Unit were carried out; a large array of data was collected prospectively while the patients were taken care of in the hospital. RESULTS: A reliable history of symptoms at the inception of the clinical episode could be provided by 501 patients; 40 patients (8.0%) presented with painless (not silent) infarction, while the remaining 461 had pain. Multivariate analysis revealed that painless presentation of myocardial infarction correlated positively with age (OR 1.05, CI 1.02-1.08) and admission Killip class (OR 2.58, CI 2.16-2.97), and negatively with history of prior angina (OR 0.16, CI 0.15-064); also it was not a predictor of increased rate of mortality or life-threatening arrhythmias. CONCLUSIONS: Presentation with painless myocardial infarction occurs in older patients with increased degrees of pulmonary congestion on admission, and less frequent rate of prior angina than the ones encountered in patients with pain; however such presentation is not an independent predictor of worse than expected in-hospital outcome.

Comparative pharmacodynamics and pharmacokinetics of conventional and long-acting propranolol.

This investigation was conducted to compare the pharmacokinetic and pharmacodynamic effects of single and multiple doses of conventional propranolol and long-acting propranolol in healthy human volunteers. Two double-blind, randomized, double-crossover, Latin square studies were carried out. One study evaluated long-acting propranolol 160 mg/d, conventional propranolol 40 mg qid, or placebo for seven days in 24 men. The other study compared long-acting propranolol 80 mg/d, conventional propranolol 20 mg qid, or placebo for seven days in 27 men. At specific times after the administration, blood samples were obtained, and heart rate and blood pressure were measured; exercise tests were done both on the first day and at steady state (day 7). In both studies, the area under the plasma propranolol concentration-time curve and the peak concentration were significantly less (P less than .0001) after the administration of long-acting propranolol compared with conventional propranolol on both day 1 and day 7; in addition, the elimination half-life was longer after administration of the long-acting preparation (9 hr) compared with that following the conventional dosage form (4 hr). Both conventional and long-acting propranolol significantly decreased the exercise heart rate at each of the selected time points (P less than .05) compared with placebo. Reduction in exercise heart rate was greater with conventional propranolol than with the long-acting formulation, but the differences were not statistically significant, when exercise was performed only at trough levels of the conventional drug. The decreases in exercise heart rate were correlated with plasma propranolol concentrations.