The American journal of cardiology
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The duration of the QT interval on the surface electrocardiogram represents the time required for all ventricular depolarization and repolarization processes to occur. Among the many physiologic and pathologic factors that contribute to the QT interval, heart rate plays a major role. Several approaches have been used to correct the QT interval, all of which take into account the heart rate at which the interval is measured. ⋯ Any correction formula is likely to introduce an error in assessing the QTc interval. Although the importance of this error should not be minimized, the corrected QT interval remains useful in assessing the effects of drugs on the duration of repolarization. For this purpose, Fridericia's cube-root formula is preferable to Bazett's square-root formula.(ABSTRACT TRUNCATED AT 250 WORDS)
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Patients admitted to the coronary care unit who received both intravenous nitroglycerin and heparin were studied to evaluate heparin dosage requirements. Physicians ordered all nitroglycerin and heparin doses as well as coagulation studies without knowledge of this study. Activated partial thromboplastin time (APTT) values obtained during steady-state heparin administration were considered therapeutic if the ratio of APTT/APTT-baseline was > or = 1.5. ⋯ Similarly, analysis of variance revealed a significant difference in the initial therapeutic dose (p < 0.05), but not the initial therapeutic dose standardized to weight among 5 different nitroglycerin dosage ranges (10 to 533 micrograms/min). Neither aspirin use, thrombolytic therapy nor decreasing or discontinuing the nitroglycerin dose significantly affected heparin requirements. Thus, contrary to prior reports, clinically significant heparin resistance induced by nitroglycerin was not found.
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Randomized Controlled Trial Multicenter Study Comparative Study Clinical Trial
Randomized antiarrhythmic drug therapy in survivors of cardiac arrest (the CASCADE Study). The CASCADE Investigators.
The Cardiac Arrest in Seattle: Conventional Versus Amiodarone Drug Evaluation (CASCADE) study evaluated antiarrhythmic drug treatment of survivors of out-of-hospital ventricular fibrillation (VF) not associated with a Q-wave myocardial infarction who were at especially high risk of recurrence of VF. Therapy was randomized to empiric treatment with amiodarone versus treatment with other antiarrhythmic drugs guided by electrophysiologic testing, Holter recording, or both (conventional therapy). The primary end points of the study were cardiac mortality, resuscitated cardiac arrest due to documented VF, or complete syncope followed by a shock from an implanted automatic defibrillator. ⋯ Mean left ventricular ejection fraction was 0.35, and 102 patients (45%) had a prior history of congestive heart failure. Survival free of cardiac death, resuscitated VF, or syncopal defibrillator shock for the entire population was 75% at 2 years (amiodarone, 82%; conventional, 69%), 59% at 4 years (amiodarone, 66%; conventional, 52%), and 46% at 6 years (amiodarone, 53%; conventional, 40%); p = 0.007. The survival free of cardiac death and sustained ventricular arrhythmias was 65% at 2 years (amiodarone, 78%; conventional, 52%), 43% at 4 years (amiodarone, 52%; conventional, 36%), and 30% at 6 years (amiodarone, 41%; conventional, 20%); p < 0.001.