The Effect of Intravenous Amiodarone on Heart Rate in Patients with Acute Myocardial Infarction or Ischemia and Sinus Tachycardia

Sinus tachycardia in the setting of acute myocardial infarction or ischemia may worsen the ischemic injury. Intravenous (IV) amiodarone is an effective antiarrhythmic agent for a variety of supraventricular and ventricular arrhythmias. In addition, a beneficial anti-ischemic effect has also been demonstrated in experimental and human studies. The effect of IV amiodarone on heart rate is controversial and difficult to interpret because of possible increased sympathetic tone caused by vasodilation. Studies have shown either no significant change or a reduction in heart rate following its administration. However, most of the patients studied have had heart rates within the normal range. We investigated the efficacy of IV amiodarone in slowing the heart rate in a group of patients with acute myocardial infarction or ischemia and sinus tachycardia.

Material and Methods
Patients admitted to our coronary care unit with acute myocardial ischemia or infarction who presented with or developed sinus tachycardia (sinus rates >95 beats/min) during the first 36 hours of admission were considered for amiodarone administration.
Patients presenting with known causes of sinus tachycardia such as anemia or hyperthyroidism were excluded. Those with sinus tachycardia and fever or congestive heart failure were initially excluded. However, if sinus tachycardia persisted for at least two hours after the correction of the above-mentioned causes, they were included in the study. Patients in whom sinus tachycardia was thought to be related to the administration of IV isosorbide dinitrate or other drugs with positive chronotropism were excluded.
The definition of acute myocardial infarction was based on the triad of typical prolonged chest pain, evolutionary ST-T changes with or without development of pathologic Q waves, and typical enzymatic curve. Acute myocardial ischemia was defined as typical chest pain with ST-T wave changes but without pathologic cardiac enzymes. Inferior myocardial infarction or ischemia was diagnosed when the inferior ECG leads were involved, whereas anterior infarction or ischemia were diagnosed when the ECG changes included the precordial leads. The hemodynamic status of each patient was determined according to the Killip classification. A Swan-Ganz catheter was inserted only when clinically indicated.

Category: Myocardial Infarction

Tags: heart rate, Ischemia, myocardial infarction, sinus tachycardia