Morning increase in the time of onset of sustained ventricular tachycardia

A morning increase in the occurrence of cardiac events has recently been described in patients with coronary artery disease who present with acute myocardial infarction, sudden cardiac death and unstable angina.¹ Almost all of these reports have demonstrated that these events are more likely to occur between 6 a.m. and noon than during other times of the day. Several mechanisms have been postulated to explain this phenomenon, including increased platelet aggregation,² elevated plasma catecholamines,³ increased coronary artery tone⁴ or other factors either acting alone or in combination. Patients with sustained ventricular tachycardia (VT) frequently have advanced structural heart disease, most often related to underlying coronary artery disease. Data from ambulatory electrocardiographic recordings of patients who have an out-of-hospital cardiac arrest without acute myocardial infarction show that the most common initial arrhythmia is monomorphic VT, which is frequently preceded by a period of acceleration of the sinus rate.⁵ Therefore, we investigated if the time of onset of VT might show a similar pattern.