Increased risk of congestive heart failure among infarctions with nighttime onset

Background The onset of acute myocordial infarction varies by time of day, with a peak in the morning and a trough at night. Whether infarct-related c omplications differ by the timing of the infarction is unknown. Methods and Results In the Determinants of Myocardial Infarction Onset stud y, we performed chart reviews and Face-to-face interviews with 3625 patient s with acute myocardial infarction. We assessed the time of onset of sympto ms, the presence of ventricular tachycardia or congestive heart failure, an d peak creatine kinase levels (in 1043 patients). We Found significant circ adian variation in the risk of congestive heart failure (P = .001). The ris k dropped from 17% for infarctions that began between 6 PM and midnight to 10% for infarctions that began between 6 AM and noon. Adjustment for differ ences in the time from symptom onset to presentation for care and use of th rombolytic agents did not change the results, We found no circadian variati on in the risk of ventricular tachycardia or in peak creatine kinase levels . Conclusions The risk of congestive heart failure is highest among infarctio ns that begin at night. Further research may clarify whether this reflects differences in the pathophysiologic characteristics of infarction or the qu ality of medical care provided for daytime and nighttime infarctions.