The ―Merry Christmas Coronary‖ and ―Happy New Year Heart Attack‖ phenomenon. Circulation 2004

In 1999, my research group published a study that exam-ined whether there are seasonable variations in cardiacmortality in a location where winter weather is mild— Los Angeles County, Calif.1 During a 12-year period, there were consistently more deaths from ischemic heart disease during the winter than there were during the summer. About one third more deaths from ischemic heart disease were recorded in December and January than from June through September in Los Angeles County. We initially thought that this phenomenon might be explained by colder temperatures. Colder temperatures have been associated with an increase in vascular resistance, coronary vasospasm, blood pressure, and hemostasis, as reviewed by Spencer et al.2 Temperatures in Los Angeles during the winter, although colder than they are during the summer, are still mild as compared with other climates. When we plotted daily rates of death from ischemic heart disease in Los Angeles County during November