SUMMARYThere have only been a few studies of the chronobiological occurrence of acute aortic dissection (AAD), and most were international and multicentered. The aim of the present study, conducted at only one center, was to determine the most frequent daily, monthly, and seasonal occurrences of AAD.The study population included 204 patients (66.5% male) treated at our institute between January 1, 1998 and January 1, 2004. A significantly higher frequency of AAD occurred from 6:00 AM to 12:00 noon, compared with other time periods (P < 0.001). The results showed a significant circadian variation in AAD (P < 0.001) with a peak between 9:00 AM and 10:00 AM. No significant variation was found for the day of the week; however, AAD occurred most frequently on Wednesday and Monday. The frequency of AAD was found to be significantly higher during winter versus other seasons (P < 0.001). The analysis of monthly variations of the onset of AAD confirmed a peak in February (12.9%) and in January (12.3%).Similar to other cardiovascular diseases, AAD exhibits significant circadian and seasonal/monthly variations. Our findings indicate that the prevention of AAD, especially during the aforementioned vulnerable periods, is possible by adequate tailoring of the treatment of hypertension, which is the main AAD predisposing factor. (Int Heart J 2006; 47: 585-595)

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The definition of a favorable CRT response influenced the optimal predictor variable(s). Standardization of defining a favorable response to CRT is needed to guide clinical decision making processes.