Seasonal variation in occurrence of aortic diseases: summer low or winter high?

Background & Objectives In analogy with other cardiovascular events, e.g., myocardial infarction and stroke, acute aortic diseases do not randomly occur over time but show definite chronobiologic variations characterized by a higher frequency during morning hours and winter months . The aim of this study, based on the large number of cases of the database of the Emilia-Romagna region of Italy, was to confirm the existence of a seasonal variation in acute aortic diseases. Subjects & Methods We considered all cases of hospital admissions recorded at the database of the Emilia-Romagna region of Italy (years 2000–2006), with the following ICD-9-CM codes: 441, aortic aneurysm and dissection; 441.0, dissection of the aorta; 441.00, unspecified site; 441.01, thoracic; 441.02, abdominal; 441.03, thoracoabdominal; 441.1, thoracic aneurysm, ruptured; 441.3, abdominal aneurysm, ruptured; 441.5, aortic aneurysm of unspecified site; 441.6, thoracoabdominal aneurysm, ruptured. Cases were categorized by month of hospitalization, and c2 goodness of fit was used for statistical analysis for total population and subgroups by gender, age, and type of acute event, e.g., dissection or rupture. Results The total population consisted of 4,615 cases (77% males, mean age 70±13 years, 59.8% dissections, 40.2% ruptures). A seasonal pattern, characterized by a lowest frequency in summer (Figure 2), was shown for total cases (p < 0.0001), males (p < 0.0001), females (p = 0.017), Age subgroups: (< 60 years: p < 0.0001; 61-74 years: p < 0.01;> 75 years: p = 0.049), and dissection (p<0.0001), but not for rupture. Discussion Previous studies showed an increased frequency of onset of aortic diseases in winter. We found a significant summer low rather than a winter high. It is likely that summer might have a protective effect against those factors related to cold exposure, e.g., increased blood pressure (BP), arterial spasm, blood viscosity, lipid levels, clotting activity. Summer has been associated with the lowest and winter with the highest clinic BP in both normotensive and hypertensive subjects, independent of therapy. The different patterns between dissection and rupture might reflect pathophysiologic differences between the two clinical entities, where the increase in sympathetic activity and BP plays a major role especially for dissection.