Is there a clinically significant seasonal component to hospital admissions for atrial fibrillation?

Background

Atrial fibrillation is a common cardiac dysrhythmia, particularly in the elderly. Recent studies have indicated a statistically significant seasonal component to atrial fibrillation hospitalizations.

Methods

We conducted a retrospective population cohort study using time series analysis to evaluate seasonal patterns of atrial fibrillation hospitalizations for the province of Ontario for the years 1988 to 2001. Five different series methods were used to analyze the data, including spectral analysis, X11, R-Squared, autocorrelation function and monthly aggregation.

Results

This study found evidence of weak seasonality, most apparent at aggregate levels including both ages and sexes. There was dramatic increase in hospitalizations for atrial fibrillation over the years studied and an age dependent increase in rates per 100,000. Overall, the magnitude of seasonal difference between peak and trough months is in the order of 1.4 admissions per 100,000 population. The peaks for hospitalizations were predominantly in April, and the troughs in August.

Conclusions

Our study confirms statistical evidence of seasonality for atrial fibrillation hospitalizations. This effect is small in absolute terms and likely not significant for policy or etiological research purposes.     

Comparison of magnetic resonance imaging and ultrasonography in the evaluation of abdominal aortic aneurysms

Magnetic resonance imaging (MRI) was used to evaluate abdominal aortic aneurysms in 27 patients. The findings were compared retrospectively with CT, ultrasound (US), and angiography in 17 cases and prospectively with US in 10 cases. MRI identified the renal arteries in all cases, demonstrated involvement at or above the origin of the renal arteries in eight patients, and showed extension of the aneurysm into the iliac arteries in 12 cases. The outer dimension of the aneurysm, the diameter of the residual lumen, and the length of the aneurysm were measured easily from the MR images. The measurements of transverse dimension of the abdominal aortic aneurysm were similar for MRI, CT, and US. MRI more accurately defined extension above the renal arteries and below the aortic bifurcation. It is concluded that MRI provides the necessary information for the surveillance and preoperative evaluation of abdominal aortic aneurysms.     

Magnetic resonance imaging in the diagnosis and staging of renal and perirenal neoplasms

Thirty-one adult patients underwent magnetic resonance (MR) imaging after CT scans had demonstrated findings consistent with renal cell carcinoma. MR images were interpreted prospectively and independently of the CT findings. Because the CT scanning was performed at multiple institutions by many examiners, this study was not a direct comparison of CT versus MR. The preoperative diagnoses and staging of the neoplasms, as judged by MR, were compared with those obtained at laparotomy (n = 28), autopsy (n = 1), or biopsy (n = 2). Correct preoperative diagnoses were rendered in 31 patients (100%) on the basis of MR findings. The anatomic staging of 27 renal cell carcinomas was correctly performed by MR in 26 patients (86%). When compared with results of previous studies of the value of CT in the diagnosis and staging of renal neoplasms, MR appears to have several advantages in determination of the origin of the mass; the evaluation of vascular patency; the detection of perihilar lymph node metastases; and the evaluation of direct tumor invasion of adjacent organs. MR is sensitive in determining the extent of tumor thrombus and in evaluating invasion of the inferior vena caval wall. MR should assume an important role in the diagnosis and staging of renal neoplasms.     

Reciprocal up- and down-regulation of BDNF mRNA in tetanus toxin- induced epileptic focus and inhibitory surround in cerebral cortex

Chronic focal epilepsy is associated with synaptic plasticity and growth of new connections. Brain-derived neurotrophic factor (BDNF) is associated with each of these processes in normal brain and shows acute up-regulation in models of generalized epilepsy. Here, using an experimental model of focal epilepsy, we show persistent up-regulation of BDNF mRNA, independent of that of other growth factors, in association with the development and persistence of chronic seizures. In situ hybridization histochemistry revealed that rats perfused within 2-3 days after seizure onset had widespread increases in BDNF mRNA levels in the neocortex. Rats perfused at later times, however, showed focal up-regulation of BDNF mRNA at the injection site and down- regulation in a surrounding cortical zone. Nerve growth factor and neurotrophin-3 mRNAs were not significantly altered. These reciprocal changes in BDNF gene expression in the epileptic focus and the cortical surround may contribute to plastic changes in epileptic neuronal circuits that accompany the transition from acute to chronic epilepsy. BDNF down-regulation in the surround is likely to be associated with the inhibitory surround that hampers seizure spread, but facilitates the persistence of a chronic epileptic focus.