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Is the presence of interatrial septal hypertrophy a marker for atrial fibrillation in the elderly?

Interatrial septal thickness (IST) appears to increase with heart weight, body surface area, and the presence of vacuolated fat cells within the atrial septum. The increased thickness of the atrial septum is an infrequently observed but readily recognized entity by echocardiography. Several reports have suggested that some cardiac arrhythmias, particularly those of atrial origin, may be a consequence of this fatty deposition. However, to date, no study has correlated the presence of atrial fibrillation with IST in the elderly. This is of particular importance as this rhythm is so prevalent in this population. Accordingly, a retrospective analysis was conducted in a group of 40 patients, age 65 and older, to measure IST using transthoracic echocardiography. Furthermore, measurements of right and left atrial size, body surface area, left ventricular wall thickness, and left ventricular ejection fraction were recorded. Group I consisted of 20 patients with known atrial fibrillation (eight males and 12 females; mean age 78+/-8 years) and group II consisted of 20 patients in normal sinus rhythm (three males and 17 females; mean age 74+/-6 years). There was no difference between the two groups in terms of body surface area (1.83 vs. 1.79 m2; p<0.78); left ventricular wall thickness (1.16 vs. 1.12 cm; p<0.58); and left ventricular ejection fraction (48% vs. 55%; p<0.17). Group I had somewhat larger right atrial (4.2 vs. 3.4 cm; p<0.001) and left atrial (4.7 vs. 4.1 cm; p<0.02) dimensions than group II. Furthermore, IST was found to be the most significant variable that differentiated patients with atrial fibrillation from patients with normal sinus rhythm (1.39 vs. 0.85 cm; p<0.0001). Even after adjusting for all the covariables, IST remained statistically significant (p<0.0001). The findings of this pilot study show a strong correlation between IST and atrial fibrillation. Although the stimulus for the increased thickness of the atrial septum remains elusive, IST may identify a structural cause for atrial fibrillation in elderly patients that is easily identified by transthoracic echocardiography.