Angiographic anatomy of the inferior right atrial isthmus in patients with and without history of common atrial flutter.

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Abstract
Background —Although most ablative procedures undertaken for common atrial flutter target the inferior right atrial isthmus, comparative studies of the morphology of this area are lacking. Our study examines its angiographic anatomy, making correlations with postmortem specimens, to provide a better understanding of the anatomic substrate of this arrhythmia. Methods and Results —The gross morphological features and dimensions of the area between the orifice of the inferior caval vein and the attachment of the septal leaflet of the tricuspid valve were determined from angiograms made in 23 patients with documented atrial flutter and 30 control subjects. For comparison, we studied 20 normal heart specimens. When viewed in right anterior oblique projection, 2 morphologically distinct areas were identified. In the specimens, the inferior isthmus measured a mean length of 30±4 mm, not significantly different from the dimensions obtained from angiograms of control subjects. The mean length of the isthmus, however, was greater in patients with common atrial flutter than those without (37±8 versus 28±6 mm). Patients with atrial flutter and structural heart disease had an even longer isthmus than those with flutter alone (39.6±8 versus 33±7 mm). Compared with those without flutter, the atrial diameter was also larger in patients with flutter (57.6±9 versus 48.5±6 mm). Reevaluation carried out at follow-up 10±2 months after ablation did not show any reduction in atrial size, although contractility improved. Conclusions —The inferior isthmus and right atrium in patients with common atrial flutter were significantly larger than those in a control population.

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