The impact of atrial dilatation on conduction heterogeneity at bachmann's bundle

Atrial fibrillation (AF) occurs more frequently in patients with atrial dilatation. Especially conduction disorders at Bachmann’s bundle (BB) are thought to contribute to the development of AF. BB is a muscular bundle and the main route of conduction between the left atrium and the right atrium. Since the fibers of BB are not wrapped in a layer of fibrous tissue, volume overload in the left or right atrium can increase stretch on BB, potentially disrupting these fibers. However, the effect of atrial dilatation on the presence and severity of conduction disorders at BB is still unknown.

To determine the effect of atrial dilatation on conduction heterogeneity at BB during sinus rhythm.

High-resolution epicardial mapping (192 electrodes; interelectrode distance 2 mm) at BB was performed in 132 patients without a history of AF undergoing elective open heart surgery. Inter-electrode conduction times (CTs) were used to construct the relative frequency distribution histograms and analyze the 5th percentile and maximum CT. Conduction delay (CD) was defined as CT differences of 7 to 11 ms and conduction block (CB) as CT≥12 ms. The amount, number and maximum length of lines of CD, CB and CDCB were analyzed. Signal morphology was analyzed, with fractionation being classified into 4 categories: singles (one deflection), short doubles (two deflections with a distance <15 ms), long doubles (two deflections with a distance ≥15 ms) and complex (≥ 3 deflections). The left atrial volume index (LAVI) and right atrial volume index (RAVI) of all patients were determined from preoperative echocardiographic recordings using the body surface area (BSA) and the Biplane Area-Length Method for LAVI and the Single Plane Area-Length method for RAVI. All data were analyzed in a linear regression. Skewed data were modified into a normal distribution using a log-transformation.

Conduction parameters, unipolar voltages and fractionation at BB were not significantly associated with the LAVI (p≥0.05). For the right atrium, an increasing RAVI was significantly associated with less single potentials (β = -0.216; p = 0.025) and more short double potentials (β = 0.201; p = 0.034). Other potential morphology parameters (long double-, complex fractionated potentials), as well as conduction parameters and unipolar voltages did not show a significant association with the RAVI (p≥0.05).

There was a limited effect of right atrial dilatation on the amount of conduction disorders at BB and no effect of left atrial dilatation any of the conduction parameters. These findings imply that atrial dilatation has no direct effect on conduction at BB.