Eastern Cardiothoracic Surgical Society

Preventing Knot Failure in Mitral Valve Chordal Replacement Using ePTFE
Jacob R. Miller, Corey R. Deeken, Shuddhadeb Ray, Matthew C. Henn, Timothy S. Lancaster, Richard B. Schuessler, Ralph J. Damiano, Spencer J. Melby. Washington University in St. Louis, St. Louis, MO USA.

Objective: Expanded polytetrafluoroethylene (ePTFE) suture is commonly used for chordal replacement in mitral valve repair, but due to material characteristics, knots can unravel. Our aim was to determine the knot security, including how many throws are necessary to prevent knot failure, with two currently available ePTFE suture types.

Methods: Knots were evaluated for the maximum load prior to knot failure based on the number of throws (6, 8,10 and 12), tension to secure each throw (10, 50 and 85% of the knot holding power) and type of ePTFE (2 suture types). Ten knots per group were analyzed. A relative physiological force of 2N was used for comparison.

Results: A total of 240 knots were evaluated. For all knots, the mean load to knot failure was 11.1 5.8N. Failure occurred due to unraveling in 141 (59%) at 7.1 4.1N and breaking in 99 (41%) at 16.7 2.0N (p<0.01). Increasing throws increased the maximum load to failure (p<0.01), with a significant increase between 8 (8.2 3.9N) and 10 throws (15.3 3.4N) (p<0.01, Figure SA6-1) due to the reduced rate of unraveling. Six (5%) of each suture type unraveled at 2N, all occurring with less than 10 throws (Table SA6-1).

Conclusions: ePTFE suture, used commonly for mitral valve chordal replacement, has adequate strength to prevent breakage. However, there exists a risk of knot unraveling. This study demonstrated that, at physiologic conditions, the unravelling of knots is significantly reduced by performing at least 10 throws with ePTFE suture.

Figure 1 –

Maximal Load Prior to Knot Failure Based on Number of Throws, Grouped by Method of Failure