Thrombogenic potential of transcatheter aortic valve implantation with trivial paravalvular leakage

Abstract

Background: Significant paravalvular leakage after transcatheter aortic valve implantation (TAVI) correlates with increased morbidity and mortality, but adverse consequences of trivial paravalvular leakage have stimulated few investigations. Using a unique method distinctly different from other diagnostic approaches, we previously reported elevated backflow velocities of short duration (transients) in mechanical valve closure. In this study, similar transients were found in a transcatheter valve paravalvular leakage avatar.

Methods: Paravalvular leakage rate (zero to 58 mL/second) and aortic valve incompetence (volumetric back flow/forward flow; zero to 32%) were made adjustable using a mock transcatheter aortic valve device and tested in quasi-steady and pulsatile flow test systems. Projected dynamic valve area (PDVA) from the back illuminated mock transcatheter aortic valve device was measured and regional backflow velocities were derived by dividing volumetric flow rate by the PDVA over the open and closing valve phase and the total closed valve area derived from backflow leakage.

Results: Aortic incompetence from 1-32% generated negative backflow transients from 8 to 267 meters/second, a range not dissimilar to that measured in mechanical valves with zero paravalvular leakage. Optimal paravalvular leakage was identified; not too small generating high backflow transients, not too large considering volume overload and cardiac energy loss caused by defective valve behavior and fluid motion.

Conclusions: Thrombogenic potential of transcatheter aortic valves with trivial aortic incompetence and high magnitude regional backflow velocity transients was comparable to mechanical valves. This may have relevance to stroke rate, asymptomatic microembolic episodes and indications for anticoagulation therapy after transcatheter valve insertion.

Keywords: Transcatheter aortic valve implantation (TAVI); incompetence; leakage; paravalvular; transients.

Figure 1

Depiction of implanted Edwards Sapien XT TAVI with paravalvular leakage (PVL) through calcified irregular and tortuous pathways, indicated by arrows, resulting from tissue calcification (upper panel). The mock-TAVI (mTAVI) device is mounted within an adjustable PVL mechanism (lower panel). Differences in leaflet dynamics and geometry between the valves are assumed minor. The mTAVI device fabric was sealed with silicone rubber to reduce intravalvular leakage to ≈ –1.35 mL/s.

Figure 2

(A) Hydrodynamic and valve motion (PDVA) waveforms for mock-TAVI (mTAVI) device using Edwards-Perimount valve size 25 mm. Aortic valve incompetence (AI) range is trivial (1.0-5.2%). Cycles shown are those that gave the greatest backflow transients of the ten consecutive cycles acquired. Heart Rate 70/min; cardiac output 5 liters/minute; test fluid saline; mean systolic aortic pressure ≈100 mmHg; (B) AI range is mild (9.0-31.5%). See Figure 2A caption for other test conditions.

Figure 3

The mock-TAVI (mTAVI) device under various paravalvular conditions with aortic valve incompetence (AI) =1-32%. The ideal TAVI paravalvular condition (Star data point) is AI near ZERO. This negates large transients of regional backflow velocity (RBV_–max) where least thrombogenic potential is inferred. Black data points include trivial AI where intense transients generated by the closing valve infer high thrombogenic potential. White data points (AI>15%) have lower RBV_–max flow transients, however, transvalvular energy loss will increase during the closed valve interval with AI increase. The mean RBV_–max and range of variation for each experiment are shown (vertical bars, n=10 consecutive cycles). Suggested thrombogenic benchmark based on testing several bioprostheses with no paravalvular leakage (PVL) is shown for surgical aortic valve replacement (SAVR) reference. St Jude Medical (SJM) size 25 mm valve results is also shown for SAVR reference for a mechanical heart valve (MHV) with PVL = zero.

Figure S1

Valve motion waveform (PDVA) for mock-TAVI (mTAVI) device identifies initial moments when the device “opens” and “closes” (vertical timing lines). Volumetric flow rate waveform (lower-panel) shows compliance related confounding flows (dotted-line) and post experiment mitigation (solid-line). Replacement of the compliance “Included” data with compliance “Excluded” data is performed post experiment.

Figure S2

Additional waveforms of hydrodynamic and valve motion (PDVA) waveforms for a St Jude Medical (SJM), an Edwards-Perimount pericardial valve, and the mock-TAVI (mTAVI) device for comparative regional backflow velocity (RBV) perspective. See Figure 2A caption for other test conditions.

Figure S3

Apparatus for calibration of the leakage orifice (geometric leakage area versus volumetric leakage rate) and for measuring closed mock-TAVI (mTAVI) device volumetric leakage rate preset for various paravalvular leakages (PVL). Knowing mTAVI device leakage rate, total residual backflow area can be determined by means of the leakage orifice calibration. The mTAVI device is evaluated for leakage prior to pulsatile flow testing.

Figure S4

Diagram of leakage orifice (top panel) and calibrations for fluids with different viscosity (saline and glycerin-saline). The six sets of holes were sequentially blocked thus obtaining six data pairs for each calibration line. For very small leakage pathways, the primary determinant of leak flow rate is the total geometric leakage flow area.