Rapid ventricular pacing during TAVI frequently induces arrest and delayed recovery of microvascular perfusion

Background: Rapid Ventricular Pacing (RVP) is an established technique for temporary arrest of LV ejection during Transcatheter Aortic Valve replacement (TAVI). As microvascular Perfusion (MicrPF) is crucial for adequate tissue oxygenation and potentially linked to outcome, the purpose of this study was to investigate alterations of MicrPF associated with RVP during TAVI. Methods: We studied 29 patients (pts., mean age 81.8±6.9years, n=18 female. Euroscore 33±12%) undergoing RVP during TAVI. MicrPF was analysed using Sidestream-Darkfield (SDF) imaging, which was performed by video recordings of the sublingual microvasculature. SDF-imaging was started 8sec before and continued until 12sec after RVP. The microvascular flow index (MFI), a semi-quantitative scale quantifying the microflow (0: no flow = no flow present for the entire duration of the clip; 1: intermittent flow = flow present 50% but <100% of the duration of the clip or very slow flow for the entire duration of the clip; and 3: continuous flow = flow present for the entire duration of the clip) was determined repeatedly every 2sec in each video sequence. MFI-calculation was performed by averaging flow in the four quadrants of the video images for small (10-25μm) and medium (26-50μm) sized vessels each by a blinded investigator. Results: After a mean RVP-duration of 14sec (range 6-29), mean arterial pressure (MAP) dropped from 69±14mmHg to 40±7mmHg (p<0.001). This was associated with a significant decrease of mean MFI in small and medium vessels from 2.21±0.65 and 2.35±0.53 to 0.91±0.66 (p<0.001) and 1.09±0.76 (p<0.001), respectively. MFI decreased by 0.108 every two seconds, "no flow" (MFI<1) was oberved in 12pts (41.4%) after a variable RVP-duration. After termination of RVP, MAP rapidly recovered to baseline values (66±12mmHg, p=0.34 vs. baseline). However mean MFI remained significantly below baseline values (small: 1.72±0.81, p=0.001 vs. baseline; medium: 1.86±0.86; p=0.005 vs. baseline) within the next 12 seconds of measurement. Conclusions: RVP during TAVI is associated with a continuous decrease of microflow. Arrest of mircovascular perfusion ("no flow") occurs in a significant proportion of patients and becomes more likely with prolonged RVP. After termination of RVP there is a delayed recovery of microflow despite already normalized MAP.