006 Improvement in coronary blood flow with acute biventricular pacing is predominantly due to an increase in a diastolic backward-travelling decompression (suction) wave (2012)

Background Normal coronary blood flow is principally determined by a backward-travelling decompression (suction) wave in diastole. This wave may be attenuated in chronic heart failure, reducing blood flow, as regional relaxation and contraction overlap in timing. We hypothesised that biventricular pacing by restoring left ventricular (LV) synchronisation and improving LV relaxation might increase this decompression wave, improving coronary flow. Method and Results Ten CHF patients (9 males; age 65±12; EF 26±7%) with left bundle branch block (LBBB, QRS duration 174±18 ms) were atrio-biventricularly paced at 100 bpm. LV pressure was measured and wave intensity calculated from invasive coronary flow velocity and pressure, with native conduction (LBBB) and during biventricular pacing at atrioventricular (AV) delays of 40 ms (BiV-40), 120 ms (BiV-120), and separately pre-identified haemodynamically-optimal AV delay (BiV-Opt). Compared against LBBB, BiV-Opt enhanced coronary flow by 15±4% (p=0.003), LV dP/dt max by 19±4% (p&lt;0.001) and negdP/dt max by 16±3% (p&lt;0.001). The cumulative intensity of the diastolic backward decompression (suction) wave increased by 36±8% (p=0.011). The majority of the increase in coronary flow occurred in diastole (64±8%, p=0.03). The systolic compression waves also increased, forward by 33±11% (p=0.043) and backward by 33±10% (p=0.014). BiV-120 generated a smaller LV dP/dt max (by 23±12%, p=0.034) and negdP/dt max (by 23±10%, p=0.039) increase than BiV-OPT, against LBBB as reference; BiV-Opt and BiV-120 were not statistically different in coronary flow or waves. BiV-40 was no different from LBBB. Conclusions When biventricular pacing improves left ventricular contractility, it increases coronary blood flow, predominantly by increasing the dominant diastolic backward decompression (suction) wave. Abstract 006 Table 1 Cumulative wave intensity of major left coronary artery waves and comparison of these between all four pacing states. Data are presented as mean±SEM Wave Intensity (AUC) ×10 3 W/m 2 /s LBBB Biv-40 BiV-120 BiV-OPt p Value (BiV-Opt vs LBBB) p Value (Biv-40 vs LBBB) Systole 1. Forward compression 9.1±1.9 8.6±1.9 11.4±2.3 12.1±2.5 0.04 0.51 2. Backward compression 7.5±1.5 7.2±1.7 9.0±1.6 9.9±1.9 0.01 0.75 Net wave contribution to forward flow (1 minus 2) 1.6±1.4 1.4±1.0 2.4±1.3 2.3±1.7 Diastole 3. Forward decompression 2.1±0.5 3.2±0.7 3.5±0.8 3.3±0.6 0.15 0.20 4. Late forward compression (suction) 3.2±0.8 2.4±0.9 2.7±0.6 2.8±0.9 0.76 0.42 5. Backward decompression (suction) 7.8±1.4 7.6±1.3 10.1±2.0 10.4±2.1 0.01 0.71 Net wave contribution to forward flow (5 plus 4 minus 3) 8.8±1.9 6.7±1.8 9.3±2.4 9.9±2.1 p Value Proportion of diastolic contribution to total net wave contribution to forward flow 85±5% 83±4% 80±6% 81±5% 0.62 Abstract 006 Figure 1 Impact of LV dp/dt max and LV neg dp/dt max on their temporally corresponding coronary waves. In each part of the cardiac cycle, the peak rate of intraventricular pressure change (LV dp/dt max for systole, and LV negdP/dt max for diastole) correlated with the corresponding waves, consistent with myocardial compression and decompression of the coronary microcirculation generating the waves.