Effects of biventricular pacing on left heart twist and strain in a porcine model of right heart failure.

BACKGROUND: Biventricular pacing (BiVP) improves cardiac output (CO) in selected cardiac surgery patients, but response remains variable, necessitating a better understanding of the mechanism. Accordingly, we used speckle tracking echocardiography (STE) to analyze BiVP during acute right ventricular pressure overload (RVPO). MATERIALS AND METHODS: In nine pigs, the inferior vena cava (IVC) was snared to decrease CO and establish a control model. Heart block was induced, the pulmonary artery snared, and BiVP initiated. Echocardiograms of the left ventricular midpapillary level were taken at varying atrioventricular delay (AVD) and interventricular delay (VVD) for STE analysis of regional circumferential strain (CS) and radial strain (RS). Echocardiograms were taken of the left ventricular base, midpapillary, and apex during baseline, IVC occlusion, and each BiVP setting for STE analysis of twist, apical and basal rotations, CS, RS, and synchrony. Indices were correlated against CO with mixed linear models. RESULTS: During IVC occlusion, CO correlated with twist, apical rotation, RS, RS synchrony, and CS (P < 0.05). During RVPO with BiVP, CO only correlated with RS synchrony and CS (P < 0.05). During AVD and VVD variations, CO was associated with free wall RS (P < 0.008). CO correlated with septal wall CS during AVD variation and free wall CS during VVD variation (P < 0.008). CONCLUSIONS: In an open chest model, twist, RS, RS synchrony, and CS analyzed by STE may be noninvasive surrogates for changes in CO. During RVPO, changes in RS synchrony and CS with varying regional strain contributions may be the primary mechanism in which BiVP improves CO. Lack of correlation of remaining indices may reflect postsystolic function.

Effect of Left Versus Right Radial Artery Approach for Coronary Angiography on Radiation Parameters in Patients With Predictors of Transradial Access Failure.

Left transradial approach (TRA) for coronary angiography is associated with lower radiation parameters than right TRA in an all-comers population. The aim of this study was to determine the effects of left versus right TRA on radiation parameters in patients with predictors of TRA failure. Patients with predictors of TRA failure (≥3 of 4 following criteria: age ≥70 years, female gender, height ≤64 inches, and hypertension) referred to TRA operators were randomized to either right (n = 50) or left (n = 50) TRA, whereas those referred to transfemoral approach (TFA) operators were enrolled in a prospective registry (n = 50). The primary end point was the radiation measure of dose-area product (DAP). In an intention-to-treat analysis, DAP (34.1 Gy·cm(2) [24.9 to 45.6] vs 41.9 Gy·cm(2) [27.3 to 58.0], p = 0.08), fluoroscopy time (3.7 minutes [2.4 to 6.3] vs 5.6 minutes [3.1 to 8.7], p = 0.07), and operator radiation exposure (516 µR [275 to 967] vs 730 µR [503 to 1,165], p = 0.06) were not significantly different between left and right TRA, but total dose (411 mGy [310 to 592] vs 537 mGy [368 to 780], p = 0.03) was significantly lower with left versus right TRA. Radiation parameters were lowest in the TFA cohort (DAP 24.5 Gy·cm(2) [15.7 to 33.2], p <0.001; fluoroscopy time 2.3 minutes [1.5 to 3.7], p <0.001; operator radiation exposure 387 µR [264 to 557]; total dose 345 mGy [250 to 468], p = 0.001). Results were similar after adjustment for differences in baseline characteristics. In conclusion, median measurements of radiation were overall not significantly different between left versus right TRA in this select population of patients with predictors of TRA failure. All measurements of radiation were lowest in the TFA group.

Short-term reduction in intrinsic heart rate during biventricular pacing after cardiac surgery: a substudy of a randomized clinical trial.

BACKGROUND: The Biventricular Pacing After Cardiac Surgery trial investigates hemodynamics of temporary pacing in selected patients at risk of left ventricular dysfunction. This trial demonstrates improved hemodynamics during optimized biventricular pacing compared with atrial pacing at the same heart rate 1 and 2 hours after bypass and reduced vasoactive-inotropic score over the first 4 hours after bypass. However, this advantage of biventricular versus atrial pacing disappears 12 to 24 hours later. We hypothesized that changes in intrinsic heart rate can explain variable effects of atrial pacing in this setting. METHODS: Heart rate, mean arterial pressure, cardiac output, and medications depressing heart rate were analyzed in patients randomized to continuous biventricular pacing (n = 16) or standard of care (n = 18). RESULTS: During 30-second testing periods without pacing, intrinsic heart rate was lower in the paced group 12 to 24 hours after bypass (76.5 ± 17.5 vs 91.7 ± 13.0 beats per minute; P = .040) but not 1 or 2 hours after bypass. Cardiac output (4.4 ± 1.2 vs 3.6 ± 1.9 L/min; P = .054) and stroke volume (53 ± 2 vs 42 ± 2 mL; P = .051) increased overnight in the paced group. Vasoactive medication doses were not different between groups, whereas dexmedetomidine administration was prolonged over postoperative hours 12 to 24 in the paced group (793 ± 528 vs 478 ± 295 minutes; P = .013). CONCLUSIONS: These observations suggest that hemodynamic benefits of biventricular pacing 12 to 24 hours after cardiopulmonary bypass lead to withdrawal of sympathetic drive and decreased intrinsic heart rate. Depression of intrinsic rate increases the apparent benefit of atrial pacing in the chronically paced group but not in the control group. Additional study is needed to define clinical benefits of these effects.