Why inotropes continue to disappoint in heart failure

Impact of Different Pacing Modes on Left Ventricular Contractility Following Cardiopulmonary Bypass

BACKGROUND

Acute left ventricular (LV) dysfunction after cardiopulmonary bypass (CBP) is a serious complication in cardiac surgery. The aim of this study was to investigate the effect of different epicardial pacing modes on LV contractility and changes of myocardial oxygen extraction (MVO(2)) following CPB in an animal model. The utility of conductance catheter measurement versus left ventricular outflow tract mean systolic acceleration (LVOT(Acc)) for quantification of LV function was evaluated.

METHODS

Fourteen piglets underwent median sternotomy and CPB for 90 minutes, myocardial ischemia for 60 minutes, and reperfusion for 30 minutes. Different pacing modes were obtained before and after CPB to investigate changes in LV function. LV Function was quantified by end-systolic-pressure-volume relationships (ESPVR) as measured by the conductance catheter method and by LVOT(Acc) obtained from transepicardial echocardiographic studies.

RESULTS

LV contractility improved significantly by biventricular and atrial pacing compared with natural sinus rhythm (SR). MVO(2) remained stable or even decreased with biventricular pacing after surgery compared with SR. Right ventricular pacing resulted in poor LV-function with a rise of MVO(2). LVOT(Acc) showed a strong correlation to invasively measured ESPVR.

CONCLUSION

Postoperative biventricular pacing was associated with an improved LV contractility without rise of MVO(2) compared with SR and atrial pacing. At termination of CPB, this appears to facilitate the management of LV failure and potentially may reduce the need for inotropic support, additionally protecting myocardial metabolism. The echocardiographic assessment of LVOT(Acc) was a simple and reliable as well as effective method to quantify LV contractility and showed a good correlation with the more invasive conductance catheter.

Left ventricular or biventricular pacing improves cardiac function at diminished energy cost in patients with dilated cardiomyopathy and left bundle-branch block

BACKGROUND

Left ventricular or biventricular pacing/stimulation can acutely improve systolic function in patients with dilated cardiomyopathy (DCM) and intraventricular conduction delay by resynchronizing contraction. Most heart failure therapies directly enhancing systolic function do so while concomitantly increasing myocardial oxygen consumption (MVO(2)). We hypothesized that pacing/stimulation, in contrast, incurs systolic benefits without raising energy demand.

METHODS AND RESULTS

Ten DCM patients with left bundle-branch block (ejection fraction 20+/-3%, QRS duration 179+/-3 ms, mean+/-SEM) underwent cardiac catheterization to measure ventricular and aortic pressure, coronary blood flow, arterial-coronary sinus oxygen difference (DeltaAVO(2)), and MVO(2). Data were measured under sinus rhythm or with left ventricular or biventricular pacing/stimulation at the same heart rate. These results were then contrasted to intravenous dobutamine (n=7) titrated to match systolic changes during LV pacing. Systolic function rose quickly and substantially from LV pacing (18+/-4% rise in arterial pulse pressure, which correlates with cardiac output, and 43+/-6% increase in dP/dt(max); both P<0.01). However, DeltaAVO(2) and MVO(2) declined -4+/-2% and -8+/-6.5%, respectively (both P<0.05). Similar results were obtained with biventricular activation. In contrast, dobutamine raised dP/dt(max) 37+/-6%, accompanied by a 22+/-11% rise in per-beat MVO(2) (P<0.05 versus pacing).

CONCLUSIONS

Ventricular resynchronization by left ventricular or biventricular pacing/stimulation in DCM patients with left bundle-branch block acutely enhances systolic function while modestly lowering energy cost. This should prove valuable for treating DCM patients with basal dyssynchrony.