Left Ventricular Mechanics and Myocardial Blood Flow: Discussion

Left Ventricular Mechanics and Myocardial Blood Flow: DiscussionThe new findings of this study are as follows: (1) the restoration of a normal ventricular activation sequence after long-term right apical stimulation improves LV contractility and ventriculoarterial coupling in the short term but has no significant effect on diastolic function and MV02; and (2) the change from long-term asynchronous ventricular activation to synchronous ventricular activation leads to a significant increase in the flow in the dominant coronary artery, while reducing the flow reserve in the same artery.
LV Function and Ventriculoarterial Coupling
Previous studies have shown that right ventricular apical stimulation has a negative inotropic effect and also leads to disturbances of LV diastolic function. A study by Tantengco et al examined 24 young patients with normal segmental anatomy who received pacing from the right ventricular apex for a mean period of 9.5 years. They underwent noninva-sive assessment of global LV function with the fractional area of change derived from automated border detection echocardiography, coupled with Doppler indexes of myocardial performance. The patients demonstrated impaired regional and Doppler flow-derived indexes of LV systolic and diastolic function compared with control subjects. In shortterm studies, it has been shown that a change of pacing mode from DDD to AAI results in an improvement of LV contractility and mechanical energy efficiency. In patients receiving longterm pacing, however, apart from the functional changes that asynchronous ventricular activation entails, there are likely to be histologic disturbances and LV remodeling. other
In this study, we found that in such patients Ees, which is perhaps the most objective contractility index that is independent of LV loading, increased significantly a few minutes after a normal ventricular activation sequence was restored.

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