Heart Failure

The ventricles generate maximum efficiency when contracting simultaneously in systole.

If one ventricle 'leads' the other, it allows the septum to be displaced first to the contralateral side, and then back the other way during the later, second, period of ventricular systole. This is inter-ventricular dyssynchrony and is haemodynamically disadvantageous. The effect is considerably magnified in the context of pre-existing LV systolic impairment. A similar effect is seen if regions of the LV do not contract together, particularly if some contraction occurs after closure of the aortic valve. This 'wasted' contraction not only loses cardiac output into the aorta, but increases retrograde flow through the mitral valve into the LA and worsens mitral regurgitation. This is intra–ventricular dyssynchrony.

Theoretically both these problems can be overcome by artificially co-ordinating LV and RV contraction with each other, and with atrial contraction. Cardiac resynchronization devices can be combined in a single unit with an ICD, and are referred to as CRT-D(efib). Standard units are referred to as CRT-P(ace).