Abstract
Regulation of regional work is essential for efficient cardiac function. In patients with heart failure and electrical dysfunction such as left branch bundle block regional work is often depressed in the septum. Following cardiac resynchronisation therapy (CRT) this heterogeneous distribution of work can be rebalanced by altering the pattern of electrical activation. To investigate the changes in regional work in these patients and the mechanisms underpinning the improved function following CRT we have developed a personalised computational model. Simulations of electromechanical cardiac function in the model estimate the regional stress, strain and work pre- and post-CRT. These simulations predict that the increase in observed work performed by the septum following CRT is not due to an increase in the volume of myocardial tissue recruited during contraction but rather that the volume of recruited myocardium remains the same and the average peak work rate per unit volume increases. These increases in the peak average rate of work is is attributed to slower and more effective contraction in the septum, as opposed to a change in active tension. Model results predict that this improved septal work rate following CRT is a result of resistance to septal contraction provided by the LV free wall. This resistance results in septal shortening over a longer period which, in turn, allows the septum to contract while generating higher levels of active tension to produce a higher work rate.
Highlights
Cardiac resynchronization therapy (CRT) is an established treatment for patients with heart failure (HF) and dysnchrnous contraction usually manifested on the surface ECG as left branch bundle block (LBBB)
Previous studies have demonstrated that oxygen consumption, or analogously energy consumption, is indicative of the work performed by a muscle [8], [9]
There is a significant increase in the work rate performed by the septum upon CRT, a minor increase in the RV work rate and a slight decrease in the left ventricular (LV) work rate
Summary
Cardiac resynchronization therapy (CRT) is an established treatment for patients with heart failure (HF) and dysnchrnous contraction usually manifested on the surface ECG as left branch bundle block (LBBB). The observed changes following CRT are likely to be partially attributable to a redistribution of mechanical work across the heart [1] These changes in cardiac oxygen uptake occur immediately following CRT [10] as a result of an acute improvement in contractile timing. This suggests that part of the change in the distribution of energy consumption is a result of the post-operative changes in the distribution of mechanical work in the heart
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