Stimulation of cardiac sympathetic nerves for LV inotropy

Stimulation of cardiac sympathetic nerves for improving the left ventricular inotropy is a novel concept which has been tried out in a recent study published in Circulation [Meyer C et al. Augmentation of Left Ventricular Contractility by Cardiac Sympathetic Neural Stimulation. Circulation. 2010;121:1286-1294.] What they aimed at was selective stimulation of the sympathetic nerves innervating the left ventricle, avoiding general sympathetic stimulation which would cause sinus tachycardia and increase in the peripheral vascular resistance which would be deleterious.
It was a study conducted in 20 sheep with high frequency (200 Hz) stimulation during the myocardial refractory period. The electrodes were placed inside the coronary sinus in order to stimulate the left ventricular sympathetic nerves. The stimulation produced significant increase in left ventricular systolic pressure and the rate of development of systolic pressure without changes in sinus rate or PR interval. The rate of diastolic relaxation also improved. There was no change in systemic vascular resistance and right ventricular pressure. There was increase in the circumferential and radial strain in all left ventricular segments by ultrasound evaluation. The effects were blocked by beta one receptor blockade. Histological evaluation of the stimulation site revealed adrenergic nerve bundles.
A clinical summary associated with this article suggests that this approach may be used in the management of heart failure in future. As a corollary, catheter ablation of left ventricular sympathetic nerves around the coronary sinus may be used in patients with severe ventricular arrhythmias (electrical storm) as a last resort.