Volume overload modulates effects of cardiac resynchronization therapy independently of myocardial reperfusion: results of the RESYNC study

Regional and global strain changes during biventricular pacing in a porcine model of acute left ventricular volume overload

OBJECTIVES

Biventricular pacing may ameliorate symptoms of acute heart failure. Speckle-tracking echocardiography can assess cardiac function to elucidate mechanisms of benefit. Accordingly, radial and circumferential strain and radial and circumferential strain synchrony were measured with speckle-tracking echocardiography during biventricular pacing in a model of left ventricular (LV) volume overload.

METHODS

Heart block was established in 4 open-chest anesthetized pigs. Left ventricular volume overload was induced with an ascending aorta-LV apex conduit. Measurements included cardiac output by an aortic flow probe, the maximum derivative of LV pressure versus time (dP/dtmax), and transseptal pressure synchrony. Biventricular pacing was performed for combinations of 3 interventricular delays and 3 LV pacing sites. Speckle-tracking echocardiographic analysis was applied to short-axis images at the midpapillary LV for 9 pacing combinations. Strain and synchrony parameters were correlated with hemodynamics.

RESULTS

Increased cardiac output correlated with improved global circumferential strain (P = .002) but not changes in global radial strain or radial strain synchrony. Increased LV dP/dtmax was associated with improved circumferential strain in the septum (P < .001) and radial strain in the lateral wall (P = .046). Improved transseptal pressure synchrony was associated with improved global circumferential strain, but primarily in the septum (P < .001). Aortic valve closure occurred before peak radial strain in 62% of beats and before peak circumferential strain in 6%.

CONCLUSIONS

During acute LV volume overload, hemodynamic improvement with biventricular pacing was associated with improved circumferential strain primarily in the septum. Radial strain and radial strain synchrony did not correlate with improvement, possibly due to delayed systolic contraction. An increase in circumferential strain in the septum associated with optimum transseptal pressure synchrony suggested improvement by interventricular assist from the right ventricle.

Nuclear cardiology and heart failure

The prevalence of heart failure in the adult population is increasing. It varies between 1% and 2%, although it mainly affects elderly people (6-10% of people over the age of 65 years will develop heart failure). The syndrome of heart failure arises as a consequence of an abnormality in cardiac structure, function, rhythm, or conduction. Coronary artery disease is the leading cause of heart failure and it accounts for this disorder in 60-70% of all patients affected. Nuclear techniques provide unique information on left ventricular function and perfusion by gated-single photon emission tomography (SPECT). Myocardial viability can be assessed by both SPECT and PET imaging. Finally, autonomic dysfunction has been shown to increase the risk of death in patients with heart disease and this may be applicable to all patients with cardiac disease regardless of aetiology. MIBG scanning has a very promising prognostic value in patients with heart failure.