Improvement in left ventricular function following CRT is paralleled by a baseline increase in ejection fraction in response to dobutamine, according to a report in the American Heart Journal. Improvement in left ventricular function following cardiac resynchronization therapy (CRT) is paralleled by a baseline increase in ejection fraction in response to dobutamine -- myocardial contractile reserve -- according to a report in the December issue of the American Heart Journal.

"What is most important is some form of viability assessment," Dr. Jeroen J. Bax from Leiden University Medical Center, The Netherlands, told Reuters Health. "That can also be done with nuclear imaging or contrast-enhanced MRI."

Dr. Bax and colleagues investigated whether myocardial contractile reserve, assessed with echocardiography during low-dose dobutamine infusion, would predict left ventricular reverse remodeling and improvement in left ventricular function by CRT in both ischemic and non-ischemic patients.

Responders to CRT (defined as at least a 15 per cent reduction in left ventricular end-systolic volume) showed a greater increase in left ventricular ejection fraction (LVEF) during low-dose dobutamine infusion than did nonresponders, the authors report, and this improvement was directly related to the improvement in LVEF during follow-up after CRT.

A 7.5 per cent increase in LVEF during dobutamine infusion showed 76 per cent sensitivity and 86 per cent specificity in predicting CRT response at six-month follow-up, the report indicates.

Responders also showed significantly more left ventricular dyssynchrony than nonresponders at baseline.

In a multivariate analysis, both left ventricular dyssynchrony and contractile reserve were independent predictors of response to CRT.

"These data provide further support for the need of myocardial contractile reserve/viability assessment in the selection of CRT candidates," the authors conclude.

"The response to CRT depends probably on several issues, including cardiac dyssynchrony, viability and scar tissue, and LV lead positioning," Dr. Bax said. "All these factors will determine the response to CRT."

Dr. Bax added that further studies investigating prognosis and long-term outcomes of CRT are needed.