Effect of Intermittent High-Mechanical Index Impulses on Left Ventricular Strain

Background: Intermittent high-mechanical index (MI) impulses from a transthoracic ultrasound transducer are recommended for regional wall motion analysis and assessment of myocardial perfusion following intravenous administration of ultrasound enhancing agents (UEAs). High-MI impulses (>1.0) applied in this setting have also been shown to increase microvascular blood flow through a purinergic signaling pathway, but their effects on left ventricular (LV) myocardial function are unknown. Therefore, the aim of this study was to investigate the effect of transthoracic intermittent high-MI impulses during intravenous UEA infusion in patients with normal and abnormal resting systolic function.

Methods: Fifty patients referred for echocardiography to evaluate LV systolic function during continuous infusion of UEAs (Definity 3% infusion) were prospectively assigned to low-MI (<0.2) imaging alone (group 1) or low-MI (<0.2) imaging with intermittent high-MI impulses (five frames, 1.8 MHz, MI = 1.0-1.2) applied at least two times in each apical window to clear myocardial contrast (group 2). Global longitudinal strain (GLS) measurements were obtained at baseline before UEA administration and at 5-min intervals up to 10-min after infusion completion.

Results: There were no differences between groups with respect to age, gender, resting GLS, biplane LV ejection fraction, or cardiac risk factors. Resting GLS in group 1 was -15.5 ± 5.2% before UEA infusion and -15.5 ± 5.4% at 10 min after UEA infusion. In comparison, GLS increased in group 2 (-15.3 ± 5.0 before infusion and -16.8 ± 4.8% at 10 min, P < .00001). Improvements in GLS were seen in patients with normal and abnormal systolic function. Regional analysis demonstrated that the increase in strain in patients with abnormal LV ejection fractions was primarily in the apical segments (-12.0 ± 2.7% before infusion and -13.4 ± 3.4% at 10 min, P = .001).

Conclusions: High-MI impulses during infusion of a commercially available contrast agent can improve LV systolic function and may have therapeutic effect in patients with LV dysfunction.