Noninvasive quantification of the contractile reserve of stunned myocardium by ultrasonic strain rate and strain

Background-We sought to investigate ultrasonic strain rate and strain as ne w indices to quantify the contractile reserve of stunned myocardium during dobutamine infusion. Methods and Results-Stunning of the left ventricular posterior wall was ind uced in 9 closed-chest pigs after 30 minutes of severe hypoperfusion follow ed by 60 minutes of reperfusion of the left circumflex coronary artery terr itory. A second group of 7 animals had no coronary occlusion and served as normal controls. An incremental dobutamine infusion protocol was used in bo th groups. Changes in regional radial function were monitored by use of ult rasound-derived maximal systolic radial strain rate (SR) and systolic strai n (epsilon). In the control group, dobutamine induced an increase in both S R and maximal dP/dt, which correlated linearly (r = 0.85). Conversely, epsi lon values increased at low doses of dobutamine (2.5 to 5 mug.kg(-1).min(-1 )) but decreased during higher infusion rates (10 to 20 mug.kg(-1).min(-1)) . During circumflex hypoperfusion, SR and epsilon of the posterior wall dec reased from 5.0 +/- 0.3 s(-1) and 63 +/- 6% to 2.9 +/- 0.3 s(-1) and 27 +/- 4%, respectively (P < 0.01). After 60 minutes of reperfusion, SR and <epsi lon> failed to fully resume because of stunning, averaging 3.6 +/- 0.2 s(-1 ) and 35 +/- 3%, respectively (P = 0.12 versus ischemia, P < 0.05 versus ba seline). During dobutamine infusion, SR increased at 5 <mu>g.kg(-1).min(-1) and exceeded baseline values at 20 mug.kg(-1).min(-1) (P < 0.05), whereas <epsilon> increased only at high doses and remained below baseline levels ( P < 0.05). Conclusions-The changes in regional function of stunned myocardium during i notropic stimulation could be characterized by use of ultrasonic deformatio n parameters. During dobutamine infusion, strain-rate values quantified the contractile reserve better than strain values.