Pressure-maximal coronary flow relationship in regionally stunned porcine myocardium

In view of variable results on maximal coronary blood flow in stunned myocardium, we studied the pressure-maximal coronary flow (PMCF) relationship in stunned myocardium in 12 anesthetized swine by using intracoronary adenosine (20 μg/kg). Subendocardial systolic segment shortening (SS) measured with sonomicrometry was 19 ± 5% (means ± SD) at baseline and 7 ± 6% (P < 0.01) at 30 min of reperfusion after 15 min of low-flow ischemia, at which time postsystolic shortening was present. Myocardial stunning increased the slope of the PMCF regression line (α(PMCF)) from 3.34 ± 1.03 to 3.89 ± 1.33 ml · min^-1 · mmHg^-1 (P < 0.01). Atrial pacing at 40 beats/min above spontaneous heart rate (n = 6) further reduced subendocardial SS to 6 ± 6% (P < 0.05). Dobutamine (4 μg · kg^-1 · min^-1; n = 6) increased subendocardial SS to 13 ± 5% (P < 0.05) and abolished postsystolic shortening. Both interventions left α(PMCF) unchanged. In conclusion, myocardial stunning was associated with an increase in α(PMCF) that most likely resulted from the decreased contractile function. The absence of an effect of dobutamine may be due to its predominant action on diastolic function.