Left ventricular dysfunction and disturbed O-2-utilization in stunned myocardium: influence of ischemic preconditioning

Objective: Myocardial dysfunction during postischemic reperfusion is freque ntly reported only in terms of left ventricular (LV) systolic properties. W e additionally assessed diastolic properties, the cardiovascular tone and i n particular. the relation between ventricular function and myocardial oxyg en consumption. Moreover, these measures are investigated after cardioprote ction via ischemic preconditioning (IP). However. this phenomenon is not fu lly understood. and therefore cardioprotective methods like ischemic precon ditioning might provide only insufficient protection. Methods: In a total o f 17 isolated rabbit hearts. perfused with an erythrocyte suspension (Hct 3 0%), we investigated the effect of 20 min low-flow ischemia also on diastol ic properties. coronary resistance and cardiac energetics (n = 9). During c ontrol and 30 min after the onset of reperfusion. LV systolic function was assessed in terms of aortic flow. dP/dt(max) and the end-systolic pressure- volume relation (ESPVR). Early relaxation was evaluated via dP/dt(min) and diastolic properties were assessed via the end-diastolic pressure-volume re lation (EDPVR), i.e. using the equation LVPed = c(.)exp(m(.)LVV(ed)), where c equals the LVPed-axis intercept and ni equals LV stiffness. In addition, coronary resistance (R-cor and the pressure-volume area (PVA) were calcula ted. Total oxygen consumption (MVO2) was calculated as well as the contract ile efficiency (E = inverse slope of the MVO2-PVA relation). In a second se ries (n = 8) the effect of ischemic preconditioning (3 min no-flow and 8 mi n reperfusion before the 20 min low-flow ischemia) was tested. Results: In the first series. systolic function was impaired during reperfusion: aortic flow to 32% of control. dP/dt(max) to 74% and the slope of ESPVR to 73%. E arly relaxation in terms of dP/dt(min) decreased to 76%. The slope of the E DPVR was steeper in stunned myocardium with an increase of the ventricular stiffness (in increased from 3.2 to 4.1) and with an upward shift of the ED PVR (c from 0.6 to 2.4 mmHg). Coronary resistance was increased (from 0.9 t o 1.4 mmHg/ml per min) and PVA was significantly decreased to 68%. whereas MVO2 was not indicating also a decrease in contractile efficiency E front 2 8 to 14%. In the second series, recovery of systolic function was significa ntly improved by IP compared with the first series (aortic flow 56% of prei schemic control. dP/dt(max) to 91% and ESPVR to 78%). LV stiffness m was al so slightly increased from 3.1 to 3.9 and again. c was elevated. indicating no beneficial effect for diastolic properties including dP/dt(min) (77%). But IP improved R-cor significantly (from 0.9 to only 1.0 mmHg/ml per min) and efficiency E to 21% (from 27% during control). Conclusion: Brief episod es of ischemia not only induce systolic but also diastolic and vascular stu nning at almost maintained MVO2. The decreased contractile efficiency clear iv indicates an impaired O-2-utilization of the contractile apparatus. Isch emic preconditioning did not improve diastolic function during reperfusion, but it provided protection with respect to vascular stunning and myocardia l energetics. (C) 2001 Elsevier Science BN. All rights reserved.