Evaluation of perfusion and viability in hypothermic non-beating isolated porcine hearts using cardiac MRI.

The donor heart undergoes degradation during hypothermic storage. An assessment of donor heart preservation is typically done with histological or biochemical methods that are not feasible in the clinical setting. We describe a method to study the donor heart using cardiac perfusion MRI that is potentially feasible for clinical use. Standard cardiectomy was performed in the pig model and the hearts were stored in normal saline at 5 degrees C. Imaging was performed by using a rapid gradient-echo sequence (FLASH) with saturation-recovery preparation for T1-weighting in the short axis and horizontal long axis views. Approximately 80 serial images were acquired at a rate of 1/s during administration of 0.006 mmol/ml Gd-DTPA (500 ml, 1 l/min). Signal intensity vs. time curves were generated for each heart and slice imaged and compared to a 0.006 mmol/ml Gd-DTPA reference. H&E stained biopsies of the LV, RV, and septum were also obtained. The mean duration of heart storage (N=10) was 8.8 h (range 4.2-19.2 h). Histologically, no differences were seen in H&E stained biopsies among hearts at different storage times. However cardiac MRI revealed a decrease in perfusion units in each subsequent heart tested after 4.2 h. (R=0.49). Average peak up-slope was used as a surrogate measure for flow capacity through the microvasculature and peak contrast enhancement was used as a measurement of viable microvasculature. The 4 h heart had 83% peak contrast enhancement of the reference standard, as compared to 44% for the 19.2 h heart. The decrease in peak enhancement is directly related to the duration of storage time. No correlation of peak up-slope of the intensity curve to storage time was found. This new application of cardiac MRI in the donor heart is applicable to: (1) assessing marginal hearts, (2) evaluating donor heart preservation techniques, and (3) correlating pre- to post-transplant viability.