Validation of R Wave Voltage Endomyocardial Mapping to Assess Myocardial Fibrosis: Comparison with Thallium and Dobutamine Echocardiography in a Swine Model

The first aim of this study was to validate R wave voltage values measured with a catheter-based three-dimensional mapping system (NOGA, Biosense) against myocardial fibrosis in a swine model of ameroid placement. The second aim was to correlate the UPV maps with thallium uptake and low-dose dobutamine echocardiography. The electromechanical catheter mapping system can be used to guide endomyocardial laser therapy and direct gene delivery to the myocardium. The accuracy of R wave voltage in identifying myocardial fibrosis and its comparison with other imaging technologies against histopathology has not been fully investigated in an animal model. Ameroid constrictors were placed on 24 vessels in 14 swine. Wall motion abnormalities by echocardiography were detected in distribution of the constrictors at 22 +/- 10 days. Animals underwent rest and delayed thallium imaging, low-dose dobutamine echocardiography, and R wave voltage mapping. Animals were sacrificed, hearts were removed, 4-micron slices were stained, and fibrosis was quantified. Five control animals were studied to obtain segment normalization. There was significant agreement between each imaging modality and fibrosis by chi-square analysis. The correlation for segment normalized thallium uptake and segment normalized UPV score versus fibrosis were both significant (P < 0.001) with an r2 value of 0.362 vs. thallium, and r2 = 0.445 vs. UPV. The correlation was improved using log of UPV vs. fibrosis (r = 0.532). These results help validate R wave voltage mapping as an imaging technique to identify myocardial fibrosis.