Correlates of Tc-99m tetrofosmin pulmonary uptake in patients with coronary artery disease and subjected to high dose dipyridamole stress

ABSTRACT

The stress-lung-to-heart ratio [LHR] of uptake of the tracers during myocardial perfusion imaging [MPI] has been shown to have diagnostic significance for the severity of the disease and left ventricular [LV] dysfunction in patients with coronary artery disease [CAD]. On the other hand, high-dose dipyridamole [HDD] stress myocardial single photon emission computed tomography [SPECT] has greater accuracy for determination of CAD severity than standard dose dipyridamole [SDD] or exercise stress [EST]. To test whether the stress LHR of Tc-99m tetrofosmin [Tc-99m TF] uptake is a determinant of the severity of CAD and left ventricular dysfunction in patients with CAD and subjected to high-dose dipyridamole [HDD] stress. This retrospective study comprised 39 patients with angiographically-proved CAD [group I] and 8 subjects [group II] with negative MPI [gated rest and stress; one-day protocol] and normal coronaries that have been subjected to MPI using Tc-99m TF under HDD [0.84mg/kg over 4 min.]. The LHR of Tc-99m TF uptake was calculated by area of interest [AOI] analysis for the normalized myocardial and right lung counts from the immediate post-stress anterior chest view. The LV transient ischemic dilation [LVTID] was visually-interpreted; while the summed stress score [SSS] and rest LV function parameters were calculated. Further grouping of all subjects into 0-2 vessels CAD [group A] and main stem/3 vessel CAD [group B] was performed. The mean LHRs were 0.48 +/- 0.09 SD and 0.39 +/- 0.07 SD in groups I and II respectively [P>0.05]. The LHR of all subjects showed significant positive correlations with the SSS mid LV volumes and significant inverse correlation with LVEF [P<0.001 each] with no significant correlation with LVTID [P>0.05]. The LHRs were 0.44 +/- 0.08 SD and 0.57 +/- 0.08 SD in groups A and B respectively [P<0.001]. High dose dipyridamole [HDD] is a safe mode of stress to evaluate patients with CAD who are unable to exercise. The lung-to-heart ratio of Tc-99m tetrofosmin [immediately post HDD stress] seems to be a diagnostic marker to elicit the severity of CAD as well as the systolic and diastolic LV dysfunction in such patients