Purpose: Cardiac shunt study by first pass radionuclide angiography (FPRNA) used to be performed by gamma camera with high sensitive collimator. With the use of dedicated gamma camera using high resolution imaging, first pass dynamic studies have been infrequently performed and almost neglected. There is still a need for accurate cardiac shunt measurement by cardiologists for reassurance of shunt size by another modality in addition to echocardiography for therapeutic decision making.
Methods: During 1.2010- 9.2014, we prospectively studied subjects referred for FPRNA to quantitate left to right shunt. The patients were referred by cardiologists following echocardiographic and doppler study. The FPRNA was done by rapid IV injection of 10-25 mCi of Tc 99m pertechnetate on dedicated gamma camera with general purpose collimator. Muga study was performed for assessing RV and LV function when needed. The quantitative assessment of left to right shunt by FPRNA was done by creating region of interest on both lungs and calculation of areas under gamma fit, using the formula QP/QS (pulmonary to systemic flow ratio).
Results: There were 203 patients, mean age 25.5±22.7 years, 55% were male. There were 38 (19%) with PFO, 126 (62%) with ASD, 31(15%) with VSD and others. The assessment of shunt by echo Doppler was graded as suspected or minimal (grade 0), small shunt (grade 1) and significant (grade 2). The shunt size by FPRNA was graded as no shunt (grade 0) (QP/QS = 1:1 - 1.15:1), small shunt (grade 1) when QP/QS>1.15:1- 1.49:1, and significant shunt when QP/QS ≥ 1.5:1. There was substantial agreement of shunt size by echo and QP/QS (kappa= 0.70, p< 0.0001). The shunt size agreement was better with ASD and PFO than with VSD (kappa 0.716 and 0.45 respectively). LV enlargement improved agreement of VSD size.
Conclusion: Quantitative analysis of cardiac left to right shunt by FPRNA using gamma camera with multipurpose collimator is feasible. It might have an added value in therapeutic decision making.
