Sublingual glyceryl trinitrate given during adenosine sestamibi myocardial perfusion imaging causes apparent transient ischaemic dilation in a propensity-matched analysis

OBJECTIVES: Administration of sublingual glyceryl trinitrate (GTN) prior to resting radiotracer injection during myocardial perfusion imaging (MPI) has been advocated to aid detection of viable myocardium and increase the extent of reversible perfusion defects. However, GTN is also known to reduce resting left ventricular volume and could thus increase the transient ischaemic dilation (TID) ratio, independently of severe or extensive coronary artery disease. We aimed to determine if GTN administration causes an increase in the TID ratio. METHODS: Causal inference using propensity score matched analysis was used to assess the effect of GTN on TID ratios in subjects undergoing adenosine sestamibi MPI. RESULTS: From 597 consecutive patients undergoing MPI, we selected a treatment group of 51 who received 400 μg of sublingual GTN before resting sestamibi injection and 51 propensity score matched controls. Mean TID ratios were 1.24 in treated subjects and 1.10 in controls (mean difference 0.15; 95% CI, 0.05-0.25; P = 0.0018). The mean difference in TID ratio fell progressively in each quartile of time elapsed between GTN administration and image acquisition. The proportion with TID ratios equal and greater than an abnormal threshold of 1.39 was 17.6% among the treated and 0% in controls ( P = 0.0010). The effect on TID ratio was not restricted to those with moderate-to-severe stress perfusion defects or accompanied by greater reversible perfusion defects. CONCLUSIONS: There is evidence of a cause-and-effect relationship between administering GTN before resting sestamibi injection and increased TID ratio on MPI. This may be a source of misleading false positive TID findings.