Changes in Myocardial Native T₁ and T₂ After Exercise Stress: A Noncontrast CMR Pilot Study

This study assessed changes in myocardial native T₁ and T₂ values after supine exercise stress in healthy subjects and in patients with suspected ischemia as potential imaging markers of ischemia.

With emerging data on the long-term retention of gadolinium in the body and brain, there is a need for an alternative noncontrast cardiovascular magnetic resonance (CMR)-based myocardial ischemia assessment.

Twenty-eight healthy adult subjects and 14 patients with coronary artery disease (CAD) referred for exercise stress and/or rest single-photon emission computed tomography/myocardial perfusion imaging (SPECT/MPI) for evaluation of chest pain were prospectively enrolled. Free-breathing myocardial native T₁ and T₂ mapping were performed before and after supine bicycle exercise stress using a CMR-compatible supine ergometer positioned on the MR table. Differences in T_{1 rest}, T_{2 rest} and T_{1 post-exercise}, T_{2 post-exercise} values were calculated as T₁ and T₂ reactivity, respectively.

The mean exercise intensity was 104 W, with exercise duration of 6 to 12 min. After exercise, native T₁ was increased in healthy subjects (p < 0.001). T₁ reactivity, but not T₂ reactivity, correlated with the rate-pressure product as the index of myocardial blood flow during exercise (r = 0.62; p < 0.001). In patients with CAD, T₁ reactivity was associated with the severity of myocardial perfusion abnormality on SPECT/MPI (normal: 4.9%; quartiles: 3.7% to 6.3%, mild defect: 1.2%, quartiles: 0.08% to 2.5%; moderate defect: 0.45%, quartiles: -0.35% to 1.4%; severe defect: 0.35%, quartiles: -0.44% to 0.8%) and had similar potential as SPECT/MPI to detect significant CAD (>50% diameter stenosis on coronary angiography). The area under the receiver-operating characteristic curve was 0.80 versus 0.72 (p = 0.40). The optimum cutoff value of T₁ reactivity for predicting flow-limiting stenosis was 2.5%, with a sensitivity of 83% and a specificity of 92%, a negative predictive value of 96%, a positive predictive value of 71%, and an area under the curve of 0.86.

Free-breathing stress/rest native T₁ mapping, but not T₂ mapping, can detect physiological changes in the myocardium during exercise. Our feasibility study in patients shows the potential of this technique as a method for detecting myocardial ischemia in patients with CAD without using a pharmacological stress agent.