Aim: To determine the factors associated with an inadequate response to adenosine infusion during cardiac stress magnetic resonance imaging (MRI).
Study design: It is a retrospective cohort study.
Introduction: Stress cardiac MRI is a highly accurate and non-invasive method to diagnose coronary artery disease (CAD). Stress MRI is performed by inducing stress with adenosine infusion. There is an increase in systemic and myocardial blood flow (MBF) with vasodilator agents. Capillaries are maximally dilated in a diseased artery and cannot sustain increased myocardial oxygen demand. It results in delayed delivery of contrast, which leads to an area of perfusion defect in the myocardium. These perfusion defects can be accurately seen by cardiovascular magnetic resonance (CMR) and help in the prognosis of patients.
Methods: A retrospective study on patients subjected to cardiac stress MRI was conducted in a Tertiary Care Cardiac Center from January 2019 to January 2022. In total, 99 patients underwent adenosine stress perfusion cardiac MRI. All patients received an adenosine infusion of 140 mcg/kg/min for 2 min. Subsequently, the dosage was increased by 20 mcg/kg/min every 2 min to a maximum of 210 mcg/kg/min until an adequate stress response was achieved. Adequate stress was defined as two or more of the following criteria: 1) Increase in heart rate >/= 10 beats per minute. 2) Decrease in systolic blood pressure SBP by >/= 10 mm Hg Symptoms like chest discomfort, breathlessness, and headache. Patients who satisfied two or more of the above criteria were labeled as responders and the patients who did not satisfy the above criteria with the maximum dose of 210 mcg/kg/min of adenosine infusion were labeled as non-responders. Multivariable logistic regression analysis with forward and backward stepwise selection was used to identify predictors in non-responders. Basic demographic variables with P value </= 0.2 were examined for inclusion in the model. A P value </= 0.05 was considered significant.
Results: Nine patients (9.1%) showed inadequate stress response to adenosine infusion even with a maximum dose of 210 mcg/kg/min. Multivariate logistic regression analysis showed that left ventricular end-diastolic volume (LVEDV) was a predictor of inadequate response to adenosine infusion.
Conclusion: Inadequate stress response to adenosine occurred in 9.1% of subjects with an infusion of 140-210 ug/kg/min. LVEDV is an independent and strong predictor in non-responders.
Keywords: Adenosine; cardiac stress MRI; left ventricular end-diastolic volume.