Non-invasive CMR-Based Quantification of Myocardial Power and Efficiency Under Stress and Ischemic Conditions in Landrace Pigs

Background: Myocardial efficiency should be maintained stable under light-to-moderate stress conditions, but ischemia puts the myocardium at risk for impaired functionality. Additionally, the measurement of such efficiency typically requires invasive heart catheterization and exposure to ionizing radiation. In this work, we aimed to non-invasively assess myocardial power and the resulting efficiency during pharmacological stress testing and ischemia induction.Methods: In a cohort of n = 10 healthy Landrace pigs, dobutamine stress testing was performed, followed by verapamil-induced ischemia alongside cardiac magnetic resonance (CMR) imaging. External myocardial power, internal myocardial power, and myocardial efficiency were assessed non-invasively using geometrical and functional parameters from CMR volumetric as well as blood flow and pressure measurements.Results: External myocardial power significantly increased under dobutamine stress [2.3 (1.6–3.1) W/m2 vs. 1.3 (1.1–1.6) W/m2, p = 0.005] and significantly decreased under verapamil-induced ischemia [0.8 (0.5–0.9) W/m2, p = 0.005]. Internal myocardial power [baseline: 5.9 (4.6–8.5) W/m2] was not affected by dobutamine [7.5 (6.9–9.0) W/m2, p = 0.241] nor verapamil [5.8 (4.7–8.8) W/m2, p = 0.878]. Myocardial efficiency did not change from baseline to dobutamine [21% (15–27) vs. 31% (20–44), p = 0.059] but decreased significantly during verapamil-induced ischemia [10% (8–13), p = 0.005].Conclusion: In healthy Landrace pigs, dobutamine stress increased external myocardial power, whereas myocardial efficiency was maintained stable. On the contrary, verapamil-induced ischemia substantially decreased external myocardial power and myocardial efficiency. Non-invasive CMR was able to quantify these efficiency losses and might be useful for future clinical studies evaluating the effects of therapeutic interventions on myocardial energetics.

Theophylline and Caffeine as Alternatives During an Aminophylline Shortage

The latest aminophylline shortage has prompted a need for alternative reversal agents for pharmacological stress testing. Cardiac stress testing is common for diagnosis and prognosis in patients with coronary heart disease. Options for pharmacological stress test agents include adenosine, regadenoson, dipyridamole, and dobutamine, whereas aminophylline is the recommended reversal agent. Adenosine and dobutamine can be used as alternatives to regadenoson and dipyridamole to decrease or eliminate the use of aminophylline. Alternatives to aminophylline include theophylline and caffeine. It is important to efficiently identify alternatives during a drug shortage to maintain optimal patient outcomes.

Pharmacologic Stress Testing

Pharmacological stress testing plays an important role in patient management. Pharmacologic stress agents (adenosine, dipyridamole, regadenoson, dobutamine) produce coronary hyperemia, which is at least as high as that achieved by maximal exercise, by a completely different set of mechanisms than that achieved during exercise. Regadenoson, a relatively newer agent, offers ease of administration and fewer side effects than older stress agents and has become the agent of choice in many stress laboratories. The choice of the stress agent should be individualized based on its indications, contraindications and safety profile. The diagnostic accuracy of pharmacological stress testing for significant coronary artery disease detection is comparable to or exceeds that of exercise myocardial perfusion imaging.