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.

Image-Based Computational Model Predicts Dobutamine-Induced Hemodynamic Changes in Patients With Aortic Coarctation

Background: Pharmacological stress testing can help to uncover pathological hemodynamic conditions and is, therefore, used in the clinical routine to assess patients with structural heart diseases such as aortic coarctation with borderline indication for treatment. The aim of this study was to develop and test a reduced-order model predicting dobutamine stress induced pressure gradients across the coarctation. Methods: The reduced-order model was developed based on n=21 imaging data sets of patients with aortic coarctation and a meta-analysis of subjects undergoing dobutamine stress testing. Within an independent test cohort of n=21 patients with aortic coarctation, the results of the model were compared with dobutamine stress testing during catheterization. Results: In n=19 patients responding to dobutamine stress testing, pressure gradients across the coarctation during dobutamine stress increased from 15.7±5.1 to 33.6±10.3 mm Hg (paired t test, P <0.001). The model-predicted pressure gradients agreed with catheter measurements with a mean difference of −2.2 mm Hg and a limit of agreement of ±11.16 mm Hg according to Bland-Altman analysis. Significant equivalence between catheter-measured and simulated pressure gradients during stress was found within the study cohort (two 1-sided tests of equivalence with a noninferiority margin of 5.0 mm Hg, 33.6±10.33 versus 31.5±11.15 mm Hg, P =0.021). Conclusions: The developed reduced-order model can instantly predict dobutamine-induced hemodynamic changes with accuracy equivalent to heart catheterization in patients with aortic coarctation. The method is easy to use, available as a web-based calculator, and provides a promising alternative to conventional stress testing in the clinical routine. Registration: URL: https://www.clinicaltrials.gov . Unique identifier: NCT02591940.

Bezold–Jarisch reflex-mediated asystole during dobutamine stress testing: a case report

Background The Bezold–Jarisch reflex (BJR) is a cardioinhibitory parasympathetic response to activation of ventricular mechanoreceptors, which can result in bradycardia, atrioventricular block, or asystole. This phenomenon has been triggered by acute myocardial ischaemia, intra-arterial nitroglycerine use, natriuretic peptides, and with exceptional rarity, in middle-aged women only, by dobutamine infusion during stress echocardiography. Case summary We present the case of a 61-year-old woman who suffered a 5.1-s sinus pause during her 20 μg/kg/min infusion of dobutamine. Recovery was immediate following termination of dobutamine infusion. Concurrent echocardiography was normal, and subsequent cardiac catheterization and electrophysiologic study were normal. Discussion This is the fifth documented case of a severe BJR causing asystole during dobutamine infusion, which adds to the accumulating evidence supporting the benign nature of the condition.

A physiologist observing and reporting supra-pharmacologic dobutamine stress testing: can we trust them, and can we trust the results?

In a study, published in this issue of Echo Research and Practice, Ntoskas et al. retrospectively analyzed the safety of a cardiac physiologist performing, and interpreting, Dobutamine stress echocardiography (DSE) in of 300 patients undergoing DSE for the detection of inducible reversible ischemia, myocardial viability and valvular heart disease. While safety during the tests themselves did not appear to be compromised with this unsupervised approach, the interpretation of these DSEs causes concerns regarding broad patient safety relative to misread results.