Assessment of Myocardial Function During Blood Pressure Manipulations Using Feature Tracking Cardiovascular Magnetic Resonance

Abstract

Background: Coronary autoregulation is a feedback system, which maintains near-constant myocardial blood flow over a range of mean arterial pressure (MAP). Yet in emergency or peri-operative situations, hypotensive or hypertensive episodes may quickly arise. It is not yet established how rapid blood pressure changes outside of the autoregulation zone (ARZ) impact left (LV) and right ventricular (RV) function. Using cardiovascular magnetic resonance (CMR) imaging, measurements of myocardial tissue oxygenation and ventricular systolic and diastolic function can comprehensively assess the heart throughout a range of changing blood pressures.Design and methods: In 10 anesthetized swine, MAP was varied in steps of 10–15 mmHg from 29 to 196 mmHg using phenylephrine and urapidil inside a 3-Tesla MRI scanner. At each MAP level, oxygenation-sensitive (OS) cine images along with arterial and coronary sinus blood gas samples were obtained and blood flow was measured from a surgically implanted flow probe on the left anterior descending coronary artery. Using CMR feature tracking-software, LV and RV circumferential systolic and diastolic strain parameters were measured from the myocardial oxygenation cines.Results: LV and RV peak strain are compromised both below the lower limit (LV: Δ1.2 ± 0.4%, RV: Δ4.4 ± 1.2%, p < 0.001) and above the upper limit (LV: Δ2.1 ± 0.4, RV: Δ5.4 ± 1.4, p < 0.001) of the ARZ in comparison to a baseline of 70 mmHg. LV strain demonstrates a non-linear relationship with invasive and non-invasive measures of oxygenation. Specifically for the LV at hypotensive levels below the ARZ, systolic dysfunction is related to myocardial deoxygenation (β = −0.216, p = 0.036) in OS-CMR and both systolic and diastolic dysfunction are linked to reduced coronary blood flow (peak strain: β = −0.028, p = 0.047, early diastolic strain rate: β = 0.026, p = 0.002). These relationships were not observed at hypertensive levels.Conclusion: In an animal model, biventricular function is compromised outside the coronary autoregulatory zone. Dysfunction at pressures below the lower limit is likely caused by insufficient blood flow and tissue deoxygenation. Conversely, hypertension-induced systolic and diastolic dysfunction points to high afterload as a cause. These findings from an experimental model are translatable to the clinical peri-operative environment in which myocardial deformation may have the potential to guide blood pressure management, in particular at varying individual autoregulation thresholds.

Diagnostic performance of cardiac magnetic resonance segmental myocardial strain for detecting microvascular obstruction and late gadolinium enhancement in patients presenting after a ST-elevation myocardial infarction

“…We would explain the higher diagnostic performance in our cohort mainly due to a higher robustness to outliers/wrong values. SLS is assessed in 3 long axis slices, every segment is depicted exactly once, while in a SAX stack every segment is depicted at least twice and results are averaged over the segment, as we also observed in our myocarditis cohort ( 6 ). This could also be different in patients with smaller infarct sizes, with only endocardial layer affected, where SLS could be more important.…”

“…First, to characterize segmental CMR-FT measurements based on the presentation of co-localized MVO or LGE, segmental strain values were categorized into the three groups LGE+/MVO+, LGE+/MVO–, and LGE–. To compare these three groups, a mixed linear model was fitted with the lmer and emmeans ( 6 , 12 ) functions accounting for multiple measurements per patient by including subject identification as a random intercept and reported as mean and standard error.…”

Insights Into Myocardial Oxygenation and Cardiovascular Magnetic Resonance Tissue Biomarkers in Heart Failure With Preserved Ejection Fraction

“…46 In addition, OS-CMR has been compared to invasive blood and coronary flow measures in animals. [47][48][49] Nevertheless, as this is a developing technique further validation is required, along with additional comparisons to pharmacological stress testing. 8,44…”

Combined Analysis of Myocardial Deformation and Oxygenation Detects Inducible Ischemia Unmasked by Breathing Maneuvers in Chronic Coronary Syndrome

“…The association of changes of OS-CMR-derived myocardial oxygenation with regional myocardial function has not been studied so far in cardiovascular patients. In swine, this combined analysis was performed and FT measurements from OS images were shown to be linked with myocardial deoxygenation at low perfusion pressures ( 11 ). With the use of FT software, the OS cines used for oxygenation analysis can be simultaneously interrogated to assess strain parameters.…”