Cardiovascular magnetic resonance feature tracking in pigs: a reproducibility and sample size calculation study

Post-Myocardial Infarction Remodeling and Hyperkinetic Remote Myocardium in Sheep Measured by Cardiac MRI Feature Tracking

BACKGROUND

Cardiac MRI feature tracking (FT) allows objective assessment of segmental left ventricular (LV) function following a myocardial infarction (MI), but its utilization in sheep, where interventions can be tested, is lacking.

PURPOSE

To apply and validate FT in a sheep model of MI and describe post-MI LV remodeling.

STUDY TYPE

Animal model, longitudinal.

ANIMAL MODEL

Eighteen lambs (6 months, male, n = 14; female, n = 4; 25.2 ± 4.5 kg).

FIELD STRENGTH/SEQUENCE

Two-dimensional balanced steady-state free precession (bSSFP) and 3D inversion recovery fast low angle shot (IR-FLASH) sequences at 3 T.

ASSESSMENT

Seven lambs underwent test-retest imaging to assess FT interstudy reproducibility. MI was induced in the remaining 11 by coronary ligation with MRI being undertaken before and 15 days post-MI. Injury size was measured by late gadolinium enhancement (LGE) and LV volumes, LV mass, ejection fraction (LVEF), and wall thickness (LVWT) were measured, with FT measures of global and segmental radial, circumferential, and longitudinal strain.

STATISTICAL TESTS

Sampling variability, inter-study, intra and interobserver reproducibility were assessed using Pearson's correlation, Bland-Altman analyses, and intra-class correlation coefficients (ICC). Diagnostic performance of segmental strain to predict LGE was assessed using receiver operating characteristic curve analysis. Significant differences were considered P < 0.05.

RESULTS

Inter-study reproducibility of FT was overall good to excellent, with global strain being more reproducible than segmental strain (ICC = 0.89-0.98 vs. 0.77-0.96). MI (4.0 ± 3.7% LV mass) led to LV remodeling, as evident by significantly increased LV volumes and LV mass, and significantly decreased LVWT in injured regions, while LVEF was preserved (54.9 ± 6.9% vs. 55.6 ± 5.7%; P = 0.778). Segmental circumferential strain (CS) correlated most strongly with LGE. Basal and mid- CS increased significantly, while apical CS significantly decreased post-MI.

DATA CONCLUSION

FT is reproducible and compensation by hyperkinetic remote myocardium may manifest as overall preserved global LV function.

EVIDENCE LEVEL

N/A TECHNICAL EFFICACY: Stage 2.

Hypothermia as an adjunctive therapy to percutaneous intervention after ST-elevation myocardial infarction-Effects on regional myocardial contractility

BACKGROUND

The effects of endovascular therapeutic hypothermia (ETH) in ST-elevation myocardial infarction (STEMI) regional contractility are unknown, and its impact on segmental contractility has still not been evaluated. We sought to evaluate segmental myocardial strain after ETH adjuvant to percutaneous coronary intervention (PCI) in STEMI.

METHODS

We included patients who underwent 1.5T cardiovascular magnetic resonance exams 5 and 30 days after acute anterior or inferior STEMI in a previous randomized trial. Left ventricle (LV) strain was evaluated on infarcted, adjacent, and remote myocardium. Segmental circumferential (CS) and radial strains (RS) were measured using feature-tracking imaging. Repeated measures of analysis of variance were used for comparisons within time and treatment.

RESULTS

Forty patients were divided into hypothermia (ETH, n = 29) and control (n = 11) groups, with 5210 LV segments. In ETH infarcted areas, RS (11.2 ± 16 vs 14.8 ± 15.2, p = 0.001) and CS (-5.4 ± 11.1 vs -8 ± 11.1, p = 0.001) showed recovery from 5-30 days compared to controls (11.4 ± 14 vs 13.1 ± 1 6.8, p = 0.09; -6.5 ± 10.6 vs -6.4 ± 12.5, p = 0.94). In control remote areas, RS (28 ± 18 vs 31.7 ± 18.5, p = 0.001) and CS (-15.5 ± 10.7 vs -17.1 ± 9, p = 0.001) improved from 5-30 days compared to ETH (28.6 ± 18.6 vs 29 ± 20, p = 0.44; -15.2 ± 10.4 vs -15.3 ± 10.6, p = 0.82). Transmural infarcted areas in ETH improved RS (11.8 ± 13.2 vs 8.17 ± 14.7, p = 0.001) and CS (-6.1 ± 10.9 vs.-3.1 ± 11.3, p = 0.001) compared to controls, with better contractility at 30 days.

CONCLUSION

In anterior or inferior STEMI patients, ETH adjuvant to PCI is associated with significant improvement in RS and CS of infarcted areas, including transmural segments, but not in remote area. This might further increase our pathophysiological knowledge on early LV remodeling and ultimately suggest potential clinical value.

AVAILABILITY OF DATA AND MATERIALS

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Evaluating pulmonary stenosis and regurgitation impact on cardiac strain and strain rate in a porcine model via magnetic resonance feature tracking

BACKGROUND

Pulmonary stenosis (PS) is common in congenital heart disease and an integral finding in Tetralogy of Fallot (TOF). Pulmonary regurgitation (PR) is more commonly found following surgery in repaired TOF. We aimed to evaluate the haemodynamic effects of PS and PR on cardiac physiology in a porcine model using cardiac magnetic resonance-based feature tracking (CMR-FT) deformation imaging.

METHODS

CMR-FT was performed in 14 pigs before and 10-12 weeks after surgery. Surgery included either pulmonary artery banding to simulate PS (n = 7), or an incision to the pulmonary valve to simulate PR (n = 7). CMR-FT assessment included left and right ventricular global longitudinal (LV/RV GLS) and LV circumferential (GCS) strain and strain rates (SR) as well as left and right atrial reservoir/conduit/booster pump (LA/RA Es, Ee, Ea) strain and SR.

RESULTS

RV GLS was significantly reduced following PS compared to PR induction (PS -7.51 vs. PR -23.84, p < 0.001). RV GLS improved after induction of PR (before - 20.50 vs. after - 23.84, p = 0.018) as opposed to PS (before - 11.73 vs. after - 7.51, p = 0.128). Similarly, RA Es (PS 14.22 vs. PR 27.34, p = 0.017) and Ee (PS 8.65 vs. PR 20.51, p = 0.004) were decreased in PS compared to PR with detrimental impact of PS (Es before 23.20 vs. after 14.22, p = 0.018, Ee before 15.04 vs. after 8.65, p = 0.028) but not PR (Es before 31.65 vs. after 27.34, p = 0.176, Ee before 20.63 vs. after 20.51, p = 0.499).

CONCLUSIONS

In a porcine model of RV pressure vs. volume overload, increased after- but not preload shows detrimental impact on RV and RA physiology.

Reliability of left ventricular hemodynamic forces derived from feature-tracking cardiac magnetic resonance

BACKGROUND

Hemodynamic forces (HDF) analysis has been proposed as a method to quantify intraventricular pressure gradients, however data on its reliability are still scanty. Thus, the aim of this study is to assess the reliability of HDF parameters derived from cardiac magnetic resonance (CMR).

METHODS

CMR studies of 25 athletes were analysed by two independent observers and then re-analysed by the same observer one week apart. Intraclass Correlation Coefficient (ICC [95% CI]) and Bland-Altman plots were used to assess association, agreement, and bias of the longitudinal (A-B) HDF, transverse (L-S) HDF, and Impulse Angle. The sample size required to detect a relative change in the HDF parameters was also calculated.

RESULTS

In terms of inter-observer variability, there was a good correlation for the A-B and L-S (ICC 0.85 [0.67-0.93] and 0.86 [0.69-0.94]; p<0.001 for both, respectively) and a moderate correlation for the Impulse Angle (ICC 0.73 [0.39-0.87]; p = 0.001). For intra-observer variability, A-B and L-S showed excellent correlation (ICC 0.91 [0.78-0.93] and 0.93 [0.83-0.97]; p<0.001 for both, respectively). Impulse Angle presented good correlation (ICC 0.80 [0.56-0.90]; p<0.001). Frame selection and aortic valve area measurements were the most vulnerable step in terms of reliability of the method. Sample size calculation to detect relative changes ranged from n = 1 to detect a 15% relative change in Impulse Angle to n = 171 for the detection of 10% relative change in A-B HDF.

CONCLUSIONS

The results of this study showed a low inter- and intra-observer variability of HDF parameters derived from feature-tracking CMR. This provides the fundamental basis for their use both in research and clinical practice, which could eventually lead to the detection of significant changes at follow-up studies.

Pulmonary 4D-flow MRI imaging in landrace pigs under rest and stress

4D-flow MRI is a promising technique for assessing vessel hemodynamics. However, its utilization is currently limited by the lack of reference values, particularly for pulmonary vessels. In this work, we have analysed flow and velocity in the pulmonary trunk (PT), left and right pulmonary arteries (LPA and RPA, respectively) in Landrace pigs at both rest and stress through the software MEVISFlow. Nine healthy Landrace pigs were acutely instrumented closed-chest and transported to the CMR facility for evaluation. After rest measurements, dobutamine was administered to achieve a 25% increase in heart rate compared to rest. 4D-flow MRI images have been analysed through MEVISFlow by two independent observers. Inter- and intra-observer reproducibility was quantified using intraclass correlation coefficient. A significant difference between rest and stress regarding flow and velocity in all the pulmonary vessels was observed. Mean flow increased 55% in PT, 75% in LPA and 40% in RPA. Mean peak velocity increased 55% in PT, 75% in LPA and 66% in RPA. A good-to-excellent reproducibility was observed in rest and stress for flow measurements in all three arteries. An excellent reproducibility for velocity was found in PT at rest and stress, a good one for LPA and RPA at rest, while poor reproducibility was found at stress. The current study showed that pulmonary flow and velocity assessed through 4D-flow MRI follow the physiological alterations during cardiac cycle and after stress induced by dobutamine. A clinical translation to assess pulmonary diseases with 4D-flow MRI under stress conditions needs investigation.

Colchicine added to standard therapy further reduces fibrosis in pigs with myocardial infarction

BACKGROUND

The anti-inflammatory drug colchicine improves the outcome of patients with myocardial infarction (MI). As an intense inflammatory and fibrotic response after MI may lead to scar expansion and left ventricular (LV) remodeling, the clinical benefit of colchicine could be related to a positive effect on the infarct scar and LV remodeling.

METHODS

Pigs underwent left anterior descending artery occlusion through an angioplasty balloon for 90 min and were then randomized into two groups: standard therapy [ACE inhibitor, beta blocker, mineralocorticoid receptor antagonist (MRA), aspirin] plus colchicine (n = 14) or standard therapy alone (n = 13). The pigs were treated for 30 days and underwent two cardiac magnetic resonance (CMR) scans at 72 h and 30 days. The pigs were then sacrificed the day after the second CMR. The primary efficacy end point was the extent of fibrosis in the infarct zone (calculated on eight samples from this zone and averaged).

RESULTS

In the hearts explanted after 31 days, pigs in the colchicine group had less fibrosis in the infarct zone than the other animals [41.6% (20.4-51.0) vs. 57.4% (42.9-66.5); P = 0.022]. There was a trend toward a higher myocardial salvage index (MSI; an index of the efficacy of revascularization) in pigs on colchicine (P = 0.054). Conversely, changes in LV volumes, ejection fraction and mass did not differ between groups.

CONCLUSION

Colchicine therapy for 1 month after reperfused MI further reduces myocardial fibrosis when added to standard therapy, while it does not have additional effects on LV remodeling.

Hemoglobin A1c in type 2 diabetes mellitus patients with preserved ejection fraction is an independent predictor of left ventricular myocardial deformation and tissue abnormalities

BACKGROUND

Early detection of subclinical myocardial dysfunction in patients with type 2 diabetes mellitus (T2DM) is essential for preventing heart failure. This study aims to search for predictors of left ventricular (LV) myocardial deformation and tissue abnormalities in T2DM patients with preserved ejection fraction by using CMR T1 mapping and feature tracking.

METHODS

70 patients and 44 sex- and age-matched controls (Cs) were recruited and underwent CMR examination to obtain LV myocardial extracellular volume fraction (ECV) and global longitudinal strain (GLS). The patients were subdivided into three groups, including 19 normotensive T2DM patients (G1), 19 hypertensive T2DM patients (G2) and 32 hypertensive patients (HT). The baseline biochemical indices were collected before CMR examination.

RESULTS

LV ECV in T2DM patients was significantly higher than that in Cs (30.75 ± 3.65% vs. 26.33 ± 2.81%; p < 0.05). LV GLS in T2DM patients reduced compared with that in Cs (-16.51 ± 2.53% vs. -19.66 ± 3.21%, p < 0.001). In the subgroup analysis, ECV in G2 increased compared with that in G1 (31.92 ± 3.05% vs. 29.59 ± 3.90%, p = 0.032) and that in HT, too (31.92 ± 3.05% vs. 29.22 ± 6.58%, p = 0.042). GLS in G2 significantly reduced compared with that in G1 (-15.75 ± 2.29% vs. -17.27 ± 2.57%, p < 0.05) and in HT, too (-15.75 ± 2.29% vs. -17.54 ± 3.097%, p < 0.05). In T2DM group, including both G1 and G2, hemoglobin A1c (HbA1c) can independently forecast the increase in ECV (β = 0.274, p = 0.001) and decrease in GLS (β = 0.383, p = 0.018).

CONCLUSIONS

T2DM patients with preserved ejection fraction show increased ECV but deteriorated GLS, which may be exacerbated by hypertension of these patients. Hemoglobin A1c is an index that can independently predict T2DM patients' LV myocardial deformation and tissue abnormalities.

Feature tracking strain analysis detects the onset of regional diastolic dysfunction in territories with acute myocardial injury induced by transthoracic electrical interventions

Electric interventions are used to terminate arrhythmia. However, myocardial injury from the electrical intervention can follow unique pathways and it is unknown how this affects regional ventricular function. This study investigated the impact of transthoracic electrical shocks on systolic and diastolic myocardial deformation. Ten healthy anaesthetized female swine received five transthoracic shocks (5 × 200 J) and six controls underwent a cardiovascular magnetic resonance exam prior to and 5 h after the intervention. Serial transthoracic shocks led to a global reduction in both left (LV, - 15.6 ± 3.3% to - 13.0 ± 3.6%, p < 0.01) and right ventricular (RV, - 16.1 ± 2.3% to - 12.8 ± 4.2%, p = 0.03) peak circumferential strain as a marker of systolic function and to a decrease in LV early diastolic strain rate (1.19 ± 0.35/s to 0.95 ± 0.37/s, p = 0.02), assessed by feature tracking analysis. The extent of myocardial edema (ΔT1) was related to an aggravation of regional LV and RV diastolic dysfunction, whereas only RV systolic function was regionally associated with an increase in T1. In conclusion, serial transthoracic shocks in a healthy swine model attenuate biventricular systolic function, but it is the acute development of regional diastolic dysfunction that is associated with the onset of colocalized myocardial edema.

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.

Cardiovascular magnetic resonance-derived left ventricular mechanics-strain, cardiac power and end-systolic elastance under various inotropic states in swine

BACKGROUND

Cardiovascular magnetic resonance (CMR) strain imaging is an established technique to quantify myocardial deformation. However, to what extent left ventricular (LV) systolic strain, and therefore LV mechanics, reflects classical hemodynamic parameters under various inotropic states is still not completely clear. Therefore, the aim of this study was to investigate the correlation of LV global strain parameters measured via CMR feature tracking (CMR-FT, based on conventional cine balanced steady state free precession (bSSFP) images) with hemodynamic parameters such as cardiac index (CI), cardiac power output (CPO) and end-systolic elastance (Ees) under various inotropic states.

METHODS

Ten anaesthetized, healthy Landrace swine were acutely instrumented closed-chest and transported to the CMR facility for measurements. After baseline measurements, two steps were performed: (1) dobutamine-stress (Dobutamine) and (2) verapamil-induced cardiovascular depression (Verapamil). During each protocol, CMR images were acquired in the short axisand apical 2Ch, 3Ch and 4Ch views. MEDIS software was utilized to analyze global longitudinal (GLS), global circumferential (GCS), and global radial strain (GRS).

RESULTS

Dobutamine significantly increased heart rate, CI, CPO and Ees, while Verapamil decreased them. Absolute values of GLS, GCS and GRS accordingly increased during Dobutamine infusion, while GLS and GCS decreased during Verapamil. Linear regression analysis showed a moderate correlation between GLS, GCS and LV hemodynamic parameters, while GRS correlated poorly. Indexing global strain parameters for indirect measures of afterload, such as mean aortic pressure or wall stress, significantly improved these correlations, with GLS indexed for wall stress reflecting LV contractility as the clinically widespread LV ejection fraction.

CONCLUSION

GLS and GCS correlate accordingly with LV hemodynamics under various inotropic states in swine. Indexing strain parameters for indirect measures of afterload substantially improves this correlation, with GLS being as good as LV ejection fraction in reflecting LV contractility. CMR-FT-strain imaging may be a quick and promising tool to characterize LV hemodynamics in patients with varying degrees of LV dysfunction.