Regional wall function before and after acute myocardial infarction; an experimental study in pigs

Precision imaging of cardiac function and scar size in acute and chronic porcine myocardial infarction using ultrahigh-field MRI

BACKGROUND

7 T cardiac magnetic resonance imaging (MRI) studies may enable higher precision in clinical metrics like cardiac function, ventricular mass, and more. Higher precision may allow early detection of functional impairment and early evaluation of treatment responses in clinical practice and pre-clinical studies.

METHODS

Seven female German Landrace pigs were scanned prior to and at three time points (3-4 days, 7-10 days, and ~60 days) post myocardial infarction using a whole body 7 T system and three radiofrequency (RF) coils developed and built in-house to accompany animal growth.

RESULTS

The combination of dedicated RF hardware and 7 T MRI enables a longitudinal study in a pig model of acute and chronic infarction, providing consistent blood tissue contrast and high signal-to-noise ratio (SNR) in measurements of cardiac function, as well as low coefficients of variation (CoV) for ejection fraction (CoVintra-observer: 2%, CoVinter-observer: 3.8%) and infarct size (CoVintra-observer: 8.4%, CoVinter-observer: 3.8%), despite drastic animal growth.

CONCLUSIONS

Best results are achieved via manual segmentation. We define state-of-the-art procedures for large animal studies at 7 T.

Left ventricular dyssynchrony measured by cardiovascular magnetic resonance-feature tracking in anterior ST-elevation myocardial infarction: relationship with microvascular occlusion myocardial damage

Objectives

Cardiovascular magnetic resonance-feature tracking (CMR-FT) enables quantification of myocardial deformation and may be used as an objective measure of myocardial involvement in ST-elevation myocardial infarction (STEMI). We sought to investigate the associations between myocardial dyssynchrony parameters and myocardium damage for STEMI.

Methods

We analyzed 65 patients (45-80 years old) with anterior STEMI after primary percutaneous coronary intervention during 3-7 days [observational (STEMI) group] and 60 healthy volunteers [normal control (NC) group]. Myocardial dyssynchrony parameters were derived, including global and regional strain, radial rebound stretch and displacement, systolic septal time delay, and circumferential stretch.

Results

CMR characteristics, including morphologic parameters such as left ventricular ejection fraction (LVEF) (45.3% ± 8.2%) and myocardium damage in late gadolinium enhancement (LGE) (19.4% ± 4.7% LV), were assessed in the observation group. The global radial strain (GRS) and global longitudinal strain (GLS) substantially decreased in anterior STEMI compared with the NC group (GRS: 19.4% ± 5.1% vs. 24.8% ± 4.0%, P < 0.05; GLS: -10.1% ± 1.7% vs. -13.7% ± 1.0%, P < 0.05). Among 362 infarcted segments, radial and circumferential peak strains of the infarcted zone were the lowest (14.4% ± 3.2% and -10.7% ± 1.6%, respectively). The radial peak displacement of the infarct zone significantly decreased (2.6 ± 0.4 mm) (P < 0.001) and manifested in the circumferential displacement (3.5° ± 0.7°) in the STEMI group (P < 0.01). As microvascular occlusion (MVO) was additionally present, some strain parameters were significantly impaired in LGE+/MVO+ segments (radial strain [RS]: 12.2% ± 2.1%, circumferential strain [CS]: -9.6% ± 0.7%, longitudinal strain [LS]: -6.8% ± 1.0%) compared to LGE+/MVO- (RS: 14.6% ± 3.2%, CS: -10.8% ± 1.8%, LS: -9.2% ± 1.3%) (P < 0.05). When the extent of transmural myocardial infarction is greater than 75%, the parameter of the systolic septal delay (mean, 148 ms) was significantly reduced compared to fewer degrees of infarction (P < 0.01).

Conclusion

In anterior STEMI, the infarcted septum swings in a bimodal mode, and myocardial injury reduces the radial strain contractility. A more than 75% transmural degree was the septal strain-contraction reserve cut-off point.

Sex differences in cardiac remodeling post myocardial infarction with acute cigarette smoking

Background

Whether cigarette smoking affects the heart post-myocardial infarction (MI) in a sex-dependent way remains controversial. Using a mouse model, we investigated cardiac remodeling under the influence of acute cigarette smoke (CS) exposure following ischemic injury in both sexes.

Methods

Ten cigarettes were smoked twice daily for 2 weeks followed by MI and then 1 additional week post permanent LAD ligation. Cardiac function, histology, and infarct size were assessed, and inflammatory markers quantified by RT–PCR. Statistical comparisons were performed using an unpaired t test or ANOVA followed by Tukey post hoc test.

Results

We observed that cigarette smoking exacerbated both left and right ventricular remodeling only in males at an early stage of post-MI. Females did not display a significant structural and/or functional alteration within 7 days of cardiac remodeling post-MI upon CS exposure. Worsened right ventricular remodeling in males was independent of pulmonary congestion. CS-exposed males exhibited enhanced increases in left ventricular end systolic and diastolic volumes, as well as reductions in ejection fraction and fractional area changes of left ventricular base. At day 7, infarct size was increased by cigarette smoking in males only, which was accompanied by enhanced collagen deposition in both the infarcted and peri-infarcted areas. Both IL-6 and TNF-α mRNA expression significantly increased in CS-exposed MI male group only at day 7 post-MI suggestive of prolonged inflammation.

Conclusions

These findings indicate that CS exposure worsens the progression of cardiac remodeling post-MI in male sex in a significant manner compared to female sex at least at early stages.

Necropsy Validation of a Novel Method for Left Ventricular Mass Quantification in Porcine Transthoracic and Transdiaphragmal Echocardiography

Introduction

Increased left ventricular mass (LVM) is one of the most powerful predictors of adverse cardiovascular events. Clinical evaluation requires reliable, accurate and reproducible echocardiographic LVM-quantification to manage patients. For this purpose, we have developed a novel two-dimensional (2D) method based on adding the mean wall thickness to the left ventricular volume acquired by the biplane method of disks, which has recently been validated in humans using cardiac magnetic resonance as reference value. We assessed the hypothesis that the novel method has better accuracy than conventional one-dimensional (1D) methods, when compared to necropsy LVM in pigs.

Materials and Methods

Echocardiography was performed during anesthesia in 34 Danish Landrace pigs, weight 47–59 kg. All pigs were euthanized, cardiac necropsy was performed and the left ventricle was trimmed and weighed for necropsy LVM. Trans-thoracic echocardiography was applied for parasternal images. Transdiaphragmal echocardiography was applied for the apical images, which are otherwise difficult to obtain in pigs. We compared the conventional 1D- and 2D-methods and the novel 2D-method to the LVM from cardiac necropsy.

Results

Necropsy LVM was 132 ± 11 g (mean ± SD). The novel method had better accuracy than other methods (mean difference ± 95% limits of agreement; coefficients of variation; standard error of the estimate, Pearson's correlation). Novel (−1 ± 20 g; 8%; 11 g; r = 0.70), Devereux (+26 ± 37 g; 15%; 33 g; r = 0.52), Area-Length (+27 ± 34 g; 13 %; 33 g; r = 0.63), Truncated Ellipsoid (+10 ± 30 g; 12%; 19 g; r = 0.63), biplane endo-/epicardial tracing (−3 ± 2 g; 10%; 14 g; r = 0.57). No proportional bias in linear regression was detected for any method, when compared to necropsy LVM.

Conclusion

We confirm high accuracy of the novel 2D-based method compared to conventional 1D/2D-methods.

Anterior STEMI associated with decreased strain in remote cardiac myocardium

To assess (1) global longitudinal strain (GLS) by feature tracking cardiac magnetic resonance (CMR) in the sub-acute and chronic phases after ST-elevation infarction (STEMI) and compare to GLS in healthy controls, and (2) the evolution of GLS and regional longitudinal strain (RLS) over time, and their relationship to infarct location and size. Seventy-seven patients from the CHILL-MI-trial (NCT01379261) who underwent CMR 2–6 days and 6 months after STEMI and 27 healthy controls were included for comparison. Steady state free precession (SSFP) long-axis cine images were obtained for GLS and RLS, and late gadolinium enhancement (LGE) images were obtained for infarct size quantifications. GLS was impaired in the sub-acute (− 11.8 ± 3.0%) and chronic phases (− 14.3 ± 2.9%) compared to normal GLS in controls (− 18.4 ± 2.4%; p < 0.001 for both). GLS improved from sub-acute to chronic phase (p < 0.001). GLS was to some extent determined by infarct size (sub-acute: r² = 0.2; chronic: r² = 0.2, p < 0.001). RLS was impaired in all 6 wall-regions in LAD infarctions in both the sub-acute and chronic phase, while LCx and RCA infarctions had preserved RLS in remote myocardium at both time points. Global longitudinal strain is impaired sub-acutely after STEMI and improvement is seen in the chronic phase, although not reaching normal levels. Global longitudinal strain is only moderately determined by infarct size. Regional longitudinal strain is most impaired in the infarcted region, and LAD infarctions have effects on the whole heart. This could explain why LAD infarcts are more serious than the other culprit vessel infarctions and more often cause heart failure.

Acute phase segmental radial strain correlates with recovery and late gadolinium extent in ST-elevation myocardial infarction (STEMI): analysis of the abciximab intracoronary versus intravenously drug application in STEMI substudy

Background

The role of regional strain evaluation in patients with acute reperfused ST-elevation myocardial infarction (STEMI) is not well determined. The objective of this study was the description of regional strain characteristics in the acute and chronic phase of myocardial infarction and its correlation with symptom-to-balloon time and final extent of myocardial scar assessed by cardiac magnetic resonance imaging.

Methods

The study cohort has been derived from the randomized controlled Abciximab Intracoronary versus Intravenously Drug Application in STEMI (AIDA STEMI) trial enrolled at the University of Ulm. All patients received comprehensive cardiac magnetic resonance imaging examinations in the acute phase and 6 months later.

Results

There was a significant improvement of all global deformation indices over time (global longitudinal strain: -13.1%±5.1% to -15.5%±5.8%, P=0.001; global circumferential strain: -14.4%±3.7% to -16.8%±3.6%, P<0.0001; global radial strain: 28.1%±8.7% to 31.9%±9.2%, P=0.0002). Mean radial strain of ischemic segments significantly improved (16.6%±10.8% to 23.7%±12.8%, P<0.0001), while mean radial strain of remote segments remained unchanged (40.2%±9.4% to 39.4%±9.4%, P=0.570). There was a significant correlation between acute phase radial strain of ischemic segments and either symptom-to-balloon time (P=0.013), as well as extent of late gadolinium enhancement at follow-up (P<0.0001). Using a cut-off of ≤27%, acute phase radial strain predicted infarction of the corresponding segment with high sensitivity and specificity (74.4% and 69.0% respectively, P<0.001).

Conclusions

Segmental radial strain in the acute phase of infarction showed a significant correlation to either symptom-to-balloon-time and the extent of late gadolinium enhancement at follow-up, thus potentially serving as early surrogate for left ventricular remodeling and outcome in STEMI.

Injectable Myocardial Matrix Hydrogel Mitigates Negative Left Ventricular Remodeling in a Chronic Myocardial Infarction Model

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Myocardial matrix hydrogel preserves LV volumes and apical wall thickening in a chronic MI model.

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Myocardial matrix hydrogel trends toward reduced fibrosis.

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In vivo differential gene expression analysis shows the matrix modulates cardiac muscle contraction, metabolism, fibrosis, and the inflammatory/immune response in a chronic MI model.

A first-in-man clinical study on a myocardial-derived decellularized extracellular matrix hydrogel suggested the potential for efficacy in chronic myocardial infarction (MI) patients. However, little is understood about the mechanism of action in chronic MI. In this study, the authors investigated the efficacy and mechanism by which the myocardial matrix hydrogel can mitigate negative left ventricular (LV) remodeling in a rat chronic MI model. Assessment of cardiac function via magnetic resonance imaging demonstrated preservation of LV volumes and apical wall thickening. Differential gene expression analyses showed the matrix is able to prevent further negative LV remodeling in the chronic MI model through modulation of the immune response, down-regulation of pathways involved in heart failure progression and fibrosis, and up-regulation of genes important for cardiac muscle contraction.

Evolution of left ventricular function among subjects with ST-elevation myocardial infarction after percutaneous coronary intervention

Background

Atrioventricular plane displacement (AVPD) reflects longitudinal left ventricular (LV) systolic function, and wall thickening (WT) regional radial LV function. The temporal evolution of these measures after STEMI with CMR has not been evaluated. We aimed to investigate how AVPD and WT are affected globally and regionally from the sub-acute to the chronic phase after ST-elevation myocardial infarction (STEMI).

Methods

Healthy volunteers without cardiovascular disease and medication (controls, n = 20) and patients from the CHILL-MI study (NCT01379261) prospectively underwent magnetic resonance imaging (MRI) 2–6 days and 6 months after STEMI (n = 77). CHILL-MI randomized STEMI-patients to cooling therapy initiated before reperfusion or standard of care. AVPD was measured at six points in three long axis cine images and wall thickening in short axis cine images. Infarction was quantified using late gadolinium enhancement (LGE) and used to define infarct and remote segments.

Results

There were no difference in AVPD either at acute or chronic phase (p = 0.90 and p = 0.40) or WT (p = 0.85 and p = 0.99) between patients randomized to cooling therapy and standard of care. Therefore, the results are presented for the pooled cohort. Global AVPD was decreased in both the sub-acute (12 ± 2 mm, p < 0.001) and the chronic phase (13 ± 2 mm, p < 0.001) compared to controls (15 ± 2 mm) with a partial recovery of AVPD (p < 0.001) in the chronic phase. Patients with left anterior descending (LAD) and right coronary artery (RCA) infarcts had decreased AVPD in the chronic phase in both infarcted and remote segments. Mean WT was decreased in patients with LAD infarction both in the sub-acute and the chronic phase in both infarcted and remote segments. The decrease in WT in patients with RCA and left circumflex (LCx) infarcts was more affected in the infarcted segments, especially in the chronic phase.

Conclusion

AVPD was a global rather than regional marker of cardiac function in this STEMI study and this may explain the prognostic importance of local measurements of mitral annular plane systolic excursion (MAPSE). The decrease in WT in remote myocardium even in the chronic phase needs to be taken into consideration when combining functional measurements with infarct quantification for diagnosis of post-ischemic stunning and hibernation.