Myocardial tissue characterization and aortic stenosis

A non-contrast CMR index for assessing myocardial fibrosis

PURPOSE

Safe, sensitive, and non-invasive imaging methods to assess the presence, extent, and turnover of myocardial fibrosis are needed for early stratification of risk in patients who might develop heart failure after myocardial infarction. We describe a non-contrast cardiac magnetic resonance (CMR) approach for sensitive detection of myocardial fibrosis using a canine model of myocardial infarction and reperfusion.

METHODS

Seven dogs had coronary thrombotic occlusion of the left anterior descending coronary arteries followed by fibrinolytic reperfusion. CMR studies were performed at 7days after reperfusion. A CMR spin-locking T₁ρ mapping sequence was used to acquire T₁ρ dispersion data with spin-lock frequencies of 0 and 511Hz. A fibrosis index map was derived on a pixel-by-pixel basis. CMR native T₁ mapping, first-pass myocardial perfusion imaging, and post-contrast late gadolinium enhancement imaging were also performed for assessing myocardial ischemia and fibrosis. Hearts were dissected after CMR for histopathological staining and two myocardial tissue segments from the septal regions of adjacent left ventricular slices were qualitatively assessed to grade the extent of myocardial fibrosis.

RESULTS

Histopathology of 14 myocardial tissue segments from septal regions was graded as grade 1 (fibrosis area, <20% of a low power field, n=9), grade 2 (fibrosis area, 20-50% of field, n=4), or grade 3 (fibrosis area, >50% of field, n=1). A dramatic difference in fibrosis index (183%, P<0.001) was observed by CMR from grade 1 to 2, whereas differences were much smaller for T₁ρ (9%, P=0.14), native T₁ (5.5%, P=0.12), and perfusion (-21%, P=0.05).

CONCLUSION

A non-contrast CMR index based on T₁ρ dispersion contrast was shown in preliminary studies to detect and correlate with the extent of myocardial fibrosis identified histopathologically. A non-contrast approach may have important implications for managing cardiac patients with heart failure, particularly in the presence of impaired renal function.

Micro-RNA-21 (biomarker) and global longitudinal strain (functional marker) in detection of myocardial fibrotic burden in severe aortic valve stenosis: a pilot study

Aims

Myocardial fibrosis (MF) is a deleterious consequence of aortic valve stenosis (AVS). Global longitudinal strain (GLS) is a novel left ventricular (LV) functional parameter potentially useful to non-invasively estimate MF. MicroRNAs (miRNAs) are non-coding small ribonucleic acids (RNA) modulating genes function, mainly through RNA degradation. miRNA-21 is a biomarker associated with MF in pressure overload. The aim of the present study was to find an integrated algorithm for detection of MF using a combined approach with both bio- and functional markers.

Methods

Thirty-six patients (75.2 ± 8 y.o.; 63 % Female) with severe AVS and preserved LV ejection fraction (EF), candidate to surgical aortic valve replacement (sAVR) were enrolled. Clinical, bio-humoral evaluation (including plasmatic miRNA-21 collected using specific tubes, PAXgene, for stabilization of peripheral RNA) and a complete echocardiographic study, including GLS and septal strain, were performed before sAVR. Twenty-eight of those patients underwent sAVR and, in 23 of them, an inter-ventricular septum biopsy was performed. Tissues were fixed in formalin and embedded in paraffin. Sections were stained with Hematoxylin and Eosin for histological evaluation and with histochemical Masson trichrome for collagen fibers. The different components were calculated and expressed as micrometers². To evaluate tissue miRNA components, sections 2-μm thick were cut using a microtome blade for each slide. Regression analysis was performed to test association between dependent variable and various predictors included in the model.

Results

Despite a preserved EF (66 ± 11 %), patients presented altered myocardial deformation parameters (GLS −14,02 ± 3.8 %; septal longitudinal strain, SSL −9.63 ± 2.9 %; septal longitudinal strain rate, SL-Sr −0.58 ± 0.17 1/s; Septal Longitudinal early-diastolic strain rate, SL-SrE 0.62 ± 0.32 1/s). The extent of MF showed an inverse association with both GLS and septal longitudinal deformation indices (GLS: R² = 0.30; p = 0.02; SSL: R² = 0.36; p = 0.01; SL-Sr: R² = 0.39; p < 0.001; SL-SrE: R² = 0.35; p = 0.001). miRNA-21 was mainly expressed in fibrous tissue (p < 0.0001). A significant association between MF and plasmatic miRNA-21, alone and weighted for measures of structural (LVMi R² = 0.50; p = 0.0005) and functional (SSL R² = 0.35; p = 0.006) remodeling, was found.

Conclusions

In AVS, MF is associated with alterations of regional and global strain. Plasmatic miRNA-21 is directly related to MF and associated with LV structural and functional impairment.

New echocardiographic techniques in the evaluation of left ventricular function in obesity

OBJECTIVE

Obesity has reached global epidemic proportions and is associated with numerous comorbidities, including major cardiovascular (CV) diseases.

DESIGN AND METHODS

It has many adverse effects on hemodynamics and CV structure and function: it increases total blood volume and cardiac output, and the cardiac workload is greater. Typically, obese patients have a higher cardiac output but a lower level of total peripheral resistance at any given level of arterial pressure. Most of the increase in cardiac output in obesity is caused by stroke volume, although heart rate typically mildly increases also due to enhanced sympathetic activation.

RESULTS

Over the last few years, experimental investigations have unraveled some important pathogenetic mechanisms that may underlie a specific form of "obesity cardiomyopathy." Bariatric surgery represents an effective alternative to treat obesity when nonsurgical weight loss programs (diet + behavior modifications + regular exercise) have failed. A great numbers of questions are still open in the global comprehension of the pathophysiological interactions between obesity and heart.

CONCLUSION

Conventional two-dimensional Doppler echocardiography, integrated by relative new technological ultrasonic approaches, represents the reference technique to study and possibly clarify both the very complex hemodynamic changes induced by obesity and those relative to obesity treatment.