Value of segmental myocardial strain by 2-dimensional strain echocardiography for assessment of scar area induced in a rat model of myocardial infarction

Research Progress of Myocardial Fibrosis and Atrial Fibrillation

With the aging population and the increasing incidence of basic illnesses such as hypertension and diabetes (DM), the incidence of atrial fibrillation (AF) has increased significantly. AF is the most common arrhythmia in clinical practice, which can cause heart failure (HF) and ischemic stroke (IS), increasing disability and mortality. Current studies point out that myocardial fibrosis (MF) is one of the most critical substrates for the occurrence and maintenance of AF. Although myocardial biopsy is the gold standard for evaluating MF, it is rarely used in clinical practice because it is an invasive procedure. In addition, serological indicators and imaging methods have also been used to evaluate MF. Nevertheless, the accuracy of serological markers in evaluating MF is controversial. This review focuses on the pathogenesis of MF, serological evaluation, imaging evaluation, and anti-fibrosis treatment to discuss the existing problems and provide new ideas for MF and AF evaluation and treatment.

Investigation of Left Ventricular Strain and Its Morphological Basis During Different Stages of Diastolic and Systolic Dysfunction in Spontaneously Hypertensive Rat

BACKGROUND

Myocardial fibrosis plays an important role in the pathogenesis of hypertensive cardiac dysfunction, and myocardial strain could detect early systolic abnormalities when left ventricular ejection fraction (LVEF) is preserved. The aim of this study was to investigate the characteristics of left ventricular multidirectional strain during different stages of heart dysfunction and the possible morphological basis in spontaneously hypertensive rats (SHRs).

METHODS

SHRs and Wistar-Kyoto (WKY) rats were randomly divided into cages and observed for 3-25 months. Echocardiographic measurements, LV + dp/dtmax and left ventricular end-diastolic pressure (LVEDP), and histological collagen volume fraction (CVF) were observed in all rats.

RESULTS

According to LVEF and LVEDP, SHRs were divided into normal cardiac function group (group A), diastolic dysfunction group (group B1), and systolic dysfunction group (group B2). In group A, myocardial strain and CVF showed no difference compared with the control group. In group B1, global longitudinal strain (GLS) and endocardial longitudinal strain (SL-endo) were lower than those in group A CVF-endo was increased (all P < 0.05). In group B2, global and layer-specific strain decreased significantly, along with the increased CVF-endo and CVF-epi (all P < 0.05). The decrease of GLS and SL-endo was moderately correlated with the increase of CVF-endo. The reduction of LVEF was correlated with the decrease of SC-endo (r = 0.65, P < 0.01).

CONCLUSIONS

Pathological myocardial fibrosis associated with hypertension develops from the inner to outer layer of myocardium, which is coincident with the impairment of myocardial deformation, where longitudinal strain is involved firstly and LVEF declines when all directions of strain are reduced.

Novel Approaches in Cardiac Imaging for Non-invasive Assessment of Left Heart Myocardial Fibrosis

In the past, the identification of myocardial fibrosis was only possible through invasive histologic assessment. Although endomyocardial biopsy remains the gold standard, recent advances in cardiac imaging techniques have enabled non-invasive tissue characterization of the myocardium, which has also provided valuable insights into specific disease processes. The diagnostic accuracy, incremental yield and prognostic value of speckle tracking echocardiography, late gadolinium enhancement and parametric mapping modules by cardiac magnetic resonance and cardiac computed tomography have been validated against tissue samples and tested in broad patient populations, overall providing relevant clinical information to the cardiologist. This review describes the patterns of left ventricular and left atrial fibrosis, and their characterization by advanced echocardiography, cardiac magnetic resonance and cardiac computed tomography, allowing for clinical applications in sudden cardiac death and management of atrial fibrillation.

Comparison of global and regional myocardial strains in patients with heart failure with a preserved ejection fraction vs hypertension vs age-matched control

Background

With an increasing clinical importance of the treatment of the heart failure (HF) with preserved ejection fraction (HFpEF), it is important to be certain of the diagnosis of HF. We investigated global and regional left ventricular (LV) strains using speckle tracking echocardiography (STE) in patients with HFpEF and compared those parameters with that of patients with hypertension and normal subjects.

Methods

Peak longitudinal, circumferential and radial strains were assessed globally and regionally for each study groups using STE. Diastolic strain rate was also determined.

Results

There were 50 patients in HFpEF group, 56 patients in hypertension group and 46 age-matched normal subjects. In patients with HFpEF, global peak longitudinal, circumferential and radial strain and strain rate were reduced compared to both hypertension patients and normal controls (− 15.5 ± 5.3 vs − 17.7 ± 3.1 and − 19.9 ± 2.0; − 9.7 ± 2.2 vs − 19.3 ± 3.1 and − 20.5 ± 3.3; 17.7 ± 8.2 vs 38.4 ± 12.4 and 43.6 ± 11.9, respectively, P <  0.001, for all). The diagnostic performance of global circumferential strain to predict the HFpEF was greatest among strain parameters (area under the curve = 0.997).

Conclusions

In the speckle tracking echocardiography, impaired peak global strain and homogeneously reduced regional strain was observed in HFpEF patients compared to the hypertension patients and normal subjects in decreasing order. This can provide early information on the initiation of LV deformation of HFpEF in patients with hypertension or normal subjects.

In vivo assessment of regional mechanics post-myocardial infarction: A focus on the road ahead

Cardiovascular disease, particularly the occurrence of myocardial infarction (MI), remains a leading cause of morbidity and mortality (Go et al., Circulation 127: e6-e245, 2013; Go et al. Circulation 129: e28-e292, 2014). There is growing recognition that a key factor for post-MI outcomes is adverse remodeling and changes in the regional structure, composition, and mechanical properties of the MI region itself. However, in vivo assessment of regional mechanics post-MI can be confounded by the species, temporal aspects of MI healing, as well as size, location, and extent of infarction across myocardial wall. Moreover, MI regional mechanics have been assessed over varying phases of the cardiac cycle, and thus, uniform conclusions regarding the material properties of the MI region can be difficult. This review assesses past studies that have performed in vivo measures of MI mechanics and attempts to provide coalescence on key points from these studies, as well as offer potential recommendations for unifying approaches in terms of regional post-MI mechanics. A uniform approach to biophysical measures of import will allow comparisons across studies, as well as provide a basis for potential therapeutic markers.

Echocardiographic assessment of myocardial infarction: comparison of a rat model in two strains

The purpose of this study was to induce myocardial infarction (MI) and compare the echocardiographic parameters and mortality ratio of Lewis inbred and Wistar outbred strain before and after the procedure to help choose the best one for MI studies. In this study MI was induced in 46 Lewis and 34 Wistar by occlusion of left anterior descending artery (LAD). Doppler, two-dimensional (2-D) and 2-D guided M-mode images were recorded from parasternal long-axis and parasternal short-axis and apical four-chamber views. The following parameters were acquired. Interventricular septum diastolic and systolic dimension (IVSd, s), diastolic and systolic left ventricular internal diameter (LVIDd, s), diastolic and systolic left ventricular posterior wall dimension (LVPWd, s), ejection fraction (EF), and fractional shortening (FS). The significant changes were observed in systolic IVS, LVID and EF and FS before and after MI and no significant difference was detected between Lewis and Wistar. The high mortality rate of 51% was seen in the procedure, including anesthesia in Lewis compared to 34% in Wistar. As a conclusion the echocardiographic parameters of these two strains were similar, but according to mortality rate and more cardiac anatomic variation in Lewis rats, Wistar is better for MI studies.

The cardioprotective efficacy of TVP1022 against ischemia/reperfusion injury and cardiac remodeling in rats

Following acute myocardial infarction (MI), early and successful reperfusion is the most effective strategy for reducing infarct size and improving the clinical outcome. However, immediate restoration of blood flow to the ischemic zone results in myocardial damage, defined as “reperfusion‐injury”. Whereas we previously reported that TVP1022 (the S‐isomer of rasagiline, FDA‐approved anti‐Parkinson drug) decreased infarct size 24 h post ischemia reperfusion (I/R) in rats, in this study we investigated the chronic cardioprotective efficacy of TVP1022 14 days post‐I/R. To simulate the clinical settings of acute MI followed by reperfusion therapy, we employed a rat model of left anterior descending artery occlusion for 30 min followed by reperfusion and a follow‐up for 14 days. TVP1022 was initially administered postocclusion–prereperfusion, followed by chronic daily administrations. Cardiac performance and remodeling were evaluated using customary and advanced echocardiographic methods, hemodynamic measurements by Millar Mikro‐Tip^® catheter, and histopathological techniques. TVP1022 administration markedly decreased the remodeling process as illustrated by attenuation of left ventricular enlargement and cardiac hypertrophy (both at the whole heart and the cellular level). Furthermore, TVP1022 inhibited cardiac fibrosis and reduced ventricular BNP levels. Functionally, TVP1022 treatment preserved cardiac wall motion. Specifically, the echocardiographic and most of the direct hemodynamic measures were pronouncedly improved by TVP1022. Collectively, these findings indicate that TVP1022 provides prominent cardioprotection against I/R injury and post‐MI remodeling in this I/R model.

New Echocardiographic Protocol for the Assessment of Experimental Myocardial Infarction in Rats

BACKGROUND

The rat infarct model was used extensively to study the pathophysiology of myocardial infarction and to evaluate different therapies. Transthoracic echocardiography is used in rats in order to assess cardiac anatomy and function, being a safe and reliable non-invasive technique. However, studies combining conventional with new echo techniques, such as tissue Doppler imaging (TDI) and speckletracking echocardiography (STE), are lacking.

OBJECTIVES

To validate a protocol using the available conventional and new echocardiographic techniques (TDI and STE) for a comprehensive assessment of cardiac remodelling and function, after myocardial infarction in rats.

METHODS

Ten Wistar (W) and five Sprague Dawley (SD) male rats (aged 21±2 weeks, mean weight 355±43 g) were evaluated by echocardiography, before and 24 hours post-ligation of the left coronary artery, with previous anaesthesia. Left ventricular (LV) structure was assessed by end-diastolic and endsystolic anterior wall thickness and LV diameters (from the SAX view), while LV function by fractional shortening (FS) and ejection fraction (EF) (by area-length formula), septal mitral annular plane systolic excursion (MAPSE), cardiac output (CO), myocardial performance index (MPI), septal mitral annular systolic velocity (S', by TDI), and global circumferential and radial systolic strain (GCS, GRS) and strain rate (GCSr, GRSr) by STE, from the SAX view at the level of papillary muscles.

RESULTS

Feasibility of measuring the above mentioned parameters was 100%. Twenty-four hours after myocardial infarction, rats had lower heart rate (373±44 vs. 351±32 bpm, p<0.05) and thinner LV anterior wall, while LV diameters and volumes were significantly higher. FS (54±7 vs. 33±9%), EF (72±9vs. 47±10%), septal MAPSE (2.02±0.17 vs. 1.44±0.22 mm), CO (76±15 vs. 48±12 ml/min), MPI (0.33±0.11 vs. 0.50±0.14), S' (5.58±1.20 vs. 3.84±1.06 cm/s), and LV strain and strain rate (GCS: -23.52±2.44 vs. -13.33±1.51% and GRS: 50.45±13.11 vs. 17.27±5.2%, GCSr: -8.42±0.85 vs. -4.68±0.53; and GRSr: 11.93±2.39 vs. 4.89±1.18 1/s) were significantly lower, all p<0.01.

CONCLUSIONS

Our echocardiographic protocol of experimental myocardial infarction in rats is feasible. The impact of myocardial infarction in rats could be more extensively assessed using a comprehensive echocardiographic protocol of conventional and specific myocardial parameters, measured by TDI and STE, in order to quantify better the LV structure and function. Therefore, we suggest that this protocol may be used in order to assess the effect of different regenerative therapies in experimental myocardial infarction in rats.

Ultrasound bio-microscopy for measurement of coronary artery flow and estimation of infarct size in a mouse model of acute myocardial infarction

Ultrasound bio-microscopy was used to measure hemodynamic changes in the left main coronary artery after myocardial infarction (MI), and its usefulness in estimating infarct size was evaluated. MI was induced by left anterior descending artery ligation. Diastolic peak velocity (Vd), mean flow velocity (Vmean) and the velocity-time integral (VTI) were measured 2 and 6 h after MI. Serum troponin I levels were assayed 2, 6 and 12 h after MI. At 2 h, Vmean and VTI significantly differed between mice that underwent low and high left anterior descending artery ligation; Vd, Vmean and VTI were correlated with infarct size (r = -0.557, -0.693 and -0.672, respectively; all p < 0.01). Infarct size was more strongly correlated with 2-h ultrasound bio-microscopy measurements than with 2-h serum troponin I level. Measurement of coronary artery blood flow by ultrasound bio-microscopy may be useful for early estimation of infarct size in mice.