Transesophageal echocardiography in swine: evaluation of left and right ventricular structure, function and myocardial work

Cardioprotection in cardiovascular surgery

Since the invention of cardiopulmonary bypass, cardioprotective strategies have been investigated to mitigate ischemic injury to the heart during aortic cross-clamping and reperfusion injury with cross-clamp release. With advances in cardiac surgical and percutaneous techniques and post-operative management strategies including mechanical circulatory support, cardiac surgeons are able to operate on more complex patients. Therefore, there is a growing need for improved cardioprotective strategies to optimize outcomes in these patients. This review provides an overview of the basic principles of cardioprotection in the setting of cardiac surgery, including mechanisms of cardiac injury in the context of cardiopulmonary bypass, followed by a discussion of the specific approaches to optimizing cardioprotection in cardiac surgery, including refinements in cardiopulmonary bypass and cardioplegia, ischemic conditioning, use of specific anesthetic and pharmaceutical agents, and novel mechanical circulatory support technologies. Finally, translational strategies that investigate cardioprotection in the setting of cardiac surgery will be reviewed, with a focus on promising research in the areas of cell-based and gene therapy. Advances in this area will help cardiologists and cardiac surgeons mitigate myocardial ischemic injury, improve functional post-operative recovery, and optimize clinical outcomes in patients undergoing cardiac surgery.

Beyond conduction impairment: Unveiling the profound myocardial injury in left bundle branch block

BACKGROUND

Left bundle branch block (LBBB) represents a frequently encountered conduction system disorder. Despite its widespread occurrence, a continual dilemma persists regarding its intricate association with underlying cardiomyopathy and its pivotal role in the initiation of dilated cardiomyopathy. The pathologic alterations linked to LBBB-induced cardiomyopathy (LBBB-CM) have remained elusive.

OBJECTIVE

This study sought to investigate the chronologic dynamics of LBBB to left ventricular dysfunction and the pathologic mechanism of LBBB-CM.

METHODS

LBBB model was established through main left bundle branch trunk ablation in 14 canines. All LBBB dogs underwent transesophageal echocardiography and electrocardiography before ablation and at 1 month, 3 months, 6 months, and 12 months after LBBB induction. Single-photon emission computed tomography imaging was performed at 12 months. We then harvested the heart from all LBBB dogs and 14 healthy adult dogs as normal controls for anatomic observation, Purkinje fiber staining, histologic staining, and connexin43 protein expression quantitation.

RESULTS

LBBB induction caused significant fibrotic changes in the endocardium and mid-myocardium. Purkinje fibers exhibited fatty degeneration, vacuolization, and fibrosis along with downregulated connexin43 protein expression. During a 12-month follow-up, left ventricular dysfunction progressively worsened, peaking at the end of the observation period. The association between myocardial dysfunction, hypoperfusion, and fibrosis was observed in the LBBB-afflicted canines.

CONCLUSION

LBBB may lead to profound myocardial injury beyond its conduction impairment effects. The temporal progression of left ventricular dysfunction and the pathologic alterations observed shed light on the complex relationship between LBBB and cardiomyopathy. These findings offer insights into potential mechanisms and clinical implications of LBBB-CM.

Intensified training augments cardiac function, but not blood volume, in male youth elite ice hockey team players

While it is well-established that a period of interval training performed at near maximal effort, such as speed endurance training (SET), enhances intense exercise performance in well-trained individuals, less is known about its effect on cardiac morphology and function as well as blood volume. To investigate this, we subjected 12 Under-20 Danish national team ice hockey players (age 18 ± 1 years, mean ± SD) to 4 weeks of SET, consisting of 6-10 × 20 s skating bouts at maximal effort interspersed by 2 min of recovery conducted three times weekly. This was followed by 4 weeks of regular training (follow-up). We assessed resting cardiac function and dimensions using transthoracic echocardiography and quantified total blood volume with the carbon monoxide rebreathing technique at three time points: before SET, after SET and after the follow-up period. After SET, stroke volume had increased by 10 (2-18) mL (mean (95% CI)), left atrial end-diastolic volume by 10 (3-17) mL, and circumferential strain improved by 0.9%-points (1.7-0.1) (all P < 0.05). At follow-up, circumferential strain and left atrial end-diastolic volume were reverted to baseline levels, while stroke volume remained elevated. Blood volume and morphological parameters for the left ventricle, including mass and end-diastolic volume, did not change during the study. In conclusion, our findings demonstrate that a brief period of SET elicits beneficial central cardiac adaptations in elite ice hockey players independent of changes in blood volume.

Pigs as Models to Test Cardiovascular Devices

Pigs as laboratory animals are used in preclinical studies aimed at developing medical devices for cardiac surgery. The anatomy of the cardiovascular system of these animals has been well studied and acknowledged as suitable for use and the testing of new cardiovascular devices developed for humans. However, there are no morphometric characteristics of the aortic root and thoraco-abdominal part of porcine aorta. This can lead to difficulties in experimental surgery and even result in the death of experimental animals due to the mismatch in the size of the implantable devices. Thus, such information is essential to enhance the efficiency of surgical technologies used for eliminating aortic pathologies in their various sections. The purpose of our research is to study the anatomy of the aorta in mini pigs and to assess whether the size, age, and sex of the animals affect the size of the main structures in their aortas. In addition, we attempted to compare the results obtained by transesophageal echocardiography (TEE) and angiography. We studied 28 laboratory mini pigs, dividing them into three groups by body weight (40-70 kg, 71-90 kg, and 90 kg). We did not find any relationship between the external somatometric characteristics of the animals and the size of their aortas. Animals have individual anatomical variability in their cardiovascular systems, which means that they need to be examined in terms of preoperative planning by any available method-echocardiography, angiography, or multispiral computed tomography (CT).

Association between speckle tracking echocardiography and pressure-volume loops during cardiogenic shock development

BACKGROUND

The relationship between speckle tracking assessed global longitudinal strain (GLS) and Doppler-based echocardiography with basic physiological markers of cardiac function derived from pressure-volume loops is poorly elucidated.

OBJECTIVE

We aimed to describe the association between LS and Doppler-based echocardiography and direct measurements of central haemodynamic parameters from conductance catheter-based pressure-volume loops in an animal model with increasing left ventricular (LV) dysfunction.

METHODS

12 Danish landrace female pigs (75-80 kg) were used. All instrumentations were performed percutaneously, including the conductance catheter in the LV. Progressive LV dysfunction was induced by embolisation through the left main coronary artery with microspheres every 3 min until a >50% reduction in cardiac output (CO) or mixed venous saturation (SvO2), compared with baseline, or SvO2 <30%. Echocardiography was performed at baseline and 90 s after each injection.

RESULTS

With progressive LV dysfunction, mean CO decreased from 5.6±0.9 L/min to 2.1±0.9 L/min, and mean SvO2 deteriorated from 61.1±7.9% to 35.3±6.1%. Mean LS and LV outflow tract velocity time integral (LVOT VTI) declined from -13.8±3.0% to -6.1±2.0% and 16.9±2.6 cm to 7.8±1.8 cm, respectively. LS and LVOT VTI showed the strongest correlation to stroke work in unadjusted linear regression (r2=0.53 and r2=0.49, respectively). LS correlated significantly with stroke volume, end-systolic elastance, systolic blood pressure, ventriculo-arterial coupling and arterial elastance.

CONCLUSION

In an animal model of acute progressive LV dysfunction, echocardiographic and conductance catheter-based measurements changed significantly. LS and LVOT VTI displayed the earliest and the largest alterations with increased myocardial damage and both correlated strongest with stroke work.

The Self-Expandable Impella CP (ECP) as a Mechanical Resuscitation Device

The survival rate of cardiac arrest (CA) can be improved by utilizing percutaneous left ventricular assist devices (pLVADs) instead of conventional chest compressions. However, existing pLVADs require complex fluoroscopy-guided placement along a guidewire and suffer from limited blood flow due to their cross-sectional area. The recently developed self-expandable Impella CP (ECP) pLVAD addresses these limitations by enabling guidewire-free placement and increasing the pump cross-sectional area. This study evaluates the feasibility of resuscitation using the Impella ECP in a swine CA model. Eleven anesthetized pigs (73.8 ± 1.7 kg) underwent electrically induced CA, were left untreated for 5 min and then received pLVAD insertion and activation. Vasopressors were administered and defibrillations were attempted. Five hours after the return of spontaneous circulation (ROSC), the pLVAD was removed, and animals were monitored for an additional hour. Hemodynamics were assessed and myocardial function was evaluated using echocardiography. Successful guidewire-free pLVAD placement was achieved in all animals. Resuscitation was successful in 75% of cases, with 3.5 ± 2.0 defibrillations and 1.8 ± 0.4 mg norepinephrine used per ROSC. Hemodynamics remained stable post-device removal, with no adverse effects or aortic valve damage observed. The Impella ECP facilitated rapid guidewire-free pLVAD placement in fibrillating hearts, enabling successful resuscitation. These findings support a broader clinical adoption of pLVADs, particularly the Impella ECP, for CA.

Crafting a Rigorous, Clinically Relevant Large Animal Model of Chronic Myocardial Ischemia: What Have We Learned in 20 Years?

The past several decades have borne witness to several breakthroughs and paradigm shifts within the field of cardiovascular medicine, but one component that has remained constant throughout this time is the need for accurate animal models for the refinement and elaboration of the hypotheses and therapies crucial to our capacity to combat human disease. Numerous sophisticated and high-throughput molecular strategies have emerged, including rational drug design and the multi-omics approaches that allow extensive characterization of the host response to disease states and their prospective resolutions, but these technologies all require grounding within a faithful representation of their clinical context. Over this period, our lab has exhaustively tested, progressively refined, and extensively contributed to cardiovascular discovery on the basis of one such faithful representation. It is the purpose of this paper to review our porcine model of chronic myocardial ischemia using ameroid constriction and the subsequent myriad of physiological and molecular-biological insights it has allowed our lab to attain and describe. We hope that, by depicting our methods and the insight they have yielded clearly and completely-drawing for this purpose on comprehensive videographic illustration-other research teams will be empowered to carry our work forward, drawing on our experience to refine their own investigations into the pathogenesis and eradication of cardiovascular disease.

Robotic right ventricle is a biohybrid platform that simulates right ventricular function in (patho)physiological conditions and intervention

The increasing recognition of the right ventricle (RV) necessitates the development of RV-focused interventions, devices and testbeds. In this study, we developed a soft robotic model of the right heart that accurately mimics RV biomechanics and hemodynamics, including free wall, septal and valve motion. This model uses a biohybrid approach, combining a chemically treated endocardial scaffold with a soft robotic synthetic myocardium. When connected to a circulatory flow loop, the robotic right ventricle (RRV) replicates real-time hemodynamic changes in healthy and pathological conditions, including volume overload, RV systolic failure and pressure overload. The RRV also mimics clinical markers of RV dysfunction and is validated using an in vivo porcine model. Additionally, the RRV recreates chordae tension, simulating papillary muscle motion, and shows the potential for tricuspid valve repair and replacement in vitro. This work aims to provide a platform for developing tools for research and treatment for RV pathophysiology.

Commotio Cordis in 2023

Since the nationally televised cardiac arrest of American National Football League player Damar Hamlin in January 2023, commotio cordis has come to the forefront of public attention. Commotio cordis is defined as sudden cardiac arrest due to direct trauma to the precordium resulting in ventricular fibrillation or ventricular tachycardia. While the precise incidence of commotio cordis is not known due to a lack of standardized, mandated reporting, it is the third most common cause of sudden cardiac death in young athletes, with more than 75% of cases occurring during organized and recreational sporting events. Given that survival is closely tied to how quickly victims receive cardiopulmonary resuscitation and defibrillation, it is crucial to raise awareness of commotio cordis so that athletic trainers, coaches, team physicians, and emergency medical personnel can rapidly diagnose and treat this often-fatal condition. Broader distribution of automated external defibrillators in sporting facilities as well as increased presence of medical personnel during sporting events would also likely lead to higher survival rates.

Dos and don'ts in large animal models of aortic insufficiency

Aortic insufficiency caused by paravalvular leakage (PVL) is one of the most feared complications following transcatheter aortic valve replacement (TAVI) in patients. Domestic pigs (Sus scrofa domestica) are a popular large animal model to study such conditions and develop novel diagnostic and therapeutic techniques. However, the models based on prosthetic valve implantation are time intensive, costly, and often hamper further hemodynamic measurements such as PV loop and 4D MRI flow by causing implantation-related wall motion abnormalities and degradation of MR image quality. This study describes in detail, the establishment of a minimally invasive porcine model suitable to study the effects of mild-to-moderate “paravalvular“ aortic regurgitation on left ventricular (LV) performance and blood flow patterns, particularly under the influence of altered afterload, preload, inotropic state, and heart rate. Six domestic pigs (Swiss large white, female, 60–70 kg of body weight) were used to establish this model. The defects on the hinge point of aortic leaflets and annulus were created percutaneously by the pierce-and-dilate technique either in the right coronary cusp (RCC) or in the non-coronary cusp (NCC). The hemodynamic changes as well as LV performance were recorded by PV loop measurements, while blood flow patterns were assessed by 4D MRI. LV performance was additionally challenged by pharmaceutically altering cardiac inotropy, chronotropy, and afterload. The presented work aims to elaborate the dos and don'ts in porcine models of aortic insufficiency and intends to steepen the learning curve for researchers planning to use this or similar models by giving valuable insights ranging from animal selection to vascular access choices, placement of PV Loop catheter, improvement of PV loop data acquisition and post-processing and finally the induction of paravalvular regurgitation of the aortic valve by a standardized and reproducible balloon induced defect in a precisely targeted region of the aortic valve.

Assessment of subclinical left ventricle myocardial dysfunction using global myocardial work in type 2 diabetes mellitus patients with preserved left ventricle ejection fraction

BACKGROUND

The purpose of this study was to assess subclinical left ventricle (LV) myocardial dysfunction using global myocardial work (MW) in type 2 diabetes mellitus (T2DM) patients with preserved left ventricle ejection fraction (LVEF).

METHODS

Sixty T2DM patients and 60 normal controls were enrolled in the study. Apical 4-, 3- and 2-chamber views were acquired by two-dimensional echocardiography. Peak systolic myocardial global longitudinal strain (GLS), global myocardial work index (GWI), global constructive work (GCW), global wasted work (GWW), and myocardial work efficiency (GWE) were determined by speckle-tracking echocardiography (STE).

RESULTS

The GLS values in the T2DM patients were significantly lower than those in normal controls (p < 0.001). The GWW in T2DM patients was significantly greater than that in normal controls, while GWI, GCW and GWE was significantly lower (p < 0.001). Receiver operating characteristic (ROC) analysis showed there were no significant different difference between GWW, GWE and GLS in the area under the curves (AUCs). In T2DM patients, fasting plasma glucose was positively correlated with GWW but negatively correlated with GWE, and GLS was negatively correlated with GWI and GCW.

CONCLUSION

From the research, we found that global MW as new technique could detect the subclinical LV myocardial dysfunction and confirm that the impaired LV function in T2DM patients with preserved LV systolic function.

Pathology and Advanced Imaging—Characterization of a Congenital Cardiac Defect and Complex Hemodynamics in a Pig: A Case Report

Domestic pigs are widely used in cardiovascular research as the porcine circulatory system bears a remarkable resemblance to that of humans. In order to reduce variability, only clinically healthy animals enter the study as their health status is assessed in entry examination. Like humans, pigs can also suffer from congenital heart disease, such as an atrial septal defect (ASD), which often remains undetected. Due to the malformation of the endocardial cushion during organ development, mitral valve defects (e.g., mitral clefts) are sometimes associated with ASDs, further contributing to hemodynamic instability. In this work, we report an incidental finding of a hemodynamically highly relevant ASD in the presence of incompetent mitral and tricuspid valves, in an asymptomatic, otherwise healthy juvenile pig. In-depth characterization of the cardiac blood flow by four-dimensional (4D) flow magnetic resonance imaging (MRI) revealed a prominent diastolic left-to-right and discrete systolic right-to-left shunt, resulting in a pulmonary-to-systemic flow ratio of 1.8. Severe mitral (15 mL/stroke) and tricuspid (22 mL/stroke) regurgitation further reduced cardiac output. Pathological examination confirmed the presence of an ostium primum ASD and found a serous cyst of lymphatic origin that was filled with clear fluid partially occluding the ASD. A large mitral cleft was identified as the most likely cause of severe regurgitation, and histology showed mild to moderate endocardiosis in the coaptation area of both atrio-ventricular valves. In summary, although not common, congenital heart defects could play a role as a cause of experimental variability or even intra-experimental mortality when working with apparently heathy, juvenile pigs.

Inhaled nitric oxide preserves ventricular function during resuscitation using a percutaneous mechanical circulatory support device in a porcine cardiac arrest model: an echocardiographic myocardial work analysis

Background

Resuscitation using a percutaneous mechanical circulatory support device (iCPR) improves survival after cardiac arrest (CA). We hypothesized that the addition of inhaled nitric oxide (iNO) during iCPR might prove synergistic, leading to improved myocardial performance due to lowering of right ventricular (RV) afterload, left ventricular (LV) preload, and myocardial energetics. This study aimed to characterize the changes in LV and RV function and global myocardial work indices (GWI) following iCPR, both with and without iNO, using 2-D transesophageal echocardiography (TEE) and GWI evaluation as a novel non-invasive measurement.

Methods

In 10 pigs, iCPR was initiated following electrically-induced CA and 10 min of untreated ventricular fibrillation (VF). Pigs were randomized to either 20 ppm (20 ppm, n = 5) or 0 ppm (0 ppm, n = 5) of iNO in addition to therapeutic hypothermia for 5 h following ROSC. All animals received TEE at five pre-specified time-points and invasive hemodynamic monitoring.

Results

LV end-diastolic volume (LVEDV) increased significantly in both groups following CA. iCPR alone led to significant LV unloading at 5 h post-ROSC with LVEDV values reaching baseline values in both groups (20 ppm: 68.2 ± 2.7 vs. 70.8 ± 6.1 mL, p = 0.486; 0 ppm: 70.8 ± 1.3 vs. 72.3 ± 4.2 mL, p = 0.813, respectively). LV global longitudinal strain (GLS) increased in both groups following CA. LV-GLS recovered significantly better in the 20 ppm group at 5 h post-ROSC (20 ppm: − 18 ± 3% vs. 0 ppm: − 13 ± 2%, p = 0.025). LV-GWI decreased in both groups after CA with no difference between the groups. Within 0 ppm group, LV-GWI decreased significantly at 5 h post-ROSC compared to baseline (1,125 ± 214 vs. 1,835 ± 305 mmHg%, p = 0.011). RV-GWI was higher in the 20 ppm group at 3 h and 5 h post-ROSC (20 ppm: 189 ± 43 vs. 0 ppm: 108 ± 22 mmHg%, p = 0.049 and 20 ppm: 261 ± 54 vs. 0 ppm: 152 ± 42 mmHg%, p = 0.041). The blood flow calculated by the Impella controller following iCPR initiation correlated well with the pulsed-wave Doppler (PWD) derived pulmonary flow (PWD vs. controller: 1.8 ± 0.2 vs. 1.9 ± 0.2L/min, r = 0.85, p = 0.012).

Conclusions

iCPR after CA provided sufficient unloading and preservation of the LV systolic function by improving LV-GWI recovery. The addition of iNO to iCPR enabled better preservation of the RV-function as determined by better RV-GWI. Additionally, Impella-derived flow provided an accurate measure of total flow during iCPR.