Transesophageal Echocardiography in Swine: Establishment of a Baseline

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).

Cardiac dimensions and hemodynamics in healthy juvenile Landrace swine

BACKGROUND

Swine are frequently used as animal model for cardiovascular research, especially in terms of representativity of human anatomy and physiology. Reference values for the most common species used in research are important for planning and execution of animal testing. Transesophageal echocardiography is the gold standard for intraoperative imaging, but can be technically challenging in swine. Its predecessor, epicardial echocardiography (EE), is a simple and fast intraoperative imaging technique, which allows comprehensive and goal-directed assessment. However, there are few echocardiographic studies describing echocardiographic parameters in juvenile swine, none of them using EE. Therefore, in this study, we provide a comprehensive dataset on multiple geometric and functional echocardiographic parameters, as well as basic hemodynamic parameters in swine using EE.

METHODS

The data collection was performed during animal testing in ten female swine (German Landrace, 104.4 ± 13.0 kg) before left ventricular assist device implantation. Hemodynamic data was recorded continuously, before and during EE. The herein described echocardiographic measurements were acquired according to a standardized protocol, encompassing apical, left ventricular short axis and long axis as well as epiaortic windows. In total, 50 echocardiographic parameters and 10 hemodynamic parameters were assessed.

RESULTS

Epicardial echocardiography was successfully performed in all animals, with a median screening time of 14 min (interquartile range 11-18 min). Referring to left ventricular function, ejection fraction was 51.6 ± 5.9% and 51.2 ± 6.2% using the Teichholz and Simpson methods, respectively. Calculated ventricular mass was 301.1 ± 64.0 g, as the left ventricular end-systolic and end-diastolic diameters were 35.3 ± 2.5 mm and 48.2 ± 3.5 mm, respectively. The mean heart rate was 103 ± 28 bpm, mean arterial pressure was 101 ± 20 mmHg and mean flow at the common carotid artery was 627 ± 203 mL/min.

CONCLUSION

Epicardial echocardiography allows comprehensive assessment of most common echocardiographic parameters. Compared to humans, there are important differences in swine with respect to ventricular mass, size and wall thickness, especially in the right heart. Most hemodynamic parameters were comparable between swine and humans. This data supports study planning, animal and device selection, reinforcing the three R principles in animal research.

Diazoxide preserves myocardial function in a swine model of hypothermic cardioplegic arrest and prolonged global ischemia

OBJECTIVE

Adenosine triphosphate potassium sensitive channels provide endogenous myocardial protection via coupling of cell membrane potential to myocardial metabolism. Adenosine triphosphate potassium sensitive channel openers, such as diazoxide, mimic ischemic preconditioning, prevent cardiomyocyte swelling, preserve myocyte contractility after stress, and provide diastolic protection. We hypothesize that diazoxide combined with hyperkalemic cardioplegia provides superior myocardial protection compared with cardioplegia alone during prolonged global ischemia in a large animal model.

METHODS

Twelve pigs were randomized to global ischemia for 2 hours with a single dose of cold blood (4:1) hyperkalemic cardioplegia alone (n = 6) or with diazoxide (500 μmol/L) (n = 6) and reperfused for 1 hour. Cardiac output, myocardial oxygen consumption, left ventricular developed pressure, left ventricular ejection fraction, diastolic function, myocardial troponin, myoglobin, markers of apoptosis, and left ventricular infarct size were compared.

RESULTS

Four pigs in the cardioplegia alone group could not be weaned from cardiopulmonary bypass. There were no differences in myoglobin, troponin, or apoptosis between groups. Diazoxide preserved cardiac output versus control (74.5 vs 18.4 mL/kg/min, P = .01). Linear mixed regression modeling demonstrated that the addition of diazoxide to cardioplegia preserved left ventricular developed pressure by 36% (95% confidence interval, 9.9-61.5; P < .01), dP/dt max by 41% (95% confidence interval, 14.5-67.5; P < .01), and dP/dt min by 33% (95% confidence interval, 8.9-57.5; P = .01). It was also associated with higher (but not significant) myocardial oxygen consumption (3.7 vs 1.4 mL O2/min, P = .12).

CONCLUSIONS

Diazoxide preserves systolic and diastolic ventricular function in a large animal model of prolonged global myocardial ischemia. Diazoxide as an adjunct to hyperkalemic cardioplegia may allow safer prolonged ischemic times during increasingly complicated cardiac procedures.

Left Ventricular Function in the Initial Period After Severe Traumatic Brain Injury in Swine

BACKGROUND

Cardiac dysfunction is common in the days after severe traumatic brain injury (TBI) and may contribute to hypotension episodes, leading to worse outcomes. Little is known about cardiac function in the minutes and hours immediately following TBI. By using fluid percussion TBI in a swine model, we aimed to characterize the immediate post injury cardiac function.

METHODS

Intubated, anesthetized immature (25.8 ± 1.5 kg) female swine were subjected to severe fluid percussion TBI (4.2 ± 0.2 atm). Beginning at 45 min, simulating hospital arrival, all animals were resuscitated with normal saline (NS), mannitol, and phenylephrine as needed to maintain a cerebral perfusion pressure more than 60 mm Hg and intracranial pressure (ICP) less than 20 mm Hg. Primary outcomes of cardiac function were cardiac output measured by thermodilution and transesophageal echo measurements of cardiac function recorded at prespecified time points and tested for trends over time using linear regression with spline at the time of resuscitation onset. Secondary outcomes included hemodynamic measurements, ICP, and cerebral perfusion pressure.

RESULTS

Eighteen animals were included. Post-TBI hemodynamic changes demonstrated an early decrease in mean arterial pressure and cerebral perfusion pressure with a corresponding increase in heart rate and ICP. Immediately after injury, there was a significant decrease in both left atrial area and tissue Doppler imaging e' of the LV lateral wall. In addition, there was a simultaneous increase in LV end diastolic diameter and increase in E/e' ratio of the lateral mitral annulus. All other transesophageal echo measurements demonstrated no significant changes throughout the duration of the experiment.

CONCLUSIONS

Traumatic brain injury is associated with cardiac dysfunction and increased mortality, however there is still a limited understanding of the hemodynamic and echocardiographic response associated with TBI. In this study we demonstrate the hemodynamic and echocardiographic changes in the early stages of TBI in swine. The authors hope that these results may help better understanding on the management of patients with severe head injury.

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

This study aimed to determine standard left (LV) and right ventricular (RV) transesophageal echocardiographic (TEE) measurements in swine. Additionally, global myocardial work index (GWI) was estimated using pressure-strain loops (PSL). A comprehensive TEE examination was conducted in ten anesthetized, intubated and mechanically ventilated healthy female German landrace swine, weighing 44 to 57 kg. For GWI calculation, we performed LV and RV segmental strain analysis and used invasively measured LV and RV pressure to obtain PSL. The GWI and further myocardial work indices were calculated from the area of the PSL using commercially available software. Furthermore, hemodynamic measurements were obtained using indwelling catheters. We obtained complete standardized baseline values for left and right ventricular dimensions and function. Biplane LV ejection fraction was 63 ± 7 % and the LV end-diastolic volume was 70.5 ± 5.9 ml. Tissue Doppler estimated peak tricuspid annular systolic velocity was 13.1 ± 1.8 cm/s. The Doppler estimated LV and RV stroke volume index were 75.6 ± 7.2 ml/m2 and 76.7 ± 7.8 ml/m2 respectively. Pulsed wave Doppler derived cardiac output correlated well with cardiac output estimated using the thermodilution method (7.0 ± 1.2 l/min vs. 7.0 ± 1.1 l/min, r = 0.812, p = 0.004). The LV global longitudinal strain was -21.3 ± 3.9 % and the RV global longitudinal strain was -15.4 ± 2.5 %. LV GWI was 1885(1281-2121) mmHg*% and 297 ± 62 mmHg*% for the RV. LV global myocardial work efficiency was 82.6 ± 4 % and 83(72-88) % for the RV. TEE offers sufficient morphological, functional and hemodynamic assessment of the heart in swine. Myocardial contractility and mechanics can be reliably evaluated with the non-invasive GWI derived from echocardiography without additional invasive measures.

Carbon monoxide improves haemodynamics during extracorporeal resuscitation in pigs

AIMS

Heart disease of different aetiology remains the leading cause of cardiac arrest (CA). Despite efforts to improve the quality of cardiopulmonary resuscitation (CPR), subsequent myocardial and systemic damage after CA still present a major long-term burden. Low-dose carbon monoxide (CO) is known to exert protective effects in cardiovascular pathophysiology but clinical applications are challenged by unfavourable delivery modes. We tested the hypothesis that extracorporeal resuscitation (E-CPR) in combination with controlled fast onset CO delivery results in improved cardiac physiology and haemodynamics. Damage-associated molecular pattern (DAMP) signalling may be part of the molecular mechanism.

METHODS AND RESULTS

In an established porcine model, E-CPR was performed. While E-CPR leads to similar results as compared to a conventional CPR strategy, CO delivery in combination with E-CPR demonstrated significant cardioprotection. Cardiac performance analysis using echocardiography and thermodilution techniques showed a CO-dependent improved cardiac function compared to severe myocardial dysfunction in CPR and E-CPR (left ventricular ejection fraction: Sham 49 ± 5; CPR 26 ± 2; E-CPR 25 ± 2; CO-E-CPR 31 ± 4; P < 0.05). While sublingual microcirculation was significantly compromised in CPR and E-CPR, CO delivery demonstrated a significant improvement in microvascular function (microvascular flow index: Sham 2.9 ± 0.1; CPR 2.2 ± 0.1; E-CPR 1.8 ± 0.1; CO-E-CPR 2.7 ± 0.1; P < 0.01). Histological and serological myocardial damage markers were significantly reduced (hsTroponin-T Sham 0.01 ± 0.001; CPR 1.9 ± 0.2; E-CPR 3.5 ± 1.2; CO-E-CPR 0.5 ± 0.2 ng/mL; P < 0.05). DAMP signalling was decreased ipse facto leading to influence of cardioprotective heat shock and cyclooxygenase response.

CONCLUSIONS

CO treatment restores myocardial function and improves systemic macro- and microhaemodynamics in E-CPR through a reduction in DAMPs.

Transapical septal myectomy in the beating heart via a minimally invasive approach: a feasibility study in swine

OBJECTIVES

The aim of this study was to establish an original transapical septal myectomy procedure that can be performed in the beating heart via a minimally invasive approach for the treatment of hypertrophic obstructive cardiomyopathy.

METHODS

We designed an original intracardiac septum resection device to conduct off-pump septal myectomy in swine. A subxiphoid minithoracotomy was performed to access the apex of the heart. This resection device was inserted into the left ventricular outflow tract of the heart via the apex. The basal anteroseptal myocardium beneath the right aortic cusp was identified using a combination of transoesophageal and transthoracic echocardiography and then resected and collected by the device.

RESULTS

Six consecutive operations were successfully and accurately performed using the custom-made device under echocardiographic guidance. All pigs survived and appeared to be normal until planned euthanasia 1 week after operation. A 300-700 mg portion of the septal myocardium was resected from the normal swine heart. Echocardiography and electrocardiogram revealed no abnormalities after resection. One exception was the fifth pig, in which mild annular regurgitation of the aortic valve occurred after repetitive resection. Postmortem necropsy demonstrated that all resections were correctly located at the basal anteroseptal septum beneath the right aortic cusp.

CONCLUSIONS

Our study provides the first proof-of-concept evidence for a novel beating heart transapical septal myectomy procedure, which showed promising translational potential for the treatment of hypertrophic obstructive cardiomyopathy. This procedure would probably reduce operative risks and improve outcomes and reduce the demanding expertise required to perform conventional surgical myectomy.

A Pilot Study of Third-Generation Dual-Source Computed Tomography for the Assessment of Global Dynamic Changes in Left Ventricular Structure and Function in a Porcine Model of Acute Myocardial Infarction

Background

First-generation and second-generation dual-source computed tomography (DSCT) are useful for analyzing left ventricle (LV) structure and function. This pilot study aimed to investigate the feasibility and role of third-generation DSCT for the evaluation of dynamic changes in LV structural and functional characteristics in a Diannan small-ear pig model of acute myocardial infarction (AMI).

Material/Methods

The model of AMI was established by balloon occlusion of the distal third of the left anterior descending (LAD) coronary artery in 14 Diannan small-eared pigs. Third-generation DSCT was performed to observe dynamic changes in LV structure and function before and after AMI was induced, with a follow-up period of 30 days.

Results

The mean structural measurements at baseline included interventricular septum thickness (8.50±0.90 mm), LV anterior wall thickness (8.40±1.30 mm), LV posterior wall thickness (7.80±1.20 mm), LV end-diastolic dimension (LVEDD) (45.00±4.90 mm), and LV end-systolic dimension (LVESD) (25.90±4.10 mm). The mean functional measurements at baseline included the LV end-diastolic volume (LVEDV) (74.62±13.54 ml), LV end-systolic volume (LVESV) (23.06±7.46 ml), LV ejection fraction (LVEF) (69.29±6.83%), LV mass (86.35±14.02 g), stroke volume (SV) (51.56±9.77 ml), and cardiac output (CO) (4.22±2.14 l/min). Trends of time-dependent changes were observed for LVESV, LVEF, SV, and CO, but not for LVEDV or LV mass.

Conclusions

Third-generation DSCT was validated as a tool for assessing dynamic changes in LV global function in a porcine model of AMI.

Feasibility of basic transesophageal echocardiography in hemorrhagic shock: potential applications during resuscitative endovascular balloon occlusion of the aorta (REBOA)

Background

There are numerous studies in the cardiovascular literature that have employed transesophageal echocardiography (TEE) in swine models, but data regarding the use of basic TEE in swine models is limited. The primary aim of this study is to describe an echocardiographic method that can be used with relative ease to qualitatively assess cardiovascular function in a porcine hemorrhagic shock model using resuscitative endovascular balloon occlusion of the aorta (REBOA).

Methods

Multiplane basic TEE exams were performed in 15 during an experimental hemorrhage model using REBOA. Cardiac anatomical structure and functional measurements were obtained. In a convenience sample (two animals from each group), advanced functional cardiovascular measurements were obtained before and after REBOA inflation for comparison with qualitative assessments.

Results

Basic TEE exams were performed in 15 swine. Appropriate REBOA placement was confirmed using TEE in all animals and verified with fluoroscopy. Left ventricular volume was decreased in all animals, and left ventricular systolic function increased following REBOA inflation. Right ventricular systolic function and volume remained normal prior to and after hemorrhage and REBOA use. Mean ejection fraction (EF) decreased from 64% (S.D. 9.6) to 62.1 (S.D. 16.8) after hemorrhage and REBOA inflation (p = 0.76); fractional area of change (FAC) decreased from 49.8 (S.D. 9.0) to 48.5 (S.D. 13.6) after hemorrhage and REBOA inflation (p = 0.82).

Conclusion

Basic TEE, which requires less training than advanced TEE, may be employed by laboratory investigators and practitioners across a wide spectrum of experimental and clinical settings.