Evaluation of cardiac structures and function in small experimental animals: transthoracic, transesophageal, and intraventricular echocardiography to assess contractile function in rat heart

A pooled analysis of nine studies in one institution to assess effects of whole heart irradiation in rat models

PURPOSE

Over the years, animal models of local heart irradiation have provided insight into mechanisms of and treatments for radiation-induced heart disease in human populations. However, it is not completely clear which manifestations of radiation injury are most commonly seen after whole heart irradiation, and whether certain biological factors impact experimental results. Combining 9 homogeneous studies in rat models of whole heart irradiation from one laboratory, we sought to identify experimental and/or biological factors that impact heart outcomes. We evaluated the usefulness of including (1) heart rate and (2) bodyweight as covariates when analyzing biological parameters, and (3) we determined which echocardiography, histological, and immunohistochemistry parameters are most susceptible to radiation effects. Finally, (4) as an educational example, we illustrate a hypothetical sample size calculation for a study design commonly used in evaluating radiation modifiers, using the pooled estimates from the 9 rat studies only for context. The results may assist investigators in the design and analyses of pre-clinical studies of whole heart irradiation.

MATERIALS AND METHODS

We made use of data from 9 rat studies from our labs, 8 published elsewhere in 2008-2017, and one unpublished study. Echocardiography, histological, and immunohistochemical parameters were collected from these studies. Using mixed effects analysis of covariance models, we estimated slopes for heart rate and bodyweight and estimated the radiation effect on each of the parameters.

RESULTS

Bodyweight was related to most echocardiography parameters, and heart rate had an effect on echocardiography parameters related to the diameter of the left ventricle. For some parameters, there was evidence that heart rate and bodyweight relationships with the parameter depended on whether the rats were irradiated. Radiation effects were found in systolic measures of echocardiography parameters related to the diameter of the left ventricle, with ejection fraction and fractional shortening, with atrial wall thickness, and with histological measures of capillary density, collagen deposition, and mast cells infiltration in the heart.

CONCLUSION

Accounting for bodyweight, as well as heart rate, in analyses of echocardiography parameters should reduce variability in estimated radiation effects. Several echocardiography and histological parameters were particularly susceptible to whole heart irradiation, showing robust effects compared to sham-irradiation. Lastly, we provide an example approach for a sample size calculation that will contribute to a rigorous study design and reproducibility in experiments studying radiation modifiers.

Comparison of Intramyocardial and Intravenous Routes of Delivering Bone Marrow Cells for the Treatment of Ischemic Heart Disease: An Experimental Study

The implantation of bone marrow cells (BMCs) into ischemic heart after myocardial infarction can induce angiogenesis and improve heart function. We compared the advantages of delivering BMCs intramyocardially and intravenously. An acute myocardial infarction model was created by the ligation of left anterior descending artery in female Dark Agouti rats. The rats were then randomly divided into four treatment groups: one given an intramyocardial injection of phosphate-buffered saline (PBS group), one given an intravenous injection of 2 × 107 BMCs from male rats (IV group), one given an intramyocardial injection with total of 2 × 107 BMCs from male rats at four points in the infarction area (IM group), and one given an intravenous injection of 10-fold the number of BMCs from male rats (10xIV group). Quantitative analysis of the SRY gene by real-time PCR showed that the survival of BMCs in the infarcted area was significantly higher in the IM group than in the IV and 10xIV groups, 3 days after treatment (p < 0.05), but not thereafter. However, the blood flow in the infarcted myocardium was significantly better in the IM and 10xIV groups than in the PBS and IV groups 14 days after treatment (p < 0.05). Echocardiography showed that the LVEF continued to decrease in the PBS and IV groups, but was stable after 3 days in the IM and 10xIV groups. By 14 days after treatment, the LVEF was significantly higher in the IM and 10xIV groups than in the PBS and IV groups (p < 0.01). Our results showed that BMCs were more effective delivered intramyocardially than intravenously for inducing angiogenesis and repairing injured myocardium.

Fetal origins of adult cardiac disease: a novel approach to prevent fetal growth restriction induced cardiac dysfunction using insulin like growth factor

BACKGROUND

Fetal growth restriction (FGR) is a risk factor for adult cardiovascular disease. Intraplacental gene transfer of human insulin-like growth factor-1 (IGF-1) corrects birth weight in our mouse model of FGR. This study addresses long term effects of FGR on cardiac function and the potential preventive effect of IGF-1.

STUDY DESIGN

Laparotomy was performed on pregnant C57BL/6J mice at embryonic day 18 and pups were divided into three groups: Sham operated; FGR (induced by mesenteric uterine artery ligation); treatment (intraplacental injection of IGF-1 after uterine artery ligation). Pups were followed until 32 wk of life. Transthoracic echocardiography was performed starting at 12 wk.

RESULTS

Systolic cardiac function was significantly impaired in the FGR group with reduced fractional shortening compared with sham and treatment group starting at week 12 of life (20 ± 4 vs. 31 ± 5 vs. 32 ± 5, respectively, n = 12 for each group; P < 0.001) with no difference between the sham and treatment groups.

CONCLUSION

Intraplacental gene transfer of IGF-1 prevents FGR induced cardiac dysfunction. This suggests that in utero therapy may positively impact cardiac remodeling and prevent adult cardiovascular disease.

Multiple impairments of cutaneous nociceptor function induced by cardiotoxic doses of Adriamycin in the rat

Besides their deleterious action on cardiac muscle, anthracycline-type cytostatic agents exert significant neurotoxic effects on primary sensory neurons. Since cardiac sensory nerves confer protective effects on heart muscle and share common traits with cutaneous chemosensitive nerves, this study examined the effects of cardiotoxic doses of adriamycin on the function and morphology of epidermal nerves. Sensory neurogenic vasodilatation, plasma extravasation, and the neural CGRP release evoked by TRPV1 and TRPA1 agonists in vitro were examined by using laser Doppler flowmetry, the Evans blue technique, and ELISA, respectively. Carrageenan-induced hyperalgesia was assessed with the Hargreaves method. Immunohistochemistry was utilized to study cutaneous innervation. Adriamycin treatment resulted in profound reductions in the cutaneous neurogenic sensory vasodilatation and plasma extravasation evoked by the TRPV1 and TRPA1 agonists capsaicin and mustard oil, respectively. The in vitro capsaicin-, but not high potassium-evoked neural release of the major sensory neuropeptide, CGRP, was markedly attenuated after adriamycin treatment. Carrageenan-induced inflammatory hyperalgesia was largely abolished following the administration of adriamycin. Immunohistochemistry revealed a substantial loss of epidermal TRPV1-expressing nociceptive nerves and a marked thinning of the epidermis. These findings indicate impairments in the functions of TRPV1 and TRPA1 receptors expressed on cutaneous chemosensitive nociceptive nerves and the loss of epidermal axons following the administration of cardiotoxic doses of adriamycin. Monitoring of the cutaneous nociceptor function in the course of adriamycin therapy may well be of predictive value for early detection of the deterioration of cardiac nerves which confer protection against the deleterious effects of the drug.

Increased susceptibility of spontaneously hypertensive rats to ventricular tachyarrhythmias in early hypertension

Hypertension is a risk factor for sudden cardiac death caused by ventricular tachycardia and fibrillation (VT/VF). We hypothesized that, in early hypertension, the susceptibility to stress-induced VT/VF increases. We compared the susceptibility of 5- to 6-month-old male spontaneously hypertensive rats (SHR) and age/sex-matched normotensive rats (NR) to VT/VF during challenge with oxidative stress (H2 O2 ; 0.15 mmol l(-1) ). We found that only SHR hearts exhibited left ventricular fibrosis and hypertrophy. H2 O2 promoted VT in all 30 SHR but none of the NR hearts. In 33% of SHR cases, focal VT degenerated to VF within 3 s. Simultaneous voltage-calcium optical mapping of Langendorff-perfused SHR hearts revealed that H2 O2 -induced VT/VF arose spontaneously from focal activations at the base and mid left ventricular epicardium. Microelectrode recording of SHR hearts showed that VT was initiated by early afterdepolarization (EAD)-mediated triggered activity. However, despite the increased susceptibility of SHR hearts to VT/VF, patch clamped isolated SHR ventricular myocytes developed EADs and triggered activity to the same extent as NR ventricular myocytes, except with larger EAD amplitude. During the early stages of hypertension, when challenged with oxidative stress, SHR hearts showed an increased ventricular arrhythmogenicity that stems primarily from tissue remodelling (hypertrophy, fibrosis) rather than cellular electrophysiological changes. Our findings highlight the need for early hypertension treatment to minimize myocardial fibrosis, ventricular hypertrophy, and arrhythmias.

Chronic Activation of Heme Free Guanylate Cyclase Leads to Renal Protection in Dahl Salt-Sensitive Rats

The nitric oxide (NO)/soluble guanylate cyclase (sGC)/cyclic guanosine monophasphate (cGMP)-signalling pathway is impaired under oxidative stress conditions due to oxidation and subsequent loss of the prosthetic sGC heme group as observed in particular in chronic renal failure. Thus, the pool of heme free sGC is increased under pathological conditions. sGC activators such as cinaciguat selectively activate the heme free form of sGC and target the disease associated enzyme. In this study, a therapeutic effect of long-term activation of heme free sGC by the sGC activator cinaciguat was investigated in an experimental model of salt-sensitive hypertension, a condition that is associated with increased oxidative stress, heme loss from sGC and development of chronic renal failure. For that purpose Dahl/ss rats, which develop severe hypertension upon high salt intake, were fed a high salt diet (8% NaCl) containing either placebo or cinaciguat for 21 weeks. Cinaciguat markedly improved survival and ameliorated the salt-induced increase in blood pressure upon treatment with cinaciguat compared to placebo. Renal function was significantly improved in the cinaciguat group compared to the placebo group as indicated by a significantly improved glomerular filtration rate and reduced urinary protein excretion. This was due to anti-fibrotic and anti-inflammatory effects of the cinaciguat treatment. Taken together, this is the first study showing that long-term activation of heme free sGC leads to renal protection in an experimental model of hypertension and chronic kidney disease. These results underline the promising potential of cinaciguat to treat renal diseases by targeting the disease associated heme free form of sGC.

Chemotherapy-induced changes in cardiac capillary permeability measured by fluorescent multiple indicator dilution

Anthracyclines cause severe irreversible cardiac toxicity. The study of changes in cardiac permeability with chemotherapy could enhance the understanding of mechanisms behind cardiac damage, and provide useful information to evaluate anthracycline cardiotoxicity. Thirty-six rats (12 Sprague-Dawley, 12 Wistar, 12 Fischer-344) were randomly assigned to control (n = 21) or doxorubicin (n = 15), and injected i.p. with a cumulative dose of 18 mg/kg doxorubicin in saline (vehicle) or vehicle alone over 12 days. Echocardiography was performed at baseline and on day 11. An isolated heart experiment was done on day 12 to obtain perfused heart pressure values, and to measure cardiac capillary permeability using a Texas Red/sodium fluorescein multiple indicator dilution method. Control animals had significantly lower average permeability-surface-area-products (0.035 ± 0.013 cm(3)/s) than doxorubicin animals (0.066 ± 0.023 cm(3)/s), PSP ± SD, p < 0.001. These permeability changes correlated with significant functional changes. There was a significant decline in cardiac function with a deleterious effect of chemotherapy on fractional shortening (p < 0.001), left ventricular developed pressure (p < 0.001), contractility (p < 0.001), and relaxation (p = 0.02). Based on our results, cardiac capillary permeability changes can be detected after in vivo chemotherapy treatment using our fluorescent multiple indicator dilution technique, and may provide valuable information in evaluating cardiotoxicity of novel drugs.

Cardiac magnetic resonance, transthoracic and transoesophageal echocardiography: a comparison of in vivo assessment of ventricular function in rats

In vivo assessment of ventricular function in rodents has largely been restricted to transthoracic echocardiography (TTE). However 1.5 T cardiac magnetic resonance (CMR) and transoesophageal echocardiography (TOE) have emerged as possible alternatives. Yet, to date, no study has systematically assessed these three imaging modalities in determining ejection fraction (EF) in rats. Twenty rats underwent imaging four weeks after surgically-induced myocardial infarction. CMR was performed on a 1.5 T scanner, TTE was conducted using a 9.2 MHz transducer and TOE was performed with a 10 MHz intracardiac echo catheter. Correlation between the three techniques for EF determination and analysis reproducibility was assessed. Moderate-strong correlation was observed between the three modalities; the greatest between CMR and TOE (intraclass correlation coefficient (ICC) = 0.89), followed by TOE and TTE (ICC = 0.70) and CMR and TTE (ICC = 0.63). Intra- and inter-observer variations were excellent with CMR (ICC = 0.99 and 0.98 respectively), very good with TTE (0.90 and 0.89) and TOE (0.87 and 0.84). Each modality is a viable option for evaluating ventricular function in rats, however the high image quality and excellent reproducibility of CMR offers distinct advantages even at 1.5 T with conventional coils and software.

Soluble guanylate cyclase stimulation prevents fibrotic tissue remodeling and improves survival in salt-sensitive Dahl rats

BACKGROUND

A direct pharmacological stimulation of soluble guanylate cyclase (sGC) is an emerging therapeutic approach to the management of various cardiovascular disorders associated with endothelial dysfunction. Novel sGC stimulators, including riociguat (BAY 63-2521), have a dual mode of action: They sensitize sGC to endogenously produced nitric oxide (NO) and also directly stimulate sGC independently of NO. Little is known about their effects on tissue remodeling and degeneration and survival in experimental malignant hypertension.

METHODS AND RESULTS

Mortality, hemodynamics and biomarkers of tissue remodeling and degeneration were assessed in Dahl salt-sensitive rats maintained on a high salt diet and treated with riociguat (3 or 10 mg/kg/d) for 14 weeks. Riociguat markedly attenuated systemic hypertension, improved systolic heart function and increased survival from 33% to 85%. Histological examination of the heart and kidneys revealed that riociguat significantly ameliorated fibrotic tissue remodeling and degeneration. Correspondingly, mRNA expression of the pro-fibrotic biomarkers osteopontin (OPN), tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) and plasminogen activator inhibitor-1 (PAI-1) in the myocardium and the renal cortex was attenuated by riociguat. In addition, riociguat reduced plasma and urinary levels of OPN, TIMP-1, and PAI-1.

CONCLUSIONS

Stimulation of sGC by riociguat markedly improves survival and attenuates systemic hypertension and systolic dysfunction, as well as fibrotic tissue remodeling in the myocardium and the renal cortex in a rodent model of pressure and volume overload. These findings suggest a therapeutic potential of sGC stimulators in diseases associated with impaired cardiovascular and renal functions.

Wideband high-frequency echocardiography to evaluate myocardial infarct size

OBJECTIVE

This study was designed to validate the feasibility of wideband high-frequency ultrasound imaging to resolve in vivo the degree, location, and morphologic changes of myocardial infarction (MI) in a rat model.

METHODS

The left anterior descending coronary artery was ligated in the test group (n = 41), and the sham control group did not have ligation (n = 7). The rats were examined with 10- to 22-MHz echocardiography to evaluate the MI size, location, and geometric formation.

RESULTS

The endocardial chamber shape was deformed, with enlargement of the anteroposterior dimension and fractional shortening, and was comparable with the degree of MI both in short- and long-axis sections of the left ventricle. Histologic analysis showed remodeling to different extents corresponding to different MI sizes (small, medium, and large).

CONCLUSIONS

The results suggest that this technique can be used in vivo to evaluate the MI location, size, and morphologic changes corresponding to the extent of the injury.

Intravascular ultrasound allows a hyperplasia diagnosis in vivo in rat as accurate as histomorphometry

OBJECTIVE AND MOTIVATION

Intravascular ultrasound (IVUS) allows in vivo invasive intra-luminal real-time examination of the arterial wall structure. In this study, we aimed to validate for the first time the in vivo IVUS performing as a diagnostic tool by comparison to the well-established histomorphometry approach, in the largely used rat model of carotid angioplasty model that mimics the angioplasty procedure in humans.

METHODS

Atherosclerotic lesions were allowed to develop during four weeks after balloon catheter inflation of the left carotid artery, whereas the intact right carotid artery was used as control. Four weeks after injury, a Boston Scientific 40MHz device to perform IVUS exams in vivo on both carotid arteries. Then, both carotid arteries were examined in vitro by histomorphometry and correlation between IVUS and histomorphometric parameters (plaque plus media cross-sectional areas [CSA] and eccentricity index) were researched.

RESULTS

After ANOVA analysis, comparative statistical analysis showed significant correlations between IVUS and histomorphometry when examining the intact right carotid artery (r=0.662 with p<0.003 for plaque plus media CSA; r=0.774 with p<0.002 for eccentricity index), but also when exploring the injured left carotid artery (r=0.805 with p<0.0001 for plaque plus media CSA; r=0.775 with p<0.002 for eccentricity index).

CONCLUSIONS AND OUTCOME

We report here for the first time the ability of IVUS to study therapeutic vascular effects in vivo in alive rats. This result is of major importance since it will allow this device to be used for restenosis drug testing in rat model of carotid angioplasty.

A thrombospondin-1 antagonist of transforming growth factor-beta activation blocks cardiomyopathy in rats with diabetes and elevated angiotensin II

In diabetes and hypertension, the induction of increased transforming growth factor-beta (TGF-beta) activity due to glucose and angiotensin II is a significant factor in the development of fibrosis and organ failure. We showed previously that glucose and angiotensin II induce the latent TGF-beta activator thrombospondin-1 (TSP1). Because activation of latent TGF-beta is a major means of regulating TGF-beta, we addressed the role of TSP1-mediated TGF-beta activation in the development of diabetic cardiomyopathy exacerbated by abdominal aortic coarctation in a rat model of type 1 diabetes using a peptide antagonist of TSP1-dependent TGF-beta activation. This surgical manipulation elevates initial blood pressure and angiotensin II. The hearts of these rats had increased TSP1, collagen, and TGF-beta activity, and cardiac function was diminished. A peptide antagonist of TSP1-dependent TGF-beta activation prevented progression of cardiac fibrosis and improved cardiac function by reducing TGF-beta activity. These data suggest that TSP1 is a significant mediator of fibrotic complications of diabetes associated with stimulation of the renin-angiotensin system, and further studies to assess the blockade of TSP1-dependent TGF-beta activation as a potential antifibrotic therapeutic strategy are warranted.

Reproducibility of transthoracic echocardiography in small animals using clinical equipment

OBJECTIVE

Transthoracic echocardiography has been employed to assess left ventricular dimensions and function in small animals. The aim of this study was to identify the limits of transthoracic echocardiography in a commonly used Wistar rat model by assessing intraobserver variability, interobserver variability, and day-to-day variability of examinations implying registrations and measurements.

METHODS

Twenty male adult Wistar rats (body weight 496+/-52 g) were examined under volatile isoflurane anesthesia (heart rate 302+/-26 bpm) by transthoracic echocardiography (Sonos 7500; Philips) with a 15 MHz-transducer. For calculation of intraobserver variability, examinations were repeated by the same examiner and for interobserver variability, examinations were performed independently by two investigators. For day-to-day variability, examinations were repeated 14 days later. Left ventricular diameters and areas were analyzed in parasternal short axis and in a modified parasternal long axis. Fractional shortening, area shortening, ejection fraction, stroke volume, and cardiac output were calculated.

RESULTS

Left ventricular end-diastolic diameter was 8.9+/-0.6 mm, fractional shortening 39.0+/-5.3%, area shortening 59.6+/-6.1%, ejection fraction 83.3+/-5.1%, stroke volume 0.24+/-0.06 ml, and cardiac output 72.9+/-20.6 ml/min. Intraobserver variability of left ventricular end-diastolic diameter, fractional shortening, area shortening, and ejection fraction was less than 10%, increasing to 19% for stroke volume and cardiac output. Interobserver variability of left ventricular end-diastolic diameter, fractional shortening, area shortening, ejection fraction was less than 13%, increasing to 23% for stroke volume and 25% for cardiac output. Day-to-day variability of left ventricular end-diastolic diameter, area shortening, ejection fraction was less than 11% whereas for stroke volume it was 21% and for cardiac output it was 22%. F-ratio test comparing investigated variabilities did not reveal significant differences.

CONCLUSIONS

M-mode and two-dimensional echocardiography in large rats by clinically common high-end ultrasound systems can be assessed reliably. Parameters of global left ventricular performance like stroke volume and cardiac output could not be assessed with similar reliability.

Computer-assisted navigation applied to fetal cardiac intervention

BACKGROUND

Prenatal cardiac interventions (PCI) for human fetal aortic valve (AoV) stenosis can reduce left ventricular hypoplasia and restore ventricular growth and function. However, 'freehand' needle delivery from the maternal skin through the uterine wall, fetal chest and ventricular apex to cross the fetal AoV remains technically challenging and time intensive, and is the rate-limiting step in the procedure.

METHODS

We developed a computer-assisted navigation (CANav) system that tracks the position and orientation of a two-dimensional (2D) ultrasound image relative to the trajectory of an electromagnetic (EM) embedded needle and stylet. We tested the CANav system in vitro using a water bath phantom, then in vivo using adult rats and pregnant (fetal) sheep.

RESULTS

The CANav system accurately tracked the delivered needle position in both in vitro phantom and adult rat model experiments. We performed 22 PCI attempts with or without CANav in a fetal sheep model. Maternal laparotomy was required to adjust the fetal position in 50% of the procedures. The time required to deliver the needle from the skin into the left ventricle (LV) using CANav was 2.9 +/- 1.7 (range 2-7) min (n = 14) vs. 5.5 +/- 4.3 (range 1-12) min (n = 8) without CANav (p < 0.05). The time needed to cross the aortic valve once the needle was within the LV was similar with and without CANav (p = 0.19).

CONCLUSIONS

CANav reduces the PCI time required to accurately deliver a needle to the fetal heart. Adaptations of this technical approach may be relevant to other congenital cardiac conditions and ultrasound-guided medical procedures.

An initial application of transesophageal Doppler echocardiography in experimental small animal models

This study examined whether an intracardiac echocardiography catheter could be used for transesophageal echocardiography (TEE) examinations in normal rats, and intraoperative TEE in small animal models of disease. The study used 30 Sprague-Dawley normal rats, 10 rats undergoing coronary artery ligation, and 10 rats with experimentally induced mitral regurgitation. The rats were anesthetized with isoflurane and intubated. An intracardiac echocardiographic catheter was inserted into the esophagus. M-mode, 2-dimensional, and Doppler studies were performed in multiple views. TEE probe insertions were successful in all animals. Intraoperative TEE was safely performed in the rat models of myocardial infarction or mitral regurgitation. Mitral regurgitation was well assessed using color Doppler and pulmonary venous flow. This study demonstrates that TEE (including intraoperative TEE) can be safely performed in rats using an intracardiac echocardiographic catheter. It provides a new approach to the assessment of cardiac function and valvular regurgitation in small animals.

Age-related changes in cardiac structure and function in Fischer 344 x Brown Norway hybrid rats

The effects of aging on cardiovascular function and cardiac structure were determined in a rat model recommended for gerontological studies. A cross-sectional analysis assessed cardiac changes in male Fischer 344 x Brown Norway F1 hybrid rats (FBN) from adulthood to the very aged (n = 6 per 12-, 18-, 21-, 24-, 27-, 30-, 33-, 36-, and 39-mo-old group). Rats underwent echocardiographic and hemodynamic analyses to determine standard values for left ventricular (LV) mass, LV wall thickness, LV chamber diameter, heart rate, LV fractional shortening, mitral inflow velocity, LV relaxation time, and aortic/LV pressures. Histological analyses were used to assess LV fibrotic infiltration and cardiomyocyte volume density over time. Aged rats had an increased LV mass-to-body weight ratio and deteriorated systolic function. LV systolic pressure declined with age. Histological analysis demonstrated a gradual increase in fibrosis and a decrease in cardiomyocyte volume density with age. We conclude that, although significant physiological and morphological changes occurred in heart function and structure between 12 and 39 mo of age, these changes did not likely contribute to mortality. We report reference values for cardiac function and structure in adult FBN male rats through very old age at 3-mo intervals.

Improvement of cardiac function by bone marrow cell implantation in a rat hypoperfusion heart model

BACKGROUND

Local bone marrow cell implantation can induce angiogenesis. In the present study we investigated whether angiogenesis induced by bone marrow cell implantation improves deteriorated cardiac function in a rat heart model of hypoperfusion.

METHODS

A hypoperfusion heart model was created in Dark Agouti rats by ligating the left anterior descending artery placed against a copper wire (phi275 microm), then pulling out the wire immediately. The left ventricular (LV) anterior wall was injected directly at six points, each with 1 x 10(7) bone marrow cells in 10 microL of phosphate-buffered saline or with phosphate-buffered saline only, respectively. Echocardiography was performed to evaluate the cardiac function 7, 30, 60, and 90 days after treatment. Microvessel density and blood flow in the LV anterior wall were estimated 60 days after treatment.

RESULTS

Both the increase of LV end-systolic diameter and the decrease of percent of fractional shortening caused by myocardial ischemia were attenuated effectively by bone marrow cell implantation treatment. Bone marrow cell implantation treatment also increased the levels of angiopoietin-1 and vascular endothelial growth factor in the LV anterior wall. The microvessel density, blood flow, and thickness of the LV anterior wall significantly also increased after bone marrow cell implantation treatment compared with those after phosphate-buffered saline injection.

CONCLUSIONS

The local implantation of autologous bone marrow cells induced angiogenesis and improved the perfusion of ischemic myocardium, thereby preventing LV remodeling and improving deteriorated cardiac function caused by myocardial hypoperfusion.

Echocardiographic measurement of cardiac output in rats

The systematic evaluation of different transthoracic echocardiographic (TTE) methods to determine cardiac output (CO) and the effect of changes in intravascular volume on echocardiographically determined indexes of cardiovascular structure in the rat has not been documented. With the use of 11 Wistar rats, simultaneous echocardiographic and thermodilution measurements of CO were compared at baseline and after blood withdrawal or transfusion at 43 different levels of intravascular volume and using 10 different echocardiographic approaches. The best correlation (r = 0.93; P < 0.0001), least bias (-3 ml/min), and best precision (16 ml/min) between thermodilution and echocardiographic methods were obtained at the level of aortic annulus using pulsed Doppler. In conclusion, CO could be accurately assessed in rats using TTE and pulsed Doppler at the level of the aortic annulus. This annulus was demonstrated to remain stable, but pulmonary annulus, thoracic aorta, mitral valve, and left ventricular diameters were found to be more modifiable during volumic changes.

Scar and pulmonary expression and shedding of ACE in rat myocardial infarction

We examined the topology of angiotensin-converting enzyme (ACE) mRNA expression, activity, and shedding in myocardial infarction-induced heart failure and sought to elucidate the source of the increased plasma ACE activity in this model. Three months after coronary ligature, lung, scar, and remaining viable left ventricular tissues were analyzed for ACE mRNA expression as well as tissue and solubilized ACE activity. ACE mRNA expression increased in the scar with respect to infarct severity, decreased in the lung, and remained unchanged in the left ventricle. ACE activity decreased in the lung and increased in the scar tissue and plasma. Shedding of ACE remained constant in the lung and increased in the scar. This study shows that ACE expression and activity is shifted from the pulmonary endothelium to the infarct scar tissue and that constancy of shedding in the lung and its increase in the scar are the source of the increased plasma ACE in congestive heart failure.

Doppler echocardiographic estimation of left ventricular end-diastolic pressure after MI in rats

The spectral Doppler mitral flow pattern, alone or combined with tissue Doppler mitral annulus velocity, can be used to predict left ventricular (LV) filling pressure in humans, whereas invasive hemodynamic measurements are still required in the rat. This study was undertaken to assess whether LV end-diastolic pressure (LVEDP) can be estimated using Doppler echocardiography in the rat after myocardial infarction (MI). Thirty-seven rats (23 rats with MI after left coronary artery ligation and 14 sham-operated rats) were evaluated 3 mo after surgery with echo-Doppler and invasive hemodynamic measurements. Pulse wave spectral Doppler at the mitral valve tip was used to measure the E wave, the E wave deceleration time (DT), and the A wave; spectral Doppler tissue imaging was used to measure the early diastolic lateral mitral annulus velocity (E(a)). We found weak correlations between LVEDP and the peak velocity of the early mitral inflow (E), E/peak velocity of the late mitral inflow, and DT, and strong correlations with E(a) and especially with E/E(a) [R(2) = 0.89, LVEDP (in mmHg) = 0.987E/E(a) - 4.229]. Longitudinal followup of a subgroup of rats with MI revealed a marked rise of E/E(a) between days 7 and 21 in rats with heart failure only. We conclude that Doppler echocardiography can be used for serial assessment of LV diastolic function in rats with MI.

Ultrasound imaging: principles and applications in rodent research

Ultrasound imaging utilizes the interaction of sound waves with living tissue to produce an image of the tissue or, in Doppler-based modes, determine the velocity of a moving tissue, primarily blood. These dynamic, real time images can be analyzed to obtain quantitative structural and functional information from the target organ. This versatile, noninvasive diagnostic tool is widely used and accepted in human and veterinary medicine. Until recently its application as a research tool was limited primarily to larger, nonrodent species. Due to advances in ultrasound imaging technology, commercially available ultrasound systems now have the spatial and temporal resolution to obtain accurate images of rat and mouse hearts, kidneys, and other target tissues including tumor masses. As a result, ultrasound imaging is being used more frequently as a research tool to image rats and mice, and particularly to evaluate cardiac structure and function. The developing technology of ultrasound biomicroscopy has even greater spatial resolution and has been used to evaluate developing mouse embryos and guide site-specific injections into mouse embryos. Additional ultrasound imaging technologies, including contrast-enhanced imaging and intravascular ultrasound transducers adapted for transesophageal use, have been utilized in rats and mice. This paper provides an overview of basic ultrasound principles, equipment, and research applications. The use of noninvasive ultrasound imaging in research represents both a significant refinement as a potential replacement for more invasive techniques and a significant advancement in research techniques to study rats and mice.

The fate of a tissue-engineered cardiac graft in the right ventricular outflow tract of the rat

OBJECTIVE

The synthetic materials currently available for the repair of cardiac defects are nonviable, do not grow as the child develops, and do not contract synchronously with the heart. We developed a beating patch by seeding fetal cardiomyocytes in a biodegradable scaffold in vitro. The seeded patches survived in the right ventricular outflow tract of adult rats.

METHODS

Cultured fetal or adult rat heart cells (1 x 10(6) cells) were seeded into a gelatin sponge (15 x 15 x 1 mm), and the cell number was expanded in culture for 1 or 3 weeks, respectively. The free wall of the right ventricular outflow tract in syngeneic adult rats was resected and repaired with either unseeded patches or patches seeded with either fetal or adult cardiomyocytes (n = 10 for each group). The patches were examined histologically over a 12-week period.

RESULTS

A significant inflammatory reaction was noted in the patch at 4 weeks as the scaffold dissolved. At 12 weeks, the gelatin scaffold had completely dissolved. Both types of the seeded cells were detected in the patch with 5-bromo-2'-deoxyuridine staining, and they maintained their continuity. Unseeded patches had an ingrowth of fibrous tissue. The patches became thinner between the fourth and the twelfth weeks in unseeded (P =.003), fetal (P =.0001), and adult (P =.07) cardiomyocyte groups as the scaffold dissolved. The control patch, but not the cell-seeded patches, was thinner than the normal right ventricular outflow tract. The endocardial surface area of each patch was covered with endothelial cells identified by factor VIII staining.

CONCLUSIONS

A gelatin patch was used to replace the right ventricular outflow tract in syngeneic rats. The seeded cells survived in the right ventricular outflow tract after the scaffold dissolved 12 weeks after implantation. In addition, the unseeded patches encouraged the ingrowth of fibrous tissue as the scaffold dissolved and the patches remained completely endothelialized.

Echocardiographic criteria for detection of postinfarction congestive heart failure in rats

We evaluated postinfarction myocardial function in rats and determined echocardiographic criteria for congestive heart failure (CHF) using high performance echocardiography. Extensive myocardial infarction (MI) was induced in rats by left coronary occlusion. Sham-operated animals served as controls. Five weeks later, high-frame rate ( approximately 200 Hz), fully digitized, shallow-focus (10-25 mm), two-dimensional, M-mode and Doppler echocardiography was performed. A J-tree cluster analysis was performed using parameters indicative of CHF. Reproducibility was examined. The cluster analysis joined the animals into one Sham and two MI clusters. One of the MI clusters had clinical characteristics of CHF and elevated left ventricular end diastolic pressure. Among the echocardiographic variables, only posterior wall shortening velocity separated the failing and nonfailing MI clusters. We conclude that, by high frame rate echocardiography, it is possible to obtain high- quality recordings in rats. It is feasible to distinguish MI rats with CHF due to myocardial dysfunction from those without failure and to perform longitudinal studies on myocardial function.

A new model of ventricular plication: a suturing technique to decrease left ventricular dimensions, improve contractility, and attenuate ventricular remodeling after myocardial infarction in the rat heart

BACKGROUND

The Batista procedure (cardio-reduction) is a surgical technique in patients with dilated cardiomyopathy that results in improvement of ventricular function. The purpose of this study was to test a new suturing technique without resection for cardio-reduction of myocardial infarct scars in rats.

METHODS AND RESULTS

Myocardial infarction (MI) was induced by occluding the left coronary artery 4 weeks before enrollment. Animals then were randomized to a control (n = 11) or treatment group (n = 11). A pursestring suture was placed within the border zones of the infarcted area and was either tightened (treated) or not (controls). Echocardiography was used to measure left ventricular diameters before, 1 hour, and 6 to 7 weeks after plication. Acutely after plication, end-diastolic length (EDL) decreased from 0.70 +/- 0.03 cm to 0.53 +/- 0.02 cm, P < .001; end-systolic length (ESL) decreased from 0.51 +/- 0.03 cm to 0.23 +/- 0.02 cm, P < .001; and fractional shortening (FS) increased from 27.6 +/- 1.5% to 57.6 +/- 2.3%, P < .001, whereas controls were unchanged. In control rats EDL increased from baseline at 0.73 +/- 0.02 cm to 0.82 +/- 0.04 cm at 6 weeks postsurgery, P < .05; ESL increased from 0.54 +/- 0.02 cm to 0.66 +/- 0.04 cm, P < .005; and FS decreased from 26.9 +/- 1.1% to 19.2 +/- 1.2% at 6 weeks, P < .05. In contrast, at 6 weeks in plicated animals, EDL was significantly less than controls at 0.64 +/- 0.02 cm, P < .005; ESL was significantly less than controls at 0.39 +/- 0.03 cm, P < .005, and FS was significantly better than controls at 40.5 +/- 2.2%, P < .005.

CONCLUSION

The progressive LV enlargement between 4 and 10 weeks after MI reflects late ventricular remodeling. Plication by suturing infarcted tissue acutely decreases diameters and improves function. At 6 weeks, function remains improved over untreated animals.