Left ventricular remodeling after infarction: sequential MR imaging with oral nicorandil therapy in rat model

Effects of Compound Danshen Dripping Pills on Ventricular Remodeling and Cardiac Function after Acute Anterior Wall ST-Segment Elevation Myocardial Infarction (CODE-AAMI): Protocol for a Randomized Placebo-Controlled Trial

BACKGROUND

Ventricular remodeling after acute anterior wall ST-segment elevation myocardial infarction (AAMI) is an important factor in occurrence of heart failure which additionally results in poor prognosis. Therefore, the treatment of ventricular remodeling needs to be further optimized. Compound Danshen Dripping Pills (CDDP), a traditional Chinese medicine, exerts a protective effect on microcirculatory disturbance caused by ischemia-reperfusion injury and attenuates ventricular remodeling after myocardial infarction.

OBJECTIVE

This study is designed to evaluate the efficacy and safety of CDDP in improving ventricular remodeling and cardiac function after AAMI on a larger scale.

METHODS

This study is a multi-center, randomized, double-blind, placebo-controlled, parallel-group clinical trial. The total of 268 patients with AAMI after primary percutaneous coronary intervention (pPCI) will be randomly assigned 1:1 to the CDDP group (n=134) and control group (n=134) with a follow-up of 48 weeks. Both groups will be treated with standard therapy of ST-segment elevation myocardial infarction (STEMI), with the CDDP group administrating 20 tablets of CDDP before pPCI and 10 tablets 3 times daily after pPCI, and the control group treated with a placebo simultaneously. The primary endpoint is 48-week echocardiographic outcomes including left ventricular ejection fraction (LVEF), left ventricular end-diastolic volume index (LVEDVI), and left ventricular end-systolic volume index (LVESVI). The secondary endpoint includes the change in N terminal pro-B-type natriuretic peptide (NT-proBNP) level, arrhythmias, and cardiovascular events (death, cardiac arrest, or cardiopulmonary resuscitation, rehospitalization due to heart failure or angina pectoris, deterioration of cardiac function, and stroke). Investigators and patients are both blinded to the allocated treatment.

DISCUSSION

This prospective study will investigate the efficacy and safety of CDDP in improving ventricular remodeling and cardiac function in patients undergoing pPCI for a first AAMI. Patients in the CDDP group will be compared with those in the control group. If certified to be effective, CDDP treatment in AAMI will probably be advised on a larger scale. (Trial registration No. NCT05000411).

Modification on acute myocardial infarction model through left anterior descending coronary artery ligation: An experimental study on rats (Rattus norvegicus) using readily available materials

BACKGROUND AND AIM

Several difficulties are involved in creating models for myocardial infarction (MI) in animals, such as low survival rates after acute MI, complicated techniques in creating animal models, complexities in confirming acute MI incidence, and complex surgical tools needed in the process. This study aimed to develop an animal model for acute MI using Wistar rats utilizing simple instruments that are readily available in standard animal laboratories.

MATERIALS AND METHODS

We induced MI in 48 Wistar rats using the left anterior descending coronary artery ligation modification technique without tracheal incision and ventilator. This ligation technique was performed 1-2 mm distal to the left atrial appendage. MI occurrence was evaluated using heart enzyme parameters 24 h post-ligation and histological studies of the infarcted area 6 weeks after the ligation. Rats were divided into the coronary artery ligation group and sham group.

RESULTS

Of the 48 rats, 24 (50%) died within 24 h post-ligation, but no further deaths occurred in the next follow-up period of 6 weeks. The average infarct size in six rats within 24 h of ligation was 35%±5.7%. The serum glutamic oxaloacetic transaminase level of the group treated with coronary artery ligation was statistically significantly higher than that of the sham group (p=0.000).

CONCLUSION

We developed an MI rat model with consistent infarction size, in which the long-term death of rats was not observed. Our ligation technique for an MI rat model can be a reference for experimental settings without ventilators for small animals.

Guidelines for experimental models of myocardial ischemia and infarction

Myocardial infarction is a prevalent major cardiovascular event that arises from myocardial ischemia with or without reperfusion, and basic and translational research is needed to better understand its underlying mechanisms and consequences for cardiac structure and function. Ischemia underlies a broad range of clinical scenarios ranging from angina to hibernation to permanent occlusion, and while reperfusion is mandatory for salvage from ischemic injury, reperfusion also inflicts injury on its own. In this consensus statement, we present recommendations for animal models of myocardial ischemia and infarction. With increasing awareness of the need for rigor and reproducibility in designing and performing scientific research to ensure validation of results, the goal of this review is to provide best practice information regarding myocardial ischemia-reperfusion and infarction models.

Listen to this article’s corresponding podcast at ajpheart.podbean.com/e/guidelines-for-experimental-models-of-myocardial-ischemia-and-infarction/.

Magnetic Resonance Imaging of Reverse Remodeling After Coronary Revascularization in Ischemic Heart Disease - Morphologic Evaluation

BACKGROUND

Coronary revascularization has been shown to induce left ventricular (LV) reverse remodeling (RR). The serial morphologic changes in enhanced necrotic tissue during RR on cardiac magnetic resonance imaging (CMR) have not been investigated.

METHODS AND RESULTS

This retrospective study included 26 patients with severe LV systolic dysfunction (ejection fraction [EF], <35% on echocardiography) who underwent CMR before and >6 months after surgical revascularization. Of 26 patients, 20 had a reduction of ≥10% in end-diastolic and end-systolic volumes (classified as RR group). The RR group had improvement in EF after revascularization (28.8±6.6% vs. 40.6±7.8%, P<0.0001), and no change in absolute infarct mass (17.3±10.9 g vs. 17.5±10.4 g, P=0.8), but an increase in relative infarct mass (21.0±13.7% vs. 26.5±19.4%, P=0.01) due to reduction of myocardial mass after revascularization. Significant increase in regional transmural extent (30.3±21.6 vs. 42.6±22.8, P<0.0001) and in thickness of enhanced tissue (4.2±1.5 mm vs. 5.9±1.8 mm, P<0.0001) was found in the RR group. No significant differences were observed in any of the variables in the non-RR group.

CONCLUSIONS

In patients with chronic myocardial ischemic dysfunction, significant volume reduction after revascularization led to significant increase in regional transmural extent of the enhanced area without a change in absolute infarct mass, on CMR. (Circ J 2016; 80: 2513-2519).

Myocardial protective effects of nicorandil, an opener of potassium channels on senile rat heart

The purpose of this study was to investigate the cardio-protective effects of nicorandil, an opener of potassium channels, on senile rat hearts from ischemic reperfusion injury.

A modified working model of isolated perfused hearts of senile rats was used. After isolation, the hearts underwent 60 min of global hypothermic ischemia treatment, followed by 30 min of reperfusion. These hearts were distributed into three groups, each receiving different cardioplegic solutions: (1) St. Thomas’ solution (Group S), (2) 100 μmol/L nicorandil (Group N), (3) St. Thomas’ solution combined with 100 μmol/L nicorandil (Group S+N). The pre- and post-ischemic myocardial function were assessed by the percentage recovery of the heart rate (HR), ±dp/dtmax (maximal rate of change of left ventricular pressure) and cardiac output (CO). Upon reperfusion, the cardioplegic solution was collected from the coronary sinus and tested for lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) activity.

During 30 min of reperfusion, the percentage recovery of HR, +dp/dt and left ventricular stroke work (LVSW) were significantly higher in Group S+N than in Group S and Group N ( p < 0.05). The percentage of recovery in CO was higher in Group N and Group S+N than in Group S. The electrical activities arresting time (EAT) and mechanical activities arresting time (MAT) were longer in Group N than in Group S and Group N+S( p < 0.01). There were no statistical significance between Group S and Group N+ S( p > 0.05). There were no significant differences in the levels of LDH and CK-MB. Electron microscopic examination revealed better preservation of the ultra-structures of the myocardial tissue in Group N+S than the other two groups.

These results indicate that nicorandil combined with St. Thomas’ solution can improve the left ventricular function of the post-ischemic senile rat and offer a better myocardial protective effect on the ischemic senile myocardium.

Why Is Infarct Expansion Such an Elusive Therapeutic Target?

Myocardial infarct expansion has been associated with an increased risk of infarct rupture and progression to heart failure, motivating therapies such as infarct restraint and polymer injection that aim to limit infarct expansion. However, an exhaustive review of quantitative studies of infarct remodeling reveals that only half found chronic in-plane expansion, and many reported in-plane compaction. Using a finite element model, we demonstrate that the balance between scar stiffening due to collagen accumulation and increased wall stresses due to infarct thinning can produce either expansion or compaction in the pressurized heart-potentially explaining variability in the literature-and that loaded dimensions are much more sensitive to changes in thickness than in stiffness. Our analysis challenges the concept that in-plane expansion is a central feature of post-infarction remodeling; rather, available data suggest that radial thinning is the dominant process during infarct healing and may be an attractive therapeutic target.

Analysis of left ventricular function of the mouse heart during experimentally induced hyperthyroidism and recovery

Many of the clinical manifestations of hyperthyroidism are due to the ability of thyroid hormones to alter myocardial contractility and cardiovascular hemodynamics, leading to cardiovascular impairment. In contrast, recent studies highlight also the potential beneficial effects of thyroid hormone administration for clinical or preclinical treatment of different diseases such as atherosclerosis, obesity and diabetes or as a new therapeutic approach in demyelinating disorders. In these contexts and in the view of developing thyroid hormone-based therapeutic strategies, it is, however, important to analyze undesirable secondary effects on the heart. Animal models of experimentally induced hyperthyroidism therefore represent important tools for investigating and monitoring changes of cardiac function. In our present study we use high-field cardiac MRI to monitor and follow-up longitudinally the effects of prolonged thyroid hormone (triiodothyronine) administration focusing on murine left ventricular function. Using a 9.4 T small horizontal bore animal scanner, cinematographic MRI was used to analyze changes in ejection fraction, wall thickening, systolic index and fractional shortening. Cardiac MRI investigations were performed after sustained cycles of triiodothyronine administration and treatment arrest in adolescent (8 week old) and adult (24 week old) female C57Bl/6 N mice. Triiodothyronine supplementation of 3 weeks led to an impairment of cardiac performance with a decline in ejection fraction, wall thickening, systolic index and fractional shortening in both age groups but with a higher extent in the group of adolescent mice. However, after a hormonal treatment cessation of 3 weeks, only young mice are able to partly restore cardiac performance in contrast to adult mice lacking this recovery potential and therefore indicating a presence of chronically developed heart pathology.

Nicorandil prevents right ventricular remodeling by inhibiting apoptosis and lowering pressure overload in rats with pulmonary arterial hypertension

Background

Most of the deaths among patients with severe pulmonary arterial hypertension (PAH) are caused by progressive right ventricular (RV) pathological remodeling, dysfunction, and failure. Nicorandil can inhibit the development of PAH by reducing pulmonary artery pressure and RV hypertrophy. However, whether nicorandil can inhibit apoptosis in RV cardiomyocytes and prevent RV remodeling has been unclear.

Methodology/Principal Findings

RV remodeling was induced in rats by intraperitoneal injection of monocrotaline (MCT). RV systolic pressure (RVSP) was measured at the end of each week after MCT injection. Blood samples were drawn for brain natriuretic peptide (BNP) ELISA analysis. The hearts were excised for histopathological, ultrastructural, immunohistochemical, and Western blotting analyses. The MCT-injected rats exhibited greater mortality and less weight gain and showed significantly increased RVSP and RV hypertrophy during the second week. These worsened during the third week. MCT injection for three weeks caused pathological RV remodeling, characterized by hypertrophy, fibrosis, dysfunction, and RV mitochondrial impairment, as indicated by increased levels of apoptosis. Nicorandil improved survival, weight gain, and RV function, ameliorated RV pressure overload, and prevented maladaptive RV remodeling in PAH rats. Nicorandil also reduced the number of apoptotic cardiomyocytes, with a concomitant increase in Bcl-2/Bax ratio. 5-hydroxydecanoate (5-HD) reversed these beneficial effects of nicorandil in MCT-injected rats.

Conclusions/Significance

Nicorandil inhibits PAH-induced RV remodeling in rats not only by reducing RV pressure overload but also by inhibiting apoptosis in cardiomyocytes through the activation of mitochondrial ATP-sensitive K⁺ (mitoK_ATP) channels. The use of a mitoK_ATP channel opener such as nicorandil for PAH-associated RV remodeling and dysfunction may represent a new therapeutic strategy for the amelioration of RV remodeling during the early stages of PAH.

Delayed contrast enhancement on MR images of myocardium: past, present, future

Differential enhancement of myocardial infarction was first recognized on computed tomographic (CT) images obtained with iodinated contrast material in the late 1970s. Gadolinium enhancement of myocardial infarction was initially reported for T1-weighted magnetic resonance (MR) imaging in 1984. The introduction of an inversion-recovery gradient-echo MR sequence for accentuation of the contrast between normal and necrotic myocardium was the impetus for widespread clinical use for demonstrating the extent of myocardial infarction. This sequence has been called delayed-enhancement MR and MR viability imaging. The physiologic basis for differential enhancement of myocardial necrosis is the greater distribution volume of injured myocardium compared with that of normal myocardium. It is now recognized that delayed enhancement occurs in both acute and chronic (scar) infarctions and in an array of other myocardial processes that cause myocardial necrosis, infiltration, or fibrosis. These include myocarditis, hypertrophic cardiomyopathy, amyloidosis, sarcoidosis, and other myocardial conditions. In several of these diseases, the presence and extent of delayed enhancement has prognostic implications. Future applications of delayed enhancement with development of MR imaging and CT techniques will be discussed.

Left ventricular apical diseases

There are many disorders that may involve the left ventricular (LV) apex; however, they are sometimes difficult to differentiate. In this setting cardiac imaging methods can provide the clue to obtaining the diagnosis. The purpose of this review is to illustrate the spectrum of diseases that most frequently affect the apex of the LV including Tako-Tsubo cardiomyopathy, LV aneurysms and pseudoaneurysms, apical diverticula, apical ventricular remodelling, apical hypertrophic cardiomyopathy, LV non-compaction, arrhythmogenic right ventricular dysplasia with LV involvement and LV false tendons, with an emphasis on the diagnostic criteria and imaging features.

Speckle tracking imaging improves in vivo assessment of EPO-induced myocardial salvage early after ischemia-reperfusion in rats

A noninvasive assessment of infarct size and transmural extension of myocardial infarction (TEMI) is fundamental in experimental models of ischemia-reperfusion. Conventional echocardiography parameters are limited in this purpose. This study was designed to examine whether speckle tracking imaging can be used in a rat model of ischemia-reperfusion to accurately detect the reduction of infarct size and TEMI induced by erythropoietin (EPO) as early as 24 h after reperfusion. Rats were randomly assigned to one of three groups: myocardial infarction (MI)-control group, 45 min ischemia followed by 24 h of reperfusion; MI-EPO group, similar surgery with a single bolus of EPO administered at the onset of reperfusion; and sham-operated group. Short-axis two-dimensional echocardiography was performed after reperfusion. Global radial (GSr) and circumferential (GScir) strains were compared with infarct size and TEMI assessed after triphenyltetrazolium chloride staining. As a result, ejection fraction, shortening fraction, GSr, and GScir significantly correlated to infarct size, whereas only GSr and GScir significantly correlated to TEMI. EPO significantly decreased infarct size (30.8 ± 3.5 vs. 56.2 ± 5.7% in MI-control, P < 0.001) and TEMI (0.37 ± 0.05 vs. 0.77 ± 0.05 in MI-control, P < 0.001). None of the conventional echocardiography parameters was significantly different between the MI-EPO and MI-control groups, whereas GSr was significantly higher in the MI-EPO group (29.1 ± 4.7 vs. 16.4 ± 3.3% in MI-control; P < 0.05). Furthermore, GScir and GSr appeared to be the best parameters to identify a TEMI >0.75 24 h after reperfusion. In conclusion, these findings demonstrate the usefulness of speckle tracking imaging in the early evaluation of a cardioprotective strategy in a rat model of ischemia-reperfusion.

Effect of ATP-sensitive potassium channel agonists on ventricular remodeling in healed rat infarcts

OBJECTIVES

The purpose of this study was to determine whether ATP-sensitive potassium (K(ATP)) channel agonists exert a beneficial effect on the structural, functional, and molecular features of the remodeling heart in infarcted rats.

BACKGROUND

Myocardial K(ATP) channels have been implicated in the ventricular remodeling after myocardial infarction by inhibition of 70-kDa S6 (p70S6) kinase.

METHODS

Male Wistar rats after induction of myocardial infarction were randomized to either vehicle, agonists of K(ATP) channels nicorandil and pinacidil, an antagonist of K(ATP) channels glibenclamide, or a combination of nicorandil and glibenclamide or pinacidil and glibenclamide for 4 weeks. To verify the role of p70S6 kinase in ventricular remodeling, rapamycin was also assessed.

RESULTS

Significant ventricular hypertrophy was detected by increased myocyte size at the border zone isolated by enzymatic dissociation after infarction. Increased synthesis of p70S6 kinase messenger ribonucleic acid after infarction in vehicle-treated rats was confirmed by reverse transcription-polymerase chain reaction, consistent with the results of immunohistochemistry and Western blot for phosphorylated p70S6 kinase. Rats in the nicorandil- and pinacidil-treated groups significantly attenuated cardiomyocyte hypertrophy and phosphorylated p70S6 kinase expression with similar potency, as compared with vehicle. The beneficial effects of nicorandil and pinacidil were abolished by administering either glibenclamide or 5-hydroxydecanoate. Addition of rapamycin attenuated ventricular remodeling and did not have additional beneficial effects compared with those seen in rats treated with either nicorandil or pinacidil alone.

CONCLUSIONS

Activation of K(ATP) channels by either nicorandil or pinacidil can attenuate ventricular remodeling, probably through a p70S6 kinase-dependent pathway after infarction.

Effects of sulfonylureas on left ventricular mass in type 2 diabetic patients

Myocardial ATP-sensitive potassium (KATP) channels have been implicated in attenuating cardiac hypertrophy by modulating endothelin-1 concentrations. Sulfonylureas differ in their affinity for cardiac KATPchannels and therefore may vary in their effects on left ventricular (LV) mass. We sought to determine the differential effects of sulfonylureas on LV mass in type 2 diabetic patients. All patients had been taking glibenclamide for more than 3 mo before being randomized to either switch to an equipotent dose of gliclazide or continue glibenclamide. A total of consecutive 240 diabetic patients were randomized into glibenclamide, gliclazide, a combination of glibenclamide and nicorandil, or gliclazide and nicorandil for 6 mo. In the gliclazide-treated group, the LV mass index was significantly decreased compared with that in the glibenclamide-treated groups. Nicorandil administration significantly reduced LV mass in glibenclamide-treated patients compared with patients treated with glibenclamide alone. Measurements of endothelin-1 concentrations mirrored the functional status of KATPchannel. Multivariate analysis revealed that regression of LV mass was significantly correlated only with the changes in endothelin-1 ( P < 0.0001). Our results show that KATPchannels may play a pathogenetic role, probably through an endothelin-1-dependent pathway, in diabetes mellitus-related ventricular hypertrophy. Patients treated with gliclazide may have a beneficial effect in attenuating ventricular mass.

Effects of pravastatin on ventricular remodeling by activation of myocardial KATP channels in infarcted rats: role of 70-kDa S6 kinase

Reactive cardiomyocyte hypertrophy after myocardial infarction is an important risk factor for arrhythmias. Myocardial ATP-sensitive potassium (K(ATP)) channels have been implicated in attenuating cardiac hypertrophy by inhibition of 70-kDa S6 kinase. We investigated the effect of pravastatin on ventricular hypertrophy during remodeling after myocardial infarction and whether the attenuated hypertrophic effect was via activation of myocardial K(ATP) channels. Twenty-four hours after ligation of the anterior descending artery, male Wistar rats were randomized to either vehicle, nicorandil (an agonist of K(ATP) channels), pravastatin, glibenclamide (an antagonist of K(ATP) channels), or a combination of nicorandil and glibenclamide or pravastatin and glibenclamide for 4 weeks. Infarct size and mortality were similar among the infarcted groups. Cardiomyocyte sizes isolated by enzymatic dissociation after infarction significantly increased at the border zone in vehicle-treated infarcted rats compared with sham-operated rats. Rats in the nicorandil- and pravastatin-treated groups significantly attenuated cardiomyocyte hypertrophy, as compared with the vehicle-treated group. Arrhythmic scores during programmed stimulation mirrored those of cardiomyocyte hypertrophy. Increased 70-kDa S6 kinase mRNA expression in cardiac remodeling was confirmed by reverse transcription-polymerase chain reaction, consistent with the results of immunohistochemistry and Western blot for the phosphorylation of 70-kDa S6 kinase. Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, the beneficial effects of pravastatin were abolished by administering glibenclamide, implicating K(ATP) channels as the relevant target. Activation of K(ATP) channels by pravastatin administration can attenuate ventricular remodeling through a S6 kinase-dependent pathway after infarction.

Optimization of cardiac cine in the rat on a clinical 1.5-T MR system

OBJECT

The overall goal was to study cardiovascular function in small animals using a clinical 1.5-T MR scanner optimizing a fast gradient-echo cine sequence to obtain high spatial and temporal resolution.

MATERIALS AND METHODS

Normal rat hearts (n = 9) were imaged using a 1.5-T MR scanner with a spiral fast gradient-echo (fast field echo for Philips scanners) sequence, three Cartesian fast gradient-echo (turbo field echo for Philips scanners) sequences with different in-plane resolution, and with and without flow compensation and half-Fourier acquisition. The hearts of four rats were then excised and left-ventricle mass was weighed. Inter- and intra-observer variability analysis was performed for magnetic resonance imaging (MRI) measurements.

RESULTS

Half-Fourier acquisition with flow compensation gave the best sequence in terms of image quality, spatial as well as temporal resolution, and suppression of flow artifact. Ejection fraction was 71 +/- 4% with less than 5% inter- and intra-observer variability. A good correlation was found between MRI-calculated left-ventricular mass and wet weight.

CONCLUSIONS

Using optimized sequences on a clinical 1.5-T MR scanner can provide accurate quantification of cardiac function in small animals and can promote cardiovascular research on small animals at 1.5-T.

Nicorandil but not ISDN Upregulates Endothelial Nitric Oxide Synthase Expression, Preventing Left Ventricular Remodeling and Degradation of Cardiac Function in Dahl Salt-sensitive Hypertensive Rats With Congestive Heart Failure

Cardiac endothelial nitric oxide synthase (ecNOS) was suppressed and inducible NOS (iNOS) enhanced at the decompensated heart failure stage in 18-week-old Dahl salt-sensitive (DS) hypertensive rats to which a high-salt diet had been administered from the age of 6 weeks. Nicorandil (NIC) enhanced ecNOS by activating Adenosine triphosphate-sensitive potassium channels (K-ATP channels) in the normal rat left ventricle. In this study, left ventricular hypertrophy, remodeling, function, cardiac ecNOS, and iNOS were compared between NIC and isosorbide dinitrate (ISDN) treatments in DS hypertensive rats with congestive heart failure. We examined DS hypertensive rats of 18 weeks of age to which 8% NaCl had been administered from the age of 6 weeks, and to which subdepressor doses of NIC (6 mg/kg/d), ISDN (6 mg/kg/d), and vehicle (CON) were administered from the age of 11 weeks. Contractility (Ees), stiffness (Eed), left ventricular end-diastolic volume, and left ventricular end-systolic volume were measured by conductance catheter and micromanometer on the basis of the pressure-volume relationship, and mRNA and protein levels of ecNOS and iNOS in the left ventricle were measured by reverse transcription-polymerase chain reaction and Western blot analysis at 18 weeks. LV mass index and LV dimensions were smaller in the NIC and ISDN groups than in the CON group (P < 0.01), and the first parameter was lower in the NIC than in the ISDN group (P < 0.01). Ees was also better maintained in the NIC and ISDN groups than in the CON group (NIC: 3349 +/- 649; ISDN: 2950 +/- 577, P < 0.05 vs. NIC; CON: 1424 +/- 375 mL/mmHg, P < 0.01 vs. treatments). Eed was exacerbated only in the ISDN group. NIC enhanced whereas ISDN suppressed ecNOS mRNA and protein levels (NIC 2.0-fold and 1.8-fold, ISDN 0.70-fold and 0.8-fold vs. CON; P < 0.01, respectively). However, no intragroup differences in iNOS mRNA or protein levels were observed for the 3 groups. More significant improvements in cardiac function and LV hypertrophy regression were observed in an NIC group than in an ISDN group of DS hypertensive rats. Activation of the K-ATP channel seems to induce this beneficial effect, which may be mediated in part by enhanced ecNOS expression in the heart in DS hypertensive congestive heart failure rat model.

Serial magnetic resonance imaging based assessment of the early effects of an ACE inhibitor on postinfarction left ventricular remodeling in rats

In vivo assessment of treatment efficacy on postinfarct left ventricular (LV) remodeling is crucial for experimental studies. We examined the technical feasibility of serial magnetic resonance imaging (MRI) for monitoring early postinfarct remodeling in rats. MRI studies were performed with a 7-Tesla unit, 1, 3, 8, 15, and 30 days after myocardial infarction (MI) or sham operation, to measure LV mass, volume, and the ejection fraction (EF). Three groups of animals were analyzed: sham-operated rats (n = 6), MI rats receiving lisinopril (n = 11), and MI rats receiving placebo (n = 8). LV dilation occurred on day 3 in both MI groups. LV end-systolic and end-diastolic volumes were significantly lower in lisinopril-treated rats than in placebo-treated rats at days 15 and 30. EF was lower in both MI groups than in the sham group at all time points, and did not differ between the MI groups during follow-up. Less LV hypertrophy was observed in rats receiving lisinopril than in rats receiving placebo at days 15 and 30. We found acceptable within- and between-observer agreement and an excellent correlation between MRI and ex vivo LV mass (r = 0.96; p < 0.001). We demonstrated the ability of MRI to detect the early beneficial impact of angiotensin-converting enzyme (ACE) inhibitors on LV remodeling. Accurate and noninvasive, MRI is the tool of choice to document response to treatment targeting postinfarction LV remodeling in rats.

Gadomer-enhanced MR Imaging in the Detection of Microvascular Obstruction: Alleviation with Nicorandil Therapy

PURPOSE

To evaluate Gadomer-enhanced magnetic resonance (MR) imaging in the quantification of small microvascular obstruction regions and determine if nicroandil alleviates the formation of microvascular obstruction.

MATERIALS AND METHODS

Approval of the institutional committee on animal research was obtained, and this study complied with guidelines for care and use of animals. Rats underwent coronary artery occlusion and reperfusion. After 24 hours, Gadomer-enhanced T1-weighted spin-echo MR imaging was used to define microvascular obstruction in animals in control and nicorandil groups. Sequential MR images obtained at two midventricular levels were acquired to measure microvascular obstruction and ischemically injured regions and monitor diffusive and/or convective transport of Gadomer in microvascular obstruction regions. Two investigators working in consensus and using threshold signal intensity measured differentially enhanced regions. Left-ventricular (LV) end-systolic and end-diastolic MR images obtained at the same two midventricular levels were used to measure regional wall thickening and systolic reduction in LV relative volumes. Agreement and correlation between MR imaging and postmortem data were determined with Bland-Altman and linear regression analyses. Animals were sacrificed 3 minutes after intravenous injection of blue dye.

RESULTS

On Gadomer-enhanced MR images, two differentially enhanced regions were observed in ischemically injured myocardium, namely, the hypoenhanced region and the surrounding hyperenhanced region. Hypoenhanced regions at MR imaging and unstained regions at blue dye administration were identical 3 minutes after administration (17% +/- 1 and 17% +/- 2; P = .6; r = 0.98). In the control group, Gadomer provided a prolonged imaging window (eg, 6 minutes) for accurately quantifying small microvascular obstruction regions. Microvascular obstruction was observed in all animals in the control group and 27% of animals in the nicorandil group. Microvascular obstruction regions were smaller in the nicorandil group (eg, 3% +/- 1) than in the control group (eg, 17% +/- 2) (P < .001). Hyper- and hypoenhanced regions were also smaller (eg, 20% +/- 2) in rats in the nicorandil group than in those in the control group (37% +/- 4, P < .001). Improvement in LV function in the nicorandil group is likely related to alleviation and reduction in infarct size.

CONCLUSION

Gadomer-enhanced MR imaging can be used to quantify small microvascular obstruction regions 24 hours after reperfusion. Intravenous therapy with nicorandil reduces formation of microvascular obstruction regions.

Long-Term Oral Treatment with Nicorandil Prevents the Progression of Left Ventricular Hypertrophy and Preserves Viability

Left ventricular (LV) hypertrophy and myocardial infarction play important roles in the progressive LV dysfunction. We hypothesized that the potassium-channel opener and nitrate-like vasodilator nicorandil prevents the development of LV hypertrophy and preserves myocardial viability. Twenty-four rats were subjected to aortic stenosis for 8 weeks to produce LV hypertrophy and assigned to non-treated and nicorandil-treated (3 mg/kg/d) groups. A third group (n = 12) without stenosis or treatment served as control. All 36 animals were subjected to reperfused infarction by 25-minute occlusion of the left coronary artery followed by 3 hours of reperfusion. Spin-echo magnetic resonance (MR) images were acquired to measure infarction size, LV mass, volumes, ejection fraction, and wall thickness. A necrosis-specific contrast agent, Gadophrin-3, was used to delineate necrotic myocardium. Aortic and LV pressures were measured invasively. At postmortem, LV mass and infarction size were determined and compared with MR findings. Nicorandil prevented the development of LV hypertrophy. Infarction size of nicorandil-treated animals was similar to control animals. Non-treated animals with aortic banding had higher LV mass (P < 0.001), lower ejection fraction (P = 0.006), and larger infarction size (P < 0.001) than treated and control animals. MR and postmortem data showed close agreement. Nicorandil therapy prevented the development of cardiac hypertrophy and protected myocardium against ischemia.

Effect of pravastatin on left ventricular mass by activation of myocardial K ATP channels in hypercholesterolemic rabbits

Epidemiological studies showed that hypercholesterolemia was associated with a higher left ventricular mass. Myocardial ATP-sensitive potassium (K(ATP)) channels have been implicated in the development of cardiac hypertrophy. We investigated the effect of pravastatin on hypercholesterolemia-induced ventricular hypertrophy and whether the attenuated hypertrophic effect was via activation of myocardial K(ATP) channels. In this study, we evaluated the hemodynamic, biochemical, and morphological responses to pravastatin in cholesterol-fed (1%) rabbits. Male New Zealand White rabbits were randomized to either vehicle, nicorandil (an agonist of K(ATP) channels), pravastatin, glibenclamide (an antagonist of K(ATP) channels), or a combination of nicorandil and glibenclamide or pravastatin and glibenclamide for 8 weeks. The left ventricular weight and left ventricular myocyte sizes increased 8 weeks after cholesterol-feeding in comparison to that in normocholesterolemic rabbits. Pravastatin administration significantly decreased the left ventricular weight by 12% and cardiomyocyte cell areas by 30%. Hyperlipidemic rabbits in the nicorandil- and pravastatin-treated groups significantly attenuated cardiomyocyte hypertrophy, as compared with the vehicle-treated group (3162 +/- 277 microm(2), 3372 +/- 228 microm(2) versus 4388 +/- 163 microm(2) in the vehicle group, both P < 0.0001, respectively). Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, pravastatin-induced beneficial effects were reversed by the addition of glibenclamide, implicating K(ATP) channels as the relevant target. The results of the present study suggest a pathogenetic role of K(ATP) channels in hypercholesterolemia-induced ventricular hypertrophy. The antihypertropic effects of pravastatin may be related to activation of K(ATP) channels, and result in an amelioration of cardiomyocyte hypertrophy development by an atherogenic diet.

Current status of cardiac MRI in small animals

Cardiac magnetic resonance imaging (MRI) on small animals is possible but remains challenging and not well standardized. This publication aims to provide an overview of the current techniques, applications and challenges of cardiac MRI in small animals for researchers interested in moving into this field. Solutions have been developed to obtain a reliable cardiac trigger in both the rat and the mouse. Techniques to measure ventricular function and mass have been well validated and are used by several research groups. More advanced techniques like perfusion imaging, delayed enhancement or tag imaging are emerging. Regarding cardiac applications, not only coronary ischemic disease but several other pathologies or conditions including cardiopathies in transgenic animals have already benefited from these new developments. Therefore, cardiac MRI has a bright future for research in small animals.

The potential of contrast-enhanced magnetic resonance imaging for predicting left ventricular remodeling

PURPOSE

To determine whether the myocardial injury size on day 2 measured after gadolinium (Gd)-mesoporphyrin and Gd-diethylenetriamine-pentaacetic acid (DTPA) administration can be used for predicting left ventricular (LV) remodeling 8 weeks later, and to monitor the structural and functional changes in the infarct, peri-infarct rim, and remote myocardium in reperfused infarction using contrast-enhanced and functional magnetic resonance imaging (MRI) MATERIALS AND METHODS: Myocardial infarction (MI) was induced in 27 rats by 1 hour of coronary occlusion/reperfusion. Rats were imaged 2 days and 8 weeks after MI using MRI to determine LV function and size of myocardial injury. All animals received 0.05 mmol/kg Gd-mesoporphyrin 12 hours before the first MRI. A subgroup of 13 rats received 0.3 mmol/kg Gd-DTPA in addition to Gd-mesoporphyrin, and seven rats received 0.05 mmol/kg Gd-mesoporphyrin 12 hours before the second MRI for detection of healed MI. True infarct size (IS) and LV mass were measured postmortem. LV volumes, mass, function, and wall thickness were determined in both imaging sessions.

RESULTS

A close correlation was found between contrast-enhanced MRI and postmortem measurements for IS (r = 0.94, P < 0.001 for Gd-mesoporphyrin; r = 0.91, P < 0.001, N = 13 for Gd-DTPA). IS measured on Gd-mesoporphyrin-enhanced images correlated well with end-systolic LV volumes (r = 0.68, P < 0.001) and ejection fraction (r = -0.75, P < 0.001) 8 weeks after MI. Similar correlation with parameters of LV remodeling were found on Gd-DTPA-enhanced MRI. Healed infarcts showed no enhancement on Gd-mesoporphyrin-enhanced MRI.

CONCLUSION

Contrast-enhanced MRI can be used as a noninvasive method for determining the initial size of myocardial injury and predicting later LV remodeling. MRI demonstrates the structural and functional changes in infarct, peri-infarct rim, and remote non-infarcted myocardium. The complementary use of functional and contrast-enhanced MRI may provide reliable assessment of therapeutic interventions to reduce IS and LV remodeling.