Myocardial infarction scar plication in the rat: cardiac mechanics in an animal model for surgical procedures

Noninvasive and Invasive Study of the Pumping Function of Rat Heart in Myocardial Infarction

The cardiohemodynamics was studied 2 and 4 weeks after myocardial infarction modeling in Wistar rats. We compared the data obtained by echocardiography (echoCG) and catheterization of the left ventricle. The myocardial infarction was modeled by ligation of the left anterior descending coronary artery. EchoCG and the left ventricle catheterization were performed before and after myocardial infarction modeling. Similar results were obtained by both methods, namely the left ventricle dilatation, bradycardia, a reduced ejection fraction and delayed relaxation. According to echoCG, the end-diastolic left ventricle volume increased by 2 times, and initial diastolic left ventricle volume - by more than 5 times. The left ventricle catheterization showed lower rise, by 32 and 69%, respectively. The overestimated volume of the left ventricle in myocardial infarction according to echoCG data in comparison with catheterization can be explained by changes in the geometry of the ventricle (bulging of a part of the ventricular wall).

METTL3 improves cardiomyocyte proliferation upon myocardial infarction via upregulating miR-17-3p in a DGCR8-dependent manner

Myocardial infarction (MI), one of the most severe types of heart attack, exerts a strong negative effect on heart muscle by causing a massive and rapid loss of cardiomyocytes. However, the existing therapies do little to improve cardiac regeneration. Due to the role of methyltransferase-like 3 (METTL3) in the physiological proliferation of cardiomyocytes, we aimed to determine whether METTL3 could also promote cardiomyocyte proliferation under pathological conditions and to elucidate the underlying mechanism. The effects of METTL3 on cardiomyocyte proliferation and apoptosis were investigated in an in vivo rat model of MI and in an in vitro model of neonatal rat cardiomyocytes (NRCMs) exposed to hypoxia. We found that METTL3 expression was downregulated in hypoxia-exposed NRCMs and MI-induced rats. Furthermore, METTL3 pretreatment enhanced cardiomyocyte proliferation and inhibited cardiomyocyte apoptosis under hypoxic or MI conditions, and silencing METTL3 had the opposite effects. Additionally, METTL3 overexpression upregulated miR-17-3p expression. The miR-17-3p agomir mimicked the pro-proliferative and antiapoptotic effects of METTL3 in hypoxia-exposed cells or rats with MI, while the miR-17-3p antagomir blocked these effects. Additionally, pretreatment with the RNA-binding protein DGCR8 also hampered the protective role of METTL3 in hypoxia-exposed cells. Overall, the current study indicated that METTL3 could improve cardiomyocyte proliferation and subsequently ameliorate MI in rats by upregulating proliferation-related miR-17-3p in a DGCR8-dependent pri-miRNA-processing manner.

Hyperbaric oxygenation improves redox control and reduces mortality in the acute phase of myocardial infarction in a rat model

Among the mechanisms of action of hyperbaric oxygenation (HBO), the chance of reducing injury by interfering with the mechanisms of redox homeostasis in the heart leads to the possibility of extending the period of viability of the myocardium at risk. This would benefit late interventions for reperfusion to the ischemic area. The objective of the present study was to investigate the changes in the redox system associated with HBO therapy maintained during the first hour after coronary occlusion in an acute myocardial infarction (MI) rat model. Surviving male rats (n=105) were randomly assigned to one of three groups: Sham (SH=26), myocardial infarction (MI=45) and infarction+hyperbaric therapy (HBO=34, 1 h at 2.5 atm). After 90 min of coronary occlusion, a sample of the heart was collected for western blot analysis of total protein levels of superoxide dismutase, catalase, peroxiredoxin and 3‑nitrotyrosine. Glutathione was measured by enzyme‑linked immunosorbent assay (ELISA). The detection of the superoxide radical anion was carried out by oxidation of dihydroethidium analyzed with confocal microscopy. The mortality rate of the MI group was significantly higher than that of the HBO group. No difference was noted in the myocardial infarction size. The oxidized/reduced glutathione ratio and peroxiredoxin were significantly higher in the SH and MI when compared to the HBO group. Superoxide dismutase enzymes and catalase were significantly higher in the HBO group compared to the MI and SH groups. 3‑Nitrotyrosine and the superoxide radical were significantly lower in the HBO group compared to these in the MI and SH groups. These data demonstrated that hyperbaric oxygenation therapy decreased mortality by improving redox control in the hearts of rats in the acute phase of myocardial infarction.

Digitoxin Attenuates Heart Failure, Reduces Myocardial Hypertrophy, and Preserves the Calcium-Binding Proteins in Infarcted Rats

We previously showed that digitoxin prolongs the survival of rats with heart failure due to myocardial infarction (MI). In this study, we evaluated the effect of digitoxin on myocardial structure, ventricular function, and proteins involved in calcium kinetics. Seventy-two rats with MI >35% of the left ventricle were randomly assigned to 4 treatment groups: sham (n = 15), digitoxin (n = 11), infarction (n = 20), and infarction + digitoxin (n = 26). The rats were assessed 120 days after surgery by echocardiogram, hemodynamics, papillary muscle mechanics, collagen content, cardiomyocyte nuclear volume, and Western blot analysis of proteins involved in calcium kinetics. Digitoxin was administered via the rat chow. Two-way analysis of variance was used for comparisons. Myocardial infarction caused inotropic impairment, pulmonary congestion, increase of nuclear volume, myocardial collagen, and Na⁺/Ca2⁺ exchanger levels, and decreased SERCA2 and phosphorylated phospholamban levels. Treatment with digitoxin showed improvements in cardiac remodeling, inotropism, ventricular performance, pulmonary congestion, collagen accumulation, nuclear volume, and proteins involved in calcium kinetics. In rats with heart failure due to MI, long-term treatment with digitoxin attenuates congestive heart failure, mitigates myocardial remodeling and contractile impairment, and preserves myocardial levels of proteins involved in calcium kinetics.

Are there gender differences in left ventricular remodeling after myocardial infarction in rats?

Objective

An unclear issue is whether gender may influence at cardiac remodeling after myocardial infarction (MI). We evaluated left ventricle remodeling in female and male rats post-MI.

Methods

Rats were submitted to anterior descending coronary occlusion. Echocardiographic evaluations were performed on the first and sixth week post-occlusion to determine myocardial infarction size and left ventricle systolic function (FAC, fractional area change). Pulsed Doppler was applied to analyze left ventricle diastolic function using the following parameters: E wave, A wave, E/A ratio. Two-way ANOVA was applied for comparisons, complemented by the Bonferroni test. A P≤=0.05 was considered significant.

Results

There were no significant differences between genders for morphometric parameters on first (MI [Female (FE): 44.0±5.0 vs. Male (MA): 42.0±3.0%]; diastolic [FE: 0.04±0.003 vs. MA: 0.037±0.005, mm/g] and systolic [FE: 0.03±0.0004 vs. MA: 0.028±0.005, mm/g] diameters of left ventricle) and sixth (MI [FE: 44.0±5.0 vs. MA: 42.0±3.0, %]; diastolic [FE: 0.043±0.01 vs. MA: 0.034±0.005, mm/g] and systolic [FE: 0.035±0.01 vs. MA: 0.027±0.005, mm/g] of LV) week. Similar findings were reported for left ventricle functional parameters on first (FAC [FE: 34.0±6.0 vs. MA: 32.0±4.0, %]; wave E [FE: 70.0±18.0 vs. MA: 73.0±14.0, cm/s]; wave A [FE: 20.0±12.0 vs. MA: 28.0±13.0, cm/s]; E/A [FE: 4.9±3.4 vs. MA: 3.3±1.8]) and sixth (FAC [FE: 29.0±7.0 vs. MA: 31.0±7.0, %]; wave E [FE: 85.0±18.0 vs. MA: 87.0±20.0, cm/s]; wave A [FE: 20.0±11.0 vs. MA: 28.0±17.0, cm/s]; E/A [FE: 6.2±4.0 vs. MA: 4.6±3.4]) week.

Conclusion

Gender does not influence left ventricle remodeling post-MI in rats.

Use of afterload hemodynamic stress as a practical method for assessing cardiac performance in rats with heart failure

After myocardial infarction, the hemodynamics under basal conditions might appear to be unaltered, which makes it difficult to identify cardiac dysfunction by the usual approaches. Thus, we tested the response to sudden afterload stress in infarcted rats with apparently normal ejection function. Control (CT) and infarcted (MI) Wistar rats with various MI sizes were submitted to echocardiography 30 days after coronary occlusion, followed by assessment of hemodynamics under basal conditions and during a pharmacologically induced sudden pressure overload (phenylephrine 15-25 microg/kg, i.v.). Coronary occlusion resulted in cardiac remodeling proportional to MI size, although several functional parameters such as systolic pressure (SP), stroke volume (SV), and stroke work (SW) of all MI rats were similar to those of CT rats. However, the afterload stress that was produced led to a relative preservation of SV and an increase of SW in CT rats; MI rats exhibited a significant reduction in SV and SW generation, although global cardiac function was normal under basal conditions, as indicated by regular echocardiography and hemodynamics assessment. Thus, we propose the use of sudden pharmacologically induced afterload stress as a practical and efficient procedure for identifying impaired performance of the heart in anesthetized rats, providing an additional physiological variable to be evaluated in experimental therapeutic studies.

Bone marrow cell therapy prevents infarct expansion and improves border zone remodeling after coronary occlusion in rats

BACKGROUND

Since the cell therapy benefits for myocardial infarction are mainly related to infarct reduction by regenerating lost myocardium or increasing survival of tissues at risk, we evaluated the effects of bone marrow-derived mononuclear cells (MNC), implanted after the completion of necrosis, on infarct progression and cardiac remodeling.

METHODS

After 48 h of induction of myocardial infarction (MI), Lewis-inbred rats were injected with 6 × 10(6) cells (MI+MNC) or saline (MI). After six weeks, scar dimension, ventricular morphology and function were analyzed by echocardiography followed by histomorphology of the infarcted and border zones.

RESULTS

After therapy, the relative size of the infarct was smaller in MI+MNC (37 ± 1% of the left ventricle) than in MI (43 ± 1%). While the MI group exhibited parallel elongation of the infarcted (31.6 ± 3.8% increase) and reminiscent ventricular portions (33.5 ± 3.7%), MNC therapy preserved the initial infarct length. Infarcted walls were thicker (979 ± 31 mm) in the MNC group than in the untreated group (709 ± 41 mm), also demonstrating an absence of infarct expansion. In the border zones, MNC led to increased capillary densities and capillary/myocyte ratios. The cardiac systolic function remained depressed in MI, but improved by 19 ± 5% in MI+MNC which reduced the incidence of pulmonary arterial hypertension (37.5% in MI and 6.25% in MI+MNC).

CONCLUSION

MNC therapy prevented the infarct expansion and thinning related to cardiac remodeling and was associated with an improvement of border zone microcirculation: as a result, MNC therapy reduced typical MI dysfunctional repercussions.

Hyperbaric oxygenation applied immediately after coronary occlusion reduces myocardial necrosis and acute mortality in rats

1. Because in ischaemia there is a critical lack of O2, it has been reasoned that increasing O2 delivery to the ischaemic myocardium could serve as adjunctive therapy for acute myocardial infarction (MI). Accordingly, in the present study, the effect of early hyperbaric oxygenation (HBO) on mortality and MI size after coronary occlusion was examined in rats. 2. After coronary occlusion, male Wistar rats were randomly assigned to receive either HBO for 1 h in a hyperbaric chamber (100% O(2) at 253 kPa; n = 106) or ambient O2 as the control (n = 111). The extent of myocardial necrosis was assessed (triphenyltetrazolium) immediately after treatment in the HBO (n = 50) and control (n = 47) groups. The remaining rats were evaluated 24 h after occlusion to enable calculation of MI size and mortality. 3. Immediately after therapy, the size of the MI was significantly greater in the control group compared with that in the HBO group (40 +/- 3 vs 27 +/- 2% of the left ventricle (LV), respectively; P < 0.001). The 24 h mortality of control rats was higher than that of HBO rats (34 vs 16%, respectively; P = 0.02). Control rats that survived 24 h had a larger MI than did HBO rats that survived 24 h (40 +/- 4 vs 29 +/- 3% of the LV, respectively; P = 0.005). Furthermore, large necrotic areas (> 40% of the LV) were more frequent in control than HBO rats (55 vs 27% of infarcted hearts, respectively; P = 0.01). There was less pulmonary congestion observed in HBO rats compared with control rats. 4. In conclusion, early therapy with HBO during the onset of an acute ischaemic event decreases the necrotic area and reduces acute mortality. These data support further investigation of HBO as an adjuvant therapy for acute MI.

An experimental rabbit model for off-pump left ventricular reconstruction following left ventricular aneurysm

BACKGROUND

Cardiac electromechanical remodeling following left ventricular reconstruction (LVR) surgery is not fully understood. Further development of an animal model will facilitate investigations in this area. In the present study, we aimed to establish a novel LVR procedure without the use of cardiopulmonary bypass in a rabbit left ventricular (LV) aneurysm model.

METHODS

LV aneurysm was created in 6 rabbits by ligation of the distal left coronary artery. More than a month later, LVR aneurysm surgery was performed off-pump using a purse-string suture around the aneurysm. Cardiac dimensions and function were evaluated using echocardiographic techniques perioperatively and 4 weeks after LVR surgery. Six structurally normal hearts were used as controls.

RESULTS

LVR surgery was successfully performed in all 6 rabbits. Both LV end-diastolic volume (LVEDV, 4.6 +/- 0.9 to 3.3 +/- 0.6 mL; P < .01) and LV end-systolic volume (LVESV, 2.5 +/- 0.6 to 1.5 +/- 0.2 mL, P < .01) were decreased immediately postsurgery versus presurgery, and LV ejection fraction (LVEF) was increased (44.5 +/- 5.3 to 55.6 +/- 4.8%, P < .001). For comparison, in normal rabbits (n = 6), LVEDV, LVESV and LVEF were 3.1 +/- 0.7 mL, 1.2 +/- 0.5 mL, and 64.5 +/- 8.8%, respectively. During follow-up, one rabbit died 3 weeks after surgery from an unknown cause. In the remaining 5 animals, improvements of LVEDV (3.7+/- 0.4 mL, P < .05), LVESV (1.7 +/- 0. 3 mL, P < .01), and LVEF (53.1 +/- 2.8%, P < .01) were maintained versus presurgery values for more than 4 weeks after LVR.

CONCLUSIONS

Off-pump LVR of rabbit LV aneurysm is an effective and less invasive surgery that resulted in sustained improvement in cardiac function with no gross intraoperative or postoperative mortality. This may be a useful model for investigations of electromechanical remodeling following LVR.

Performance of two-dimensional Doppler echocardiography for the assessment of infarct size and left ventricular function in rats

Although echocardiography has been used in rats, few studies have determined its efficacy for estimating myocardial infarct size. Our objective was to estimate the myocardial infarct size, and to evaluate anatomic and functional variables of the left ventricle. Myocardial infarction was produced in 43 female Wistar rats by ligature of the left coronary artery. Echocardiography was performed 5 weeks later to measure left ventricular diameter and transverse area (mean of 3 transverse planes), infarct size (percentage of the arc with infarct on 3 transverse planes), systolic function by the change in fractional area, and diastolic function by mitral inflow parameters. The histologic measurement of myocardial infarction size was similar to the echocardiographic method. Myocardial infarct size ranged from 4.8 to 66.6% when determined by histology and from 5 to 69.8% when determined by echocardiography, with good correlation (r = 0.88; P < 0.05; Pearson correlation coefficient). Left ventricular diameter and mean diastolic transverse area correlated with myocardial infarct size by histology (r = 0.57 and r = 0.78; P < 0.0005). The fractional area change ranged from 28.5 +/- 5.6 (large-size myocardial infarction) to 53.1 +/- 1.5% (control) and correlated with myocardial infarct size by echocardiography (r = -0.87; P < 0.00001) and histology (r = -0.78; P < 00001). The E/A wave ratio of mitral inflow velocity for animals with large-size myocardial infarction (5.6 +/- 2.7) was significantly higher than for all others (control: 1.9 +/- 0.1; small-size myocardial infarction: 1.9 +/- 0.4; moderate-size myocardial infarction: 2.8 +/- 2.3). There was good agreement between echocardiographic and histologic estimates of myocardial infarct size in rats.

Immediate Functional Effects of Left Ventricular Reduction: A Doppler Echocardiographic Study in the Rat

BACKGROUND

Immediate functional effects of left ventricle reduction (LVR) are not yet fully defined. Those effects have been studied in the experimental model of myocardial infarction scar plication (MISP) in the rat.

METHODS AND RESULTS

A Doppler echocardiogram was performed immediately before and after MISP in 20 rats with infarction of the left ventricle (LV) larger than 40%. LV diastolic volume reduction (475 +/- 114 versus 185 +/- 65 muL) was accompanied by heart rate decrease (230 +/- 25 versus 166 +/- 27 beats/min) and increase of ejection fraction (37 +/- 7 versus 67 +/- 12%), fractional shortening (18 +/- 3 versus 46 +/- 8%) and posterior wall shortening velocity (1.50 +/- 0.62 versus 2.01 +/- 0.46 cm/s). LV diastolic volume/stroke volume slope was steeper after LVR, suggesting enhancement of the Frank-Starling mechanism. Restrictive pattern of left atrial emptying was alleviated after LVR (E wave: 101 +/- 15 versus 66 +/- 14 cm/s; E/A ratio: 6.8 +/- 2.9 versus 5.0 +/- 2.2; E wave deceleration time: 36 +/- 6 versus 51 +/- 10 msec) even though left atrial diameter (0.69 +/- 0.07 versus 0.66 +/- 0.06 cm) and A wave (18.0 +/- 9.4 versus 15.8 +/- 7.8 cm/s) did not vary. Additionally, a pulmonary flow profile suggesting pulmonary hypertension was observed in 12 of 17 animals before, and in only 3 after, LVR.

CONCLUSION

LVR favors cardiac function not only by reducing afterload. The present data are in consonance with previous suggestions that the Frank-Starling mechanism is enhanced after MISP and, in addition to LV ejection function improvement, the unprecedented facilitation of left atrial emptying after LVR was particularly noteworthy. Even though LVR restricts ventricular distensibility, atrial emptying can be facilitated, probably on account of LV ejection improvement.

Atrial Natriuretic Peptide Helps Prevent Late Remodeling After Left Ventricular Aneurysm Repair

BACKGROUND

Left ventricular aneurysm repair (LVR) reduces LV wall stress and improves LV function. However, as we reported previously, the initial improvement of LVR was short-term because of LV remodeling but could be maintained longer with postoperative use of an angiotensin-converting enzyme (ACE) inhibitor. Atrial natriuretic peptide (ANP) has been used to treat patients with heart failure by natriuretic and vasodilatory actions. Recent reports have suggested that ANP inhibits the rennin-angiotensin system. In this study, the effects of ANP after LVR were evaluated.

METHODS AND RESULTS

Rats that had an LV aneurysm 4 weeks after left anterior descending artery ligation underwent LVR by plicating the LV aneurysm and were randomized into 2 groups: LVR+A group was intravenously administrated with 10 microg/h of carperitide, recombinant alpha-hANP, by osmotic-pump for 4 weeks, and the LVR group was given normal saline. Echocardiography revealed better LV remodeling and function in LVR+A group than in LVR group. Four weeks after LVR, left ventricular end diastolic pressure (LVEDP) and Tau were significantly lower in LVR+A group (LVEDP: 10+/-4 in LVR+A group versus 18+/-6 mm Hg in LVR group, Tau: 13+/-2 versus 17+/-2ms). End-systolic elastance (Ees) was higher in LVR+A group (Ees: 0.34+/-0.2 versus 0.19+/-0.11 mm Hg/microL). The levels of myocardial ACE activity in LVR+A group was significantly lower than in LVR group. The mRNA expressions of brain natriuretic peptide and transforming growth factor beta1 inducing fibrosis significantly decreased in LV myocardium in LVR+A group. Histologically, myocardial fibrosis was significantly reduced in LVR+A group.

CONCLUSIONS

Intravenous administration of ANP had beneficial effects on LV remodeling, function, and fibrosis after LVR. ANP could be a useful intravenous infusion drug for postoperative management after LV repair surgery.