Heart Rate Reduction With Ivabradine Protects Against Left Ventricular Remodeling by Attenuating Infarct Expansion and Preserving Remote-Zone Contractile Function and Synchrony in a Mouse Model of Reperfused Myocardial Infarction

Hyperpolarization-activated cyclic nucleotide-gated channel inhibitor in myocardial infarction: Potential benefits beyond heart rate modulation

Myocardial infarction (MI) and its associated complications including ventricular arrhythmias and heart failure are responsible for a significant incidence of morbidity and mortality worldwide. The ensuing cardiomyocyte loss results in neurohormone-driven cardiac remodeling, which leads to chronic heart failure in MI survivors. Ivabradine is a heart rate modulation agent currently used in treatment of chronic heart failure with reduced ejection fraction. The canonical target of ivabradine is the hyperpolarization-activated cyclic nucleotide-gated channels (HCN) in cardiac pacemaker cells. However, in post-MI hearts, HCN can also be expressed ectopically in non-pacemaker cardiomyocytes. There is an accumulation of intriguing evidence to suggest that ivabradine also possesses cardioprotective effects that are independent of heart rate reduction. This review aims to summarize and discuss the reported cardioprotective mechanisms of ivabradine beyond heart rate modulation in myocardial infarction through various molecular mechanisms including the prevention of reactive oxygen species-induced mitochondrial damage, improvement of autophagy system, modulation of intracellular calcium cycling, modification of ventricular electrophysiology, and regulation of matrix metalloproteinases.

PR Interval as a Novel Therapeutic Target of Ivabradine Therapy-Prognostic Impact of Ivabradine-Induced PR Prolongation in Heart Failure Patients

BACKGROUND

Ivabradine reduces heart rate by inhibiting the "funny current" expressed on the sinoatrial node and improves mortality and morbidity in patients with systolic heart failure and sinus tachycardia. The funny current is known to be expressed also on the atrioventricular node according to experimental studies. However, the impact of ivabradine on PR interval remained unknown.

METHODS

Patients with a left ventricular ejection fraction of less than 50% who received 1 month of ivabradine were screened. Electrocardiographic and echocardiographic data, particularly concerning heart rate, the PR interval, and trans-mitral flow pattern, were collected at baseline and 1-month follow-up. The primary endpoint was defined as the composite of cardiovascular death and hospital readmission for worsening heart failure following ivabradine administration.

RESULTS

In the cohort of 29 enrolled patients (median age: 66 years, 62% male), the median baseline heart rate was 86 beats per minute and the median PR interval was 168 milliseconds. Following ivabradine administration, a significant decrease of 20 beats per minute in the heart rate and a significant increase of 24 milliseconds in the PR interval were observed. The truncated interval of the A-wave, detected in the trans-mitral flow, consistently demonstrated a negative correlation with the PR interval both before and after the administration of ivabradine. During a median of 1.8 years of follow-up, six patients reached the primary endpoint. A combination of heart rate reduction and PR prolongation following ivabradine administration, both of which were independent factors associated with the primary endpoint (p < 0.05 for both), was associated with greater freedom from the primary endpoint compared with either/neither of them (p = 0.002).

CONCLUSIONS

Ivabradine seems to prolong PR interval, which is a novel surrogate marker of favorable clinical outcomes in patients with systolic heart failure. This effect may be associated with the dynamics of the trans-mitral flow pattern, in conjunction with heart rate and the PR interval. Clinical implications of PR interval-guided ivabradine therapy remains the future concern.

The impact of medical therapy on left ventricular strain: Current state and future perspectives

The speckle tracking strain is becoming a frequently used marker of subclinical left ventricular systolic dysfunction. Despite the wide range of data concerning left ventricular strain variability in the general population and its changes in various pathologic conditions, the information about the impact of medical therapy on left ventricle strain is limited. This article provides an analysis of published studies of left ventricle strain changes in response to different agents and combinations of medical therapies used for hypertension and congestive heart failure.

Biomedical Imaging in Experimental Models of Cardiovascular Disease

Major advances in biomedical imaging have occurred over the last 2 decades and now allow many physiological, cellular, and molecular processes to be imaged noninvasively in small animal models of cardiovascular disease. Many of these techniques can be also used in humans, providing pathophysiological context and helping to define the clinical relevance of the model. Ultrasound remains the most widely used approach, and dedicated high-frequency systems can obtain extremely detailed images in mice. Likewise, dedicated small animal tomographic systems have been developed for magnetic resonance, positron emission tomography, fluorescence imaging, and computed tomography in mice. In this article, we review the use of ultrasound and positron emission tomography in small animal models, as well as emerging contrast mechanisms in magnetic resonance such as diffusion tensor imaging, hyperpolarized magnetic resonance, chemical exchange saturation transfer imaging, magnetic resonance elastography and strain, arterial spin labeling, and molecular imaging.

Effect of early use of ivabradine on left ventricular remodeling after primary percutaneous coronary intervention in patients with acute ST-segment elevation myocardial infarction: A pilot test

Objective

To investigate the effect of early use of ivabradine on left ventricular remodeling after primary percutaneous coronary intervention (PCI) in patients with acute ST‐segment elevation myocardial infarction (STEMI).

Methods

A total of 66 STEMI patients with sinus rhythm and the resting heart rate ≥80 bpm after successful emergency PCI were included. The patients in the test group were treated with ivabradine combined with metoprolol at 12 hr after PCI, while the control group was given only metoprolol orally. Their resting heart rate was controlled to <70 bpm at discharge and followed for 180 days. Heart rate and blood pressure were measured regularly. Echocardiogram was performed. N‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP), high sensitivity troponin T, high sensitivity troponin I, and high sensitivity C‐reactive protein were measured. The major adverse cardiovascular events during hospitalization and follow‐up period were recorded.

Results

Compared with the control group, the heart rate of the test group decreased significantly (p < .05). Compared with the control group, the left ventricular end‐diastolic volume and left ventricular end‐systolic volume were significantly decreased while left ventricular ejection fraction was significantly increased in the test group at 90 days after operation. NT‐proBNP of the test group was significantly lower than that of the control group at 7 days after operation (p < .05).

Conclusion

For STEMI patients, early use of ivabradine combined with standard therapy such as β‐blocker after successful reperfusion can achieve effective heart rate control, with great safety and tolerance. But the effect of ivabradine on left ventricular remodeling is uncertain.

Functional and prognostic implications of cardiac magnetic resonance feature tracking-derived remote myocardial strain analyses in patients following acute myocardial infarction

Background

Cardiac magnetic resonance myocardial feature tracking (CMR-FT)-derived global strain assessments provide incremental prognostic information in patients following acute myocardial infarction (AMI). Functional analyses of the remote myocardium (RM) are scarce and whether they provide an additional prognostic value in these patients is unknown.

Methods

1034 patients following acute myocardial infarction were included. CMR imaging and strain analyses as well as infarct size quantification were performed after reperfusion by primary percutaneous coronary intervention. The occurrence of major adverse cardiac events (MACE) within 12 months after the index event was defined as primary clinical endpoint.

Results

Patients with MACE had significantly lower RM circumferential strain (CS) compared to those without MACE. A cutoff value for RM CS of − 25.8% best identified high-risk patients (p < 0.001 on log-rank testing) and impaired RM CS was a strong predictor of MACE (HR 1.05, 95% CI 1.07–1.14, p = 0.003). RM CS provided further risk stratification among patients considered at risk according to established CMR parameters for (1) patients with reduced left ventricular ejection fraction (LVEF) ≤ 35% (p = 0.038 on log-rank testing), (2) patients with reduced global circumferential strain (GCS) > −  18.3% (p = 0.015 on log-rank testing), and (3) patients with large microvascular obstruction ≥ 1.46% (p = 0.002 on log-rank testing).

Conclusion

CMR-FT-derived RM CS is a useful parameter to characterize the response of the remote myocardium and allows improved stratification following AMI beyond commonly used parameters, especially of high-risk patients.

Trial registration

ClinicalTrials.gov, NCT00712101 and NCT01612312

Graphic abstract

Defining remote segments (R) in the presence of infarct areas (I) for the analysis of remote circumferential strain (CS). Remote CS was significantly lower in patients who suffered major adverse cardiac events (MACE) and a cutoff value for remote CS of − 25.8% best identified high-risk patients. In addition, impaired remote CS ≥ − 25.8 % (Remote −) and preserved remote CS < − 25.8 % (Remote +) enabled further risk stratification when added to established parameters like left ventricular ejection fraction (LVEF), global circumferential strain (GCS) or microvascular obstruction (MVO).

Ivabradine promotes angiogenesis and reduces cardiac hypertrophy in mice with myocardial infarction

OBJECTIVE

We investigated the underlying mechanism of ivabradine (IVA) in promoting angiogenesis and reducing cardiac hypertrophy in mice with myocardial infarction (MI).

METHODS

Nineteen mice were randomly assigned into three groups as follows: sham group (10 ml/kg/day phosphate buffer saline (PBS), n=6), model group (MI and 10 ml/kg/day PBS, n=6) and IVA group (MI and 10 mg/kg/day IVA, n=7). All groups received an intragastric gavage for four weeks. Heart and body mass were measured. Cardiac function and heart rate were assessed by echocardiography and electrocardiography, respectively. The collagen deposition, area of cardiomyocytes, and number of capillaries were evaluated using Masson's staining, anti-wheat germ agglutinin (WGA) staining, and platelet endothelial cell adhesion molecule-1 (CD31) staining, respectively. The protein kinase B (Akt)- endothelial nitric oxide synthase (eNOS) signaling and p-38 mitogen-activated protein kinase (MAPK) family in myocardium were determined by western blot.

RESULTS

IVA treatment greatly improved cardiac dysfunction and suppressed cardiac hypertrophy at 4 weeks after MI (p<0.05). Heart rate and fibrotic area of IVA group declined notably compared to those of the model group (p<0.05). IVA administration substantially reduced cardiomyocyte size and increased capillary formation (p<0.05). Besides, IVA medication can enhance Akt-eNOS signaling and inhibit p38 MAPK phosphorylation in the heart of mice with MI (p<0.05).

CONCLUSION

IVA can perform two functions, the promotion of angiogenesis and the reduction of cardiac hypertrophy, both of which were closely associated with Akt-eNOS signaling activation and p38 MAPK inhibition.

Use of Multifactorial Treatments to Address the Challenge of Translating Experimental Myocardial Infarct Reduction Strategies

Myocardial tissue damage that occurs during an ischemic event leads to a spiraling deterioration of cardiac muscle structural and functional integrity. Reperfusion is the only known efficacious strategy and is the most commonly used treatment to reduce injury and prevent remodeling. However, timing is critical, and the procedure is not always feasible for a variety of reasons. The complex molecular basis for cardioprotection has been studied for decades but formulation of a viable therapeutic that can significantly attenuate myocardial injury remains elusive. In this review, we address barriers to the development of a fruitful approach that will substantially improve the prognosis of those suffering from this widespread and largely unmitigated disease. Furthermore, we proffer that ephrinA1, a candidate molecule that satisfies many of the important criteria discussed, possesses robust potential to overcome these hurdles and thus offers protection that surpasses the limitations currently observed.

A novel echocardiographic method closely agrees with cardiac magnetic resonance in the assessment of left ventricular function in infarcted mice

Cardiac Magnetic Resonance (CMR) is the gold standard for left ventricular (LV) function assessment in small rodents and, though echocardiography (ECHO) has been proposed as an alternative method, LV volumes may be underestimated when marked eccentric remodeling is present. In the present study we described a novel echocardiographic method and we tested the agreement with CMR for LV volumes and ejection fraction calculation in mice with experimental myocardial infarction. Sham-operated and infarcted mice, subjected to Coronary Artery Ligation, underwent ECHO and CMR. Volumes and ejection fraction were calculated by ECHO using a standard Simpson’s modified method (ECHO pLAX) or a method from sequential parasternal short axis (ECHO pSAX) acquired mechanically by translating the probe every 1 mm along the left ventricle. The mean differences ±1.96 standard deviation near to zero suggested close agreement between ECHO pSAX and CMR; contrarily ECHO pLAX agreement with CMR was lower. In addition, ECHO was three times shorter and cheaper (Relative cost difference: pLAX: −66% and pSAX −57%) than CMR. In conclusion, ECHO pSAX is a new, fast, cheap and accurate method for LV function assessment in mice.

Myocardial perfusion imaging detects mechanical dyssynchrony in left ventricular infarcted and noninfarcted areas early after acute myocardial infarction in a porcine model

BACKGROUND

Left ventricular mechanical dyssynchrony (LVMD) is closely associated with left ventricular dysfunction and poor prognosis in patients with acute myocardial infarction (AMI). However, whether mechanical dyssynchrony is present in the noninfarcted areas remains controversial. This research aimed to quantitatively evaluate the global and regional mechanical dyssynchrony early after AMI by phase analysis of single-photon emission computed tomography (SPECT) gated myocardial perfusion imaging (GMPI) and to further explore the related influencing factors.

MATERIALS AND METHODS

Of 11 Bama suckling pigs, eight animals were successfully subjected to left anterior descending artery occlusion by balloon to generate porcine AMI models and completed the study. SPECT GMPI was performed before AMI and at 1 day, 1 week, and 4 weeks after AMI. The global bandwidth (BW), SD, entropy, total perfusion deficit, summed rest score, regional BW, regional summed motion score, and regional summed thickening score were measured by SPECT GMPI.

RESULTS

The global BW, SD, and entropy values significantly increased after AMI and showed no significant change among the three time points after AMI. The BW in the infarcted area (left anterior descending artery-dominated area) at 1 day, 1 week, and 4 weeks after AMI was significantly higher than that before AMI, as was the BW in the noninfarcted areas (left circumflex artery-dominated and right coronary artery-dominated areas), which revealed that there was less dyssynchrony in the noninfarcted areas than in the infarcted area at the three time points after AMI. The global BW was positively correlated with the scar burden measured by summed rest score (r=0.709-0.832, all P<0.05), whereas the regional BW in the noninfarcted areas after AMI showed moderate to good correlation with regional summed motion score (r=0.733-0.875, all P<0.05) and regional summed thickening score (r=0.713-0.889, all P<0.05).

CONCLUSION

LVMD occurs early on the first day after AMI, with no significant worsening over the next 4 weeks. Mechanical dyssynchrony was present in both the infarcted and noninfarcted areas. The global LVMD is mainly influenced by the scar burden, and the regional mechanical dyssynchrony in the noninfarcted areas is closely associated with the abnormal regional wall thickening and motion, which are indicative of reduced myocardial contractility.