Evaluation of cardiac arrhythmic risks using a rabbit model of left ventricular systolic dysfunction

A novel method for the percutaneous induction of myocardial infarction by occlusion of small coronary arteries in the rabbit

Arrhythmic sudden cardiac death (SCD) is an important cause of mortality following myocardial infarction (MI). The rabbit has similar cardiac electrophysiology to humans and is therefore an important small animal model to study post-MI arrhythmias. The established approach of surgical coronary ligation results in thoracic adhesions that impede epicardial electrophysiological studies. Adhesions are absent following a percutaneously induced MI, which is also associated with reduced surgical morbidity and so represents a clear refinement of the approach. Percutaneous procedures have previously been described in large rabbits (3.5-5.5 kg). Here, we describe a novel method of percutaneous MI induction in smaller rabbits (2.5-3.5 kg) that are readily available commercially. New Zealand White rabbits (n = 51 males, 3.1 ± 0.3 kg) were anesthetized using isoflurane (1.5-3%) and underwent either a percutaneous MI procedure involving microcatheter tip deployment (≤1.5 Fr, 5 mm), coronary ligation surgery, or a sham procedure. Electrocardiography (ECG) recordings were used to confirm ST-segment elevation indicating coronary occlusion. Blood samples (1 and 24 h) were taken for cardiac troponin I (cTnI) levels. Ejection fraction (EF) was measured at 6-8 wk. Rabbits were then euthanized (Euthatal) and hearts were processed for magnetic resonance imaging and histology. Mortality rates were similar in both groups. Scar volume, cTnI, and EF were similar between both MI groups and significantly different from their respective sham controls. Thus, percutaneous coronary occlusion by microcatheter tip deployment is feasible in rabbits (2.5-3.5 kg) and produces an MI with similar characteristics to surgical ligation with lower procedural trauma and without epicardial adhesions.NEW & NOTEWORTHY Surgical coronary ligation is the standard technique to induce myocardial infarction (MI) in rabbits but is associated with procedural trauma and the generation of thoracic adhesions. Percutaneous coronary occlusion avoids these shortcomings and is established in pigs but has only been applicable to large rabbits because of a mismatch between the equipment used and target vessel size. Here, we describe a new scalable approach to percutaneous MI induction that is safe and effective in 2.5-3.5-kg rabbits.

Relationship Between Vitamin D Level and Index of CardioElectrophysiological Balance in Children

BACKGROUND

Vitamin D deficiency has been found to be associated with various cardiovascular disorders, including hypertension, coronary artery disease, heart failure, peripheral vascular diseases, and sudden cardiac death. In the literature, it has been reported that many electrocardiographic parameters have been developed to predict ventricular arrhythmias. In recent studies, it is noteworthy that the index of cardio-electrophysiological balance (iCEB) and correct cardioelectrophysiological balance (iCEBc), which are electrocardiographic parameters, can be used as new, easy, cheap and non-invasive parameters to predict ventricular arrhythmias.

OBJECTIVE

This study aimed to investigate the relationship between vitamin D deficiency and iCEB and iCEBc values in children.

METHODS

A total of 186 patients were included in this study. Group 1 included 114 patients with vitamin D levels below 20 ng/ml; 50 patients with vitamin D levels of 21-29 ng/ml were included in Group 2; Group 3 consisted of 36 patients with a vitamin D level above 30 ng/ml. iCEB and iCEBc values were calculated by taking 12-lead ECG from all individuals and comparing them between groups.

RESULTS

A total of 186 children, 114 subjects in Group 1, 36 subjects in Group 2, and 36 subjects in Group 3, were included in the study. Demographic characteristics and height-weight values of the groups were similar. Significant differences were found between the groups in terms of QT, QTc, QT/QRS, and QTc/QRS levels (p: 0.003, 0.028, 0.001, and 0.001, respectively). In the correlation analysis, a negative correlation was found between QTc/QRS and vitamin D level (r=-0.320, p=<0.001) and between QT/QRS and vitamin D level (r=-0.268, p=<0.001). Moreover, vitamin D level (β=0.389, p<0.001) was determined as an independent predictor of QTc/QRS in multivariate logistic regression analysis.

CONCLUSION

iCEB and iCEBc parameters increase significantly in children with low vitamin D levels. These parameters are also evaluated during the follow-up of children with vitamin D deficiency in terms of the risk of ventricular arrhythmia. iCEBc can be used as an easy, inexpensive, non-invasive, and reproducible parameter.

Biological Activity of a 4-Hydroxy-Furanyl-Benzamide Derivative on Heart Failure

BACKGROUND

There are studies that suggest that some benzamide derivatives may exert effects on heart failure; however, their molecular mechanism is not very clear.

OBJECTIVE

The aim of this research was to evaluate the biological activity of a 4-hydroxy-furanyl-benzamide derivative against heart failure translated as area infarct.

METHODS

Biological activity produced by 4-hydroxy-furanyl-benzamide derivative against heart failure was determinate using an ischemia-reperfusion injury model. In addition, the effects exerted by the 4-hydroxy-furanyl-benzamide derivative on left ventricular pressure (LVP) was evaluated in the absence or presence of some drugs such as yohimbine, butaxamine, methoctramine and L-NAME using a model of rat heart isolated.

RESULTS

The results showed that 4-hydroxy-furanyl-benzamide derivative decrease both infarct area and LVP. However, the effect produced by 4-hydroxy-furanyl-benzamide derivative on LVP was inhibited in the presence of both methoctramine and L-NAME.

CONCLUSIONS

All these data suggest that biological activity produced by 4-hydroxy-furanyl-benzamide derivative on left ventricular pressure is through of both M₂-muscarinic receptor and nitric oxide synthase enzyme activation. It is important to mention that this phenomenon results as a decrease of both infarct area and heart failure.

The Feasibility and Safety of Flecainide Use Among Patients With Varying Degrees of Coronary Disease

BACKGROUND

Class 1C antiarrhythmic agents are effective for treating atrial tachyarrhythmias, but their use is restricted in patients with coronary artery disease (CAD). Data on the safety of the use of 1C agents in patients with CAD in the absence of recent acute coronary syndromes are lacking.

OBJECTIVE

This study sought to evaluate the safety and feasibility of treatment with 1C agents in patients with varying degrees of CAD in a large serial, real-world cohort.

METHODS

We retrospectively identified all patients at our institution from January 2005 to February 2021 on a 1C agent (n = 3,445) and those on sotalol or dofetilide (n = 2,216) as controls, excluding those with a prior history of ventricular tachycardia, implantable cardioverter-defibrillator placement, or nonrevascularized myocardial infarction. Baseline clinical characteristics included degree of CAD (categorized as none, nonobstructive, or obstructive), other comorbid illness, and medication use. Clinical outcomes, including survival, were ascertained. We performed Cox regression analysis to evaluate the effect of 1C use on event-free survival across varying degrees of CAD.

RESULTS

After adjustment for baseline characteristics, there was an independent association between 1C use and improved mortality. However, there was an interaction between 1C use and degree of CAD (compared to sotalol) demonstrating poorer event-free survival among those with obstructive coronary disease (HR: 3.80; 95% CI: 1.67-8.67; P = 0.002).

CONCLUSIONS

Among select patients with nonobstructive CAD and without a history of ventricular tachycardia, 1C agents are not associated with increased mortality. Therefore, these agents may be an option for some patients in whom they are frequently restricted. Further prospective studies are warranted.

Prognostic value of index of cardiac electrophysiological balance among US middle-aged adults

Background

Index of cardiac electrophysiological balance (iCEB) has been widely used in clinical practice but no studies investigated the association between iCEB and prognosis in the general population.

Objective

To assess the correlation between the iCEB and the prognosis in the general population.

Methods

This retrospective cohort study involved adults aged 40-65 years who participated in the Third National Health and Nutrition Examination Survey (NHANES-III) and whose electrocardiograms were in sinus rhythm. The corrected iCEB (iCEBc) was the ratio of corrected QT interval (QTc) to QRS duration, and outcomes were cardiac and all-cause mortality. Cox proportional hazards regression model was used to identify the associations of iCEBc with end point. The value of iCEBc for predicting adverse events was evaluated by reclassification and discrimination analyses.

Results

Among 5,010 participants (mean age 51.10 ± 7.67 years, 52.5% female), 3,454 (68.9%) were Non-Hispanic White. The mean iCEBc was 4.45 ± 0.56. A total of 2,147 deaths were recorded during a median follow-up of 319 months. The adjusted model shown iCEBc was an independent risk factor for all-cause death. The iCEBc was linearly correlated with all-cause mortality and the optimal cutoff value was 4.57 in males and 4.98 in females. In the resultant model, prolonged iCEBc remained independently associated with a higher rate of mortality (HR: 1.25; 95% CI: 1.11-1.42) and cardiac death (HR: 1.34; 95% CI: 1.04-1.71). Among the complete study population or the group with normal QTc interval, the performance of the predictive model after addition of iCEBc was not weaker than the model after the addition of prolonged QTc.

Conclusion

Elevated iCEBc (male ≥4.57 and female ≥4.98) is an independent risk factor for cardiac or all-cause death among the middle-age adults. The clinical application value of iCEBc is firmly based on basic physiological principles and its application deserves further attention.

Long-term outcomes in patients treated with flecainide for atrial fibrillation with stable coronary artery disease

BACKGROUND

Class 1C antiarrhythmic drugs (AAD) have been associated with harm in patients treated for ventricular arrhythmias with a prior myocardial infarction. Consensus guidelines have advocated that these drugs not be used in patients with stable coronary artery disease (CAD). However, long-term data are lacking to know if unique risks exist when these drugs are used for atrial fibrillation (AF) in patients with CAD without a prior myocardial infarction.

METHODS

In 24,315 patients treated with the initiation of AADs, two populations were evaluated: (1) propensity-matched AF patients with CAD were created based upon AAD class (flecainide, n = 1,114, vs class-3 AAD, n = 1,114) and (2) AF patients who had undergone a percutaneous coronary intervention or coronary artery bypass graft (flecainide, n = 150, and class-3 AAD, n = 1,453). Outcomes at 3 years for mortality, heart failure (HF) hospitalization, ventricular tachycardia (VT), and MACE were compared between the groups.

RESULTS

At 3 years, mortality (9.1% vs 19.3%, P < .0001), HF hospitalization (12.5% vs 18.3%, P < .0001), MACE (22.9% vs 36.6%, P < .0001), and VT (5.8% vs 8.5%, P = .02) rates were significantly lower in the flecainide group for population 1. In population 2, adverse event rates were also lower, although not significantly, in the flecainide compared to the class-3 AAD group for mortality (20.9% vs 25.8%, P = .26), HF hospitalization (24.5% vs 26.1%, P = .73), VT (10.9% vs 14.7%, P = .28) and MACE (44.5% vs 49.5%, P = .32).

CONCLUSIONS

Flecainide in select patients with stable CAD for AF has a favorable safety profile compared to class-3 AADs. These data suggest the need for prospective trials of flecainide in AF patients with CAD to determine if the current guideline-recommended exclusion is warranted.

Absent or Mild Coronary Calcium Predicts Low-Risk Stress Test Results and Outcomes in Patients Considered for Flecainide Therapy

BACKGROUND

Flecainide is a useful antiarrhythmic for atrial fibrillation (AF). However, because of ventricular proarrhythmia risk, a history of myocardial infarction (MI) or coronary artery disease (CAD) is a flecainide exclusion, and stress testing is used to exclude ischemia. We assessed whether absent/mild coronary artery calcium (CAC) can supplement or avoid the need for stress testing.

METHODS

We assessed ischemic burden using regadenoson Rb-82 PET/CT in 1372 AF patients ≥50 years old without symptoms or signs of clinical CAD. CAC was determined qualitatively by low dose attenuation computed tomography (CT) (n = 816) or by quantitative CT (n = 556). Ischemic burden and clinical outcomes were compared by CAC burden.

RESULTS

Patients with CAC absent or mild (n = 766, 57.2%) were younger, more frequently female, and had higher BMI but lower rates of diabetes, hypertension, and dyslipidemia. Average ischemic burden was lower in CAC-absent/mild patients, and CAC-absent/mild patients showed greater coronary flow reserve, had fewer referrals for coronary angiography, and less often had obstructive CAD. Revascularization at 90 days was lower, and the rate of longer-term major adverse cardiovascular events was favorable.

CONCLUSIONS

An easily administered, inexpensive, low radiation CAC scan can identify a subset of flecainide candidates with a low ischemic burden on PET stress testing that rarely needs coronary angiography/intervention and has favorable outcomes. Absent or mild CAC-burden combined with other clinical information may avoid or complement routine stress testing. However, additional, ideally randomized and multicenter trials are indicated to confirm these findings before replacing stress testing with CAC screening in selecting patients for flecainide therapy in clinical practice.

Cardiac contractility modulation attenuates structural and electrical remodeling in a chronic heart failure rabbit model

Background

Cardiac contractility modulation (CCM) is non-excitatory electrical stimulation for improving cardiac function. This study aimed to evaluate the effects of CCM on structural and electrical remodeling in a rabbit model of chronic heart failure (CHF).

Methods

Thirty rabbits were randomly divided into the sham, CHF, and CCM groups. The CHF model was induced 12 weeks after trans-aortic constriction by pressure unloading and CCM was delivered to the myocardium for 4 weeks. Corrected QT intervals, the ventricular effective refractory period, and inducibility of ventricular tachycardia were measured by an electrophysiological examination. Connective tissue growth factor, galectin-3, Kv4.3, KCNQ1, KCNH2, and connexin 43 protein levels were measured by western blotting.

Results

The CHF group had a significantly prolonged corrected QT interval and ventricular effective refractory period, and increased inducibility of ventricular tachycardia. Prominent myocardial fibrosis and increased hydroxyproline content were observed in the CHF group, but these were suppressed in the CCM group. Kv4.3, KCNQ1, KCNH2, and connexin 43 protein levels were significantly lower in the CHF group, but treatment with CCM partially restored their levels.

Conclusions

CCM attenuates myocardial structural and electrical remodeling during CHF. These findings provide evidence for clinical use of CCM in treating CHF.

ECG Arrhythmia Classification using High Order Spectrum and 2D Graph Fourier Transform

Heart diseases are in the front rank among several kinds of life threats, due to its high incidence and mortality. Regarded as a powerful tool in the diagnosis of the cardiac disorder and arrhythmia detection, analysis of electrocardiogram (ECG) signals has become the focus of numerous researches. In this study, a feature extraction method based on the bispectrum and 2D graph Fourier transform (GFT) was developed. High-order matrix founded on bispectrum are extended into structured datasets and transformed into the eigenvalue spectrum domain by GFT, so that features can be extracted from statistical quantities of eigenvalues. Spectral features have been computed to construct the feature vector. Support vector machine based on the radial basis function kernel (SVM-RBF) was used to classify different arrhythmia heartbeats downloaded from the Massachusetts Institute of Technology - Beth Israel Hospital (MIT-BIH) Arrhythmia Database, according to the Association for the Advancement of Medical Instrumentation (AAMI) standard. Based on the cross-validation method, the experimental results depicted that our proposed model, the combination of bispectrum and 2D-GFT, achieved a high classification accuracy of 96.2%.

Monitoring reperfused myocardial infarction with delayed left ventricular systolic dysfunction in rabbits by longitudinal imaging

Background

An experimental imaging platform for longitudinal monitoring and evaluation of cardiac morphology-function changes has been long desired. We sought to establish such a platform by using a rabbit model of reperfused myocardial infarction (MI) that develops chronic left ventricle systolic dysfunction (LVSD) within 7 weeks.

Methods

Fifty-five New Zeeland white (NZW) rabbits received sham-operated or 60-min left circumflex coronary artery (LCx) ligation followed by reperfusion. Cardiac magnetic resonance imaging (cMRI), transthoracic echocardiography (echo), and blood samples were collected at baseline, in acute (48 hours or 1 week) and chronic (7 weeks) stage subsequent to MI for in vivo assessment of infarct size, cardiac morphology, LV function, and myocardial enzymes. Seven weeks post MI, animals were sacrificed and heart tissues were processed for histopathological staining.

Results

The success rate of surgical operation was 87.27%. The animal mortality rates were 12.7% and 3.6% both in acute and chronic stage separately. Serum levels of the myocardial enzyme cardiac Troponin T (cTnT) were significantly increased in MI rabbits as compared with sham animals after 4 hours of operation (P<0.05). According to cardiac morphology and function changes, 4 groups could be distinguished: sham rabbits (n=12), and MI rabbits with no (MI_NO_LVSD; n=10), moderate (MI_M_LVSD; n=9) and severe (MI_S_LVSD; n=15) LVSD. No significant differences in cardiac function or wall thickening between sham and MI_NO_LVSD rabbits were observed at both stages using both cMRI and echo methods. cMRI data showed that MI_M_LVSD rabbits exhibited a reduction of ejection fraction (EF) and an increase in end-systolic volume (ESV) at the acute phase, while at the chronic stage these parameters did not change further. Moreover, in MI_S_LVSD animals, these observations were more striking at the acute stage followed by a further decline in EF and increase in ESV at the chronic stage. Lateral wall thickening determined by cMRI was significantly decreased in MI_M_LVSD versus MI_NO_LVSD animals at both stages (P<0.05). As for MI_S_LVSD versus MI_M_LVSD rabbits, the thickening of anterior, inferior and lateral walls was significantly more decreased at both stages (P<0.05). Echo confirmed the findings of cMRI. Furthermore, these in vivo outcomes including those from vivid cine cMRI could be supported by exactly matched ex vivo histomorphological evidences.

Conclusions

Our findings indicate that chronic LVSD developed over time after surgery-induced MI in rabbits can be longitudinally evaluated using non-invasive imaging techniques and confirmed by the entire-heart-slice histomorphology. This experimental LVSD platform in rabbits may interest researchers in the field of experimental cardiology and help strengthen drug development and translational research for the management of cardiovascular diseases.