Missing Link between Molecular Aspects of Ventricular Arrhythmias and QRS Complex Morphology in Left Ventricular Hypertrophy

Distinct Cardiac Connexin-43 Expression in Hypertrophied and Atrophied Myocardium May Impact the Vulnerability of the Heart to Malignant Arrhythmias. A Pilot Study

Our and other studies suggest that myocardial hypertrophy in response to hypertension and hyperthyroidism increases propensity of the heart to malignant arrhythmias, while these are rare in conditions of hypothyroidism or type-1 diabetes mellitus associated with myocardial atrophy. One of the crucial factors impacting the susceptibility of the heart to life-threatening arrhythmias is gap junction channel protein connexin-43 (Cx43), which ensure cell-to-cell coupling for electrical signal propagation. Therefore, we aimed to explore Cx43 protein abundance and its topology in hypertrophic and hypotrophic cardiac phenotype. Analysis were performed in left ventricular tissue of adult male spontaneously hypertensive rat (SHR), Wistar Kyoto rats treated for 8-weeks with L-thyroxine, methimazol or strepotozotocin to induce hyperthyroid, hypothyroid and type-1 diabetic status as well as non-treated animals. Results showed that comparing to healthy rats there was a decrease of total myocardial Cx43 and its variant phosphorylated at serine368 in SHR and hyperthyroid rats. Besides, enhanced localization of Cx43 was demonstrated on lateral sides of hypertrophied cardiomyocytes. In contrast, total Cx43 protein and its serine368 variant were increased in atrophied left ventricle of hypothyroid and type-1 diabetic rats. It was associated with less pronounced alterations in Cx43 topology. In parallel, the abundance of PKCepsilon, which phosphorylates Cx43 at serine368 that stabilize Cx43 function and distribution was reduced in hypertrophied heart while enhanced in atrophied once. Findings suggest that differences in the abundance of cardiac Cx43, its variant phosphorylated at serine368 and Cx43 topology may explain, in part, distinct propensity of hypertrophied and atrophied heart to malignant arrhythmias.

Editorial for the IJMS Special Issue "Progress in Understanding of Cardiac Arrhythmia Mechanisms and Antiarrhythmic Targets"

Cardiac rhythm disorders, in particular life-threatening ventricular fibrillation and stroke-provoking fibrillation of the atria, are a permanent focus of both clinical and experimental cardiologists [...].

Does Myocardial Atrophy Represent Anti-Arrhythmic Phenotype?

This review focuses on cardiac atrophy resulting from mechanical or metabolic unloading due to various conditions, describing some mechanisms and discussing possible strategies or interventions to prevent, attenuate or reverse myocardial atrophy. An improved awareness of these conditions and an increased focus on the identification of mechanisms and therapeutic targets may facilitate the development of the effective treatment or reversion for cardiac atrophy. It appears that a decrement in the left ventricular mass itself may be the central component in cardiac deconditioning, which avoids the occurrence of life-threatening arrhythmias. The depressed myocardial contractility of atrophied myocardium along with the upregulation of electrical coupling protein, connexin43, the maintenance of its topology, and enhanced PKCƐ signalling may be involved in the anti-arrhythmic phenotype. Meanwhile, persistent myocardial atrophy accompanied by oxidative stress and inflammation, as well as extracellular matrix fibrosis, may lead to severe cardiac dysfunction, and heart failure. Data in the literature suggest that the prevention of heart failure via the attenuation or reversion of myocardial atrophy is possible, although this requires further research.

[Features of vectorcardiograms in patients with hypertension complicated by chronic heart failure with reduced left ventricle ejection fraction]

AIM

To explore the features of vectorcardiograms (VCG) of patients with essential hypertension complicated by chronic heart failure with reduced left ventricular ejection fraction (CHFrLVEF).

MATERIALS AND METHODS

We analyzed VCGs of 70 hypertensive patients with CHFrLVEF and 275 hypertensive patients without clinical signs of CHF and with LVEF50%. We assessed the presence of rhythm and conduction disturbances, and the parameters of the synthesized VCG, i.e., module of the maximum QRS vector, planarity index of the spatial QRS loop (P/S), and spatial angle between the integral QRS and T vectors (sQRS-Ta).

RESULTS

In hypertensive patients with CHF, certain conditions were detected more often as compared with hypertensive patients without CHF, i.e., atrial fibrillation (AF) in 52.9% vs 5.1%; p0.0001, and left bundle branch block (LBBB) in 38.6% vs 0.4%; p0.0001. The module of the maximum QRS vector and sQRS-Ta were significantly greater and P/S was significantly less in VCGs of patients with CHF. ROC-analysis showed that the presence of AF and LBBB just as VCG parameters assessed in this study provide clear discrimination between hypertensive patients with or without CHF both in the group as a whole and in the subgroups (1) without LBBB, (2) with sinus rhythm, and (3) with AF. sQRS-Ta was the most informative parameter (threshold 137, sensitivity 91%, specificity 92%). The P/S indicator at the optimal threshold value 0.92 was characterized by lower specificity (68%) with rather high sensitivity (79%).

CONCLUSION

AF, LBBB, increased module of the maximum QRS vector and sQRS-Ta, and decreased P/S index are present in hypertensive patients with CHFrLVEF as compared with patients without CHF.

Implication of Different ECG Left Ventricular Hypertrophy in Patients Undergoing Transcatheter Aortic Valve Replacement

Background

Various ECG criteria for left ventricular hypertrophy (LVH) have been proposed, but their association with clinical outcomes in patients with severe aortic stenosis undergoing transcatheter aortic valve replacement is unknown. We investigated the prevalence of ECG LVH according to different criteria and its prognostic impact on clinical outcomes after transcatheter aortic valve replacement.

Methods and Results

In this prospective observational cohort, we evaluated 700 patients who underwent transcatheter aortic valve replacement between March 2010 and December 2019. Baseline preprocedural LVH was defined by 3 ECG criteria—Sokolow‐Lyon, Romhilt‐Estes, and Cornell voltage criteria. The primary outcome was major adverse cardiac or cerebrovascular event (MACCE; composite of death, myocardial infarction, stroke, or rehospitalization from cardiovascular cause); the key secondary outcome was all‐cause and cardiovascular mortality. Among 596 eligible patients, the prevalence of LVH was determined as 56.3% by Sokolow‐Lyon, 31.1% by Romhilt‐Estes, and 48.1% by Cornell criteria. Regardless of the criteria, patients with ECG LVH had more severe aortic stenosis hemodynamics and higher left ventricular mass index. After multivariate adjustment, the presence of LVH by the Cornell criteria was significantly associated with lower risks of MACCE (adjusted hazard ratio [HR], 0.68; 95% CI, 0.51–0.91; P=0.009), all‐cause mortality (adjusted HR, 0.55; 95% CI, 0.34–0.90 [P=0.017]), and cardiovascular mortality (adjusted HR, 0.40; 95% CI, 0.20–0.79 [P=0.008]). However, this association was absent with the Sokolow‐Lyon and Romhilt‐Estes criteria.

Conclusions

ECG LVH by Cornell criteria only was significantly associated with lower risks of MACCE and all‐cause or cardiovascular mortality.

Registration

URL: https://www.clinicaltrials.gov; Unique identifier: NCT03298178.

Protein Kinase C-Mediated Hyperphosphorylation and Lateralization of Connexin 43 Are Involved in Autoimmune Myocarditis-Induced Prolongation of QRS Complex

Myocarditis is a serious and potentially life-threatening disease, which leads to cardiac dysfunction and sudden cardiac death. An increasing number of evidence suggests that myocarditis is also a malignant complication of coronavirus pneumonia, associated with heart failure and sudden cardiac death. Prolonged QRS complexes that are related to malignant arrhythmias caused by myocarditis significantly increase the risk of sudden cardiac death in patients. However, the molecular mechanisms are not fully known at present. In this study, we identify protein kinase C (PKC) as a new regulator of the QRS complex. In isolated hearts of normal rats, the PKC agonist, phorbol-12-myristate-13-acetate (PMA), induced prolongation of the QRS complex. Mechanistically, hyperphosphorylation and lateralization of connexin 43 (Cx43) by PKC induced depolymerization and internalization of Cx43 gap junction channels and prolongation of the QRS duration. Conversely, administration of the PKC inhibitor, Ro-32-0432, in experimental autoimmune myocarditis (EAM) rats after the most severe inflammation period still significantly rescued the stability of the Cx43 gap junction and alleviated prolongation of the QRS complex. Ro-32-0432 reduced phosphorylation and blocked translocation of Cx43 in EAM rat heart but did not regulate the mRNA expression level of ventricular ion channels and the other regulatory proteins, which indicates that the inhibition of PKC might have no protective effect on ion channels that generate ventricular action potential in EAM rats. These results suggest that the pharmacological inhibition of PKC ameliorates the prolongation of the QRS complex via suppression of Cx43 hyperphosphorylation, lateralization, and depolymerization of Cx43 gap junction channels in EAM rats, which provides a potential therapeutic strategy for myocarditis-induced arrhythmias.

MiR-27a-3p/Hoxa10 Axis Regulates Angiotensin II-Induced Cardiomyocyte Hypertrophy by Targeting Kv4.3 Expression

Cardiac hypertrophy is a common pathological process of various cardiovascular diseases, which is often accompanied with structural and electrical remodeling, and can even lead to sudden cardiac death. However, its molecular mechanism still remains largely unknown. Here, we induced cardiomyocyte hypertrophy by angiotensin II (Ang II), and found that miR-27a-3p and hypertrophy-related genes were up-regulated. Further studies showed that miR-27a-3p-inhibitor can alleviate myocardial hypertrophy and electrical remodeling. Moreover, luciferase assay confirmed that miR-27a-3p could regulate the expression of downstream Hoxa10 at the transcriptional level by targeting at its 3′UTR. At the same time, the protein expression of Hoxa10 was significantly reduced in Ang II-treated cardiomyocytes. Furthermore, overexpression of Hoxa10 can reverse myocardial hypertrophy and electrical remodeling induced by Ang II in cardiomyocytes. Finally, we found that Hoxa10 positively regulated the expression of potassium channel protein Kv4.3 which was down-regulated in hypertrophic cardiomyocytes. Taken together, our results revealed miR-27a-3p/Hoxa10/Kv4.3 axis as a new mechanism of Ang II-induced cardiomyocyte hypertrophy, which provided a new target for clinical prevention and treatment of cardiac hypertrophy and heart failure.

Certain beta blockers (e.g., bisoprolol) may be reevaluated in hypertension guidelines for patients with left ventricular hypertrophy to diminish the ventricular arrhythmic risk

Hypertensive left ventricular hypertrophy (HTN LVH) is associated with almost threefold increased risk of ventricular tachycardia (VT)/ventricular fibrillation (VF). Furthermore, HTN LVH increases the risk of sudden cardiac death (SCD). The reverse LV remodeling due to efficient antihypertensive therapy lowers the incidence rates of cardiovascular events and SCD and the vast majority of available arterial hypertension (HTN) guidelines recommend renin angiotensin system (RAS) blockers and calcium channel blockers (CCBs) for HTN LVH aiming for LVH regression. On the other hand, beta blockers (BBs) as a class are not recommended in HTN LVH due to their insufficient capacity to reverse LVH remodeling even though they are recommended as the first-line drugs for prevention/treatment of VT/VF (in general, unrelated to HTN LVH). Moreover, BBs are the best antiarrhythmic (against VT/VF) among antihypertensive drugs. Despite that, BBs are currently not recommended for LVH treatment in HTN Guidelines. It is important to prevent VT/VF in patients at high risk, such as those with HTN LVH. Therefore, certain BBs (such as Bisoprolol) may be reevaluated in guidelines for HTN (in the section of HTN LVH).

The electrocardiogram: Still a useful marker for LV fibrosis in aortic stenosis

Left ventricular (LV) strain on the electrocardiogram (ECG) (down-sloping, convex ST-segment depression with asymmetric T-wave inversion in leads V5 and V6) reflects fibrosis as a result of subendocardial ischemia. It is associated with a significantly increased risk of cardiovascular events independent of the presence of LV hypertrophy on the echocardiogram or cardiac magnetic resonance (CMR) scan. Ongoing studies of early aortic valve replacement in asymptomatic patients with severe aortic stenosis are using ECG changes as a marker of possible fibrosis shown by midwall late gadolinium enhancement on CMR. However, until these studies report, it is still reasonable to respond to LV strain on the ECG by tightening control of systemic hypertension and consider intervention in cases where indications are otherwise in borderline.

Electrocardiographic markers of increased risk of sudden cardiac death in patients with COVID-19 pneumonia

Background

Little is known about the role of ECG markers of increased risk of sudden cardiac death during the acute period of coronavirus disease 2019 ( COVID‐19) pneumonia.

Objectives

To evaluate ECG markers of sudden cardiac death on admission, including the index of cardiac electrophysiological balance (iCEB) (QTc/QRS) and transmural dispersion of repolarization (TDR) (T from peak to end (Tp‐e) interval and Tp‐e/QTc), in patients with COVID‐19 pneumonia.

Patients and methods

This cross‐sectional study included 63 patients with newly diagnosed COVID‐19 pneumonia who presented to the outpatient clinic or admitted to the respiratory care unit between August 20 and September 15, 2020. Forty‐six persons matched for sex and age were selected from data collected before COVID‐19 pandemic.

Results

QRS and QTc showed a significant prolongation in patients with COVID‐19 pneumonia compared to the controls (87 vs. 78, p < .00, and 429 versus. 400, p < .00, respectively). After categorization of patients with COVID‐19 pneumonia into 3 groups according to the severity of pneumonia as mild‐moderate, severe, and critical groups, a decreased values of QRS were observed in the critical COVID‐19 pneumonia group compared to severe and mild‐moderate COVID‐19 pneumonia groups (p = .04) while increased values of QTc and iCEB(QTc/QRS) were noted in critical COVID‐19 pneumonia group compared to other 2 groups(p < .00).

Conclusions

Patients with COVID‐19 pneumonia showed significant changes in repolarization and conduction parameters compared to controls. Patients with mild to severe COVID‐19 pneumonia may be at low risk for torsades de pointes development.

R-Wave Singularity: A New Morphological Approach to the Analysis of Cardiac Electrical Dyssynchrony

R-wave singularity (RWS) measures the intermittence or discontinuousness of R waves. It has been broadly used in QRS (QRS complex of electrocardiogram) detection, electrocardiogram (ECG) beats classification, etc. In this article, we novelly developed RWS to the analysis of QRS morphology as the measurement of ventricular dyssynchrony and tested the hypothesis that RWS could enhance the discrimination between control and acute myocardial infarction (AMI) patients. Holter ECG recordings were obtained from the Telemetric and Holter ECG Warehouse database, among which database Normal was extracted as normal controls (n = 202) and database AMI (n = 93) as typical subjects of autonomic nervous system dysfunction and cardiac electrical dyssynchrony with high risk for cardiac arrhythmias and sudden cardiac death. Experimental results demonstrate that RWS measured by Lipschitz exponent calculated from 5-min Holter recordings was significantly less negative in early AMI and late AMI than that in Normal subjects for overall, elderly, and elderly male groups, which suggested the heterogeneous depolarization of the ventricular myocardium during AMI. Receiver operating characteristic curve analyses show that combined with heart rate variability parameters, Lipschitz exponent provides higher accuracy in distinguishing between the patients with AMI and healthy control subjects for overall, elderly, elderly male, and elderly female groups. In summary, our study demonstrates the significance of using RWS to probe the cardiac electrical dyssynchrony for AMI. Lipschitz exponent may be valuable and complementary for existing cardiac resynchronization therapy and autonomic nervous system assessment.

Apparent electrocardiogram left ventricular hypertrophy during tachycardia

The electrocardiographic transient display of left ventricular hypertrophy (LVH), during rapid heart rates, in the setting of sinus/supraventricular tachycardias and atrial fibrillation, is illustrated via 3 case reports. This common occurrence is expressed by an increase in the S-waves in leads V2-V5, during tachycardias, rendering a false positive diagnosis of LVH by the frequently employed Cornell voltage LVH criteria. This tachycardia-mediated apparent LVH, is unrelated to the occasionally encountered stable, and unrelated to tachycardia, "false positive diagnosis of LVH", which could in reality occasionally reflect altered electrical properties of myocardium that could create a functional substrate for developing arrhythmias. The importance of awareness of this insight by all health professionals is immeasurable, considering that a false positive diagnosis of LVH has major consequences in the management, prognostication, resort to expensive unnecessary testing, and stress to the patients and their families.

Pro-Arrhythmic Signaling of Thyroid Hormones and Its Relevance in Subclinical Hyperthyroidism

A perennial task is to prevent the occurrence and/or recurrence of most frequent or life-threatening cardiac arrhythmias such as atrial fibrillation (AF) and ventricular fibrillation (VF). VF may be lethal in cases without an implantable cardioverter defibrillator or with failure of this device. Incidences of AF, even the asymptomatic ones, jeopardize the patient's life due to its complication, notably the high risk of embolic stroke. Therefore, there has been a growing interest in subclinical AF screening and searching for novel electrophysiological and molecular markers. Considering the worldwide increase in cases of thyroid dysfunction and diseases, including thyroid carcinoma, we aimed to explore the implication of thyroid hormones in pro-arrhythmic signaling in the pathophysiological setting. The present review provides updated information about the impact of altered thyroid status on both the occurrence and recurrence of cardiac arrhythmias, predominantly AF. Moreover, it emphasizes the importance of both thyroid status monitoring and AF screening in the general population, as well as in patients with thyroid dysfunction and malignancies. Real-world data on early AF identification in relation to thyroid function are scarce. Even though symptomatic AF is rare in patients with thyroid malignancies, who are under thyroid suppressive therapy, clinicians should be aware of potential interaction with asymptomatic AF. It may prevent adverse consequences and improve the quality of life. This issue may be challenging for an updated registry of AF in clinical practice. Thyroid hormones should be considered a biomarker for cardiac arrhythmias screening and their tailored management because of their multifaceted cellular actions.