Supraventricular arrhythmias in noncompaction of left ventricle: Is this a frequent complication?

Cellular-level analyses of SCN5A mutations in left ventricular noncompaction cardiomyopathy suggest electrophysiological mechanisms for ventricular tachycardia

Left ventricular noncompaction cardiomyopathy (LVNC) is a cardiovascular disease characterized by arrhythmia and heart failure. In this study, LVNC myocardial samples were collected from patients who underwent heart transplantation and were analyzed using exome sequencing. Approximately half of the LVNC patients carried SCN5A variants, which are associated with clinical symptoms of ventricular tachycardia. To investigate the electrophysiological functions of these SCN5A variants and the underlying mechanism by which they increase arrhythmia susceptibility in LVNC patients, functional evaluations were conducted in CHO-K1 cells and human embryonic stem cell-derived cardiomyocytes (hESC-CMs) using patch-clamp or microelectrode array (MEA) techniques. These findings demonstrated that these SCN5A mutants exhibited gain-of-function properties, leading to increased channel activation and enhanced fast inactivation in CHO-K1 cells. Additionally, these mutants enhanced the excitability and contractility of the cardiomyocyte population in hESC-CMs models. All SCN5A variants induced fibrillation-like arrhythmia and increased the heart rate in cardiomyocytes. However, the administration of Lidocaine, an antiarrhythmic drug that acts on sodium ion channels, was able to rescue or alleviate fibrillation-like arrhythmias and secondary beat phenomenon. Based on these findings, it is speculated that SCN5A variants may contribute to susceptibility to arrhythmia in LVNC patients. Furthermore, the construction of cardiomyocyte models with SCN5A variants and their application in drug screening may facilitate the development of precise therapies for arrhythmia in the future.

PLEKHM2 mutation leads to abnormal localization of lysosomes, impaired autophagy flux and associates with recessive dilated cardiomyopathy and left ventricular noncompaction

Gene mutations, mostly segregating with a dominant mode of inheritance, are important causes of dilated cardiomyopathy (DCM), a disease characterized by enlarged ventricular dimensions, impaired cardiac function, heart failure and high risk of death. Another myocardial abnormality often linked to gene mutations is left ventricular noncompaction (LVNC) characterized by a typical diffuse spongy appearance of the left ventricle. Here, we describe a large Bedouin family presenting with a severe recessive DCM and LVNC. Homozygosity mapping and exome sequencing identified a single gene variant that segregated as expected and was neither reported in databases nor in Bedouin population controls. The PLEKHM2 cDNA2156_2157delAG variant causes the frameshift p.Lys645AlafsTer12 and/or the skipping of exon 11 that results in deletion of 30 highly conserved amino acids. PLEKHM2 is known to interact with several Rabs and with kinesin-1, affecting endosomal trafficking. Accordingly, patients' primary fibroblasts exhibited abnormal subcellular distribution of endosomes marked by Rab5, Rab7 and Rab9, as well as the Golgi apparatus. In addition, lysosomes appeared to be concentrated in the perinuclear region, and autophagy flux was impaired. Transfection of wild-type PLEKHM2 cDNA into patient's fibroblasts corrected the subcellular distribution of the lysosomes, supporting the causal effect of PLEKHM2 mutation. PLEKHM2 joins LAMP-2 and BAG3 as a disease gene altering autophagy resulting in an isolated cardiac phenotype. The association of PLEKHM2 mutation with DCM and LVNC supports the importance of autophagy for normal cardiac function.

Electrocardiographic findings in correlation to magnetic resonance imaging patterns in African patients with isolated ventricular noncompaction

OBJECTIVE

Isolated ventricular noncompaction is a rare primary genetic cardiomyopathy characterized by persistent embryonic myocardial morphology without any other cardiac anomalies. Arrhythmias are frequently present, including both tachyarrhythmia and conduction disturbance. Our study aimed to describe the electrocardiographic findings and to correlate them with the clinical presentation and cardiac magnetic resonance imaging findings.

METHODS

We retrospectively reviewed 24 patients diagnosed with isolated ventricular noncompaction (IVNC) by cardiac magnetic resonance imaging. Correlations were investigated between arrhythmias and the site of ventricular noncompaction, number of noncompacted segments, presence of fibrosis, and left ventricular dysfunction.

RESULTS

The mean age was 42.7±13.1 years. Patients were first presented with heart failure in 41.7% and arrhythmia in 45.8%. Electrocardiogram was abnormal in 91.6% of patients; the most common anomaly was left bundle branch block (LBBB) (41.7%), followed by supraventricular arrhythmias (29.1%), repolarization abnormalities (29.1%), and ventricular tachycardia (20.8%). A normal left ventricular systolic function was frequently observed in patients who first presented with rhythm disorders than heart failure (p=0.008). There was also a delayed diagnosis of IVNC when presented with arrhythmia versus heart failure (p=0.02). We found no correlation between arrhythmias and the noncompaction site or fibrosis, except for LBBB, which was associated to left ventricle lateral wall involvement (p=0.028). No correlation between systolic dysfunction and the number of noncompacted segments, fibrosis, or arrhythmia was demonstrated.

CONCLUSION

While electrocardiographic abnormalities are frequent in isolated ventricular noncompaction, no specific patterns were identified. More large studies are needed for stratification of arrhythmic risk of this highly arrhythmogenic substrate.

Focal left atrial tachycardia in a patient with left ventricular noncompaction

Left ventricular noncompaction (LVNC) is a rare disease caused by intrauterine failure of the myocardium to compact. The major clinical manifestations of LVNC include heart failure, ventricular tachyarrhythmia, thromboembolic event, and sudden deaths. Atrial arrhythmia usually seen is atrial fibrillation. We report a rare case of focal left atrial tachycardia in an 18-year-old patient who presented for evaluation of persistent tachycardia. Transthoracic echocardiogram showed severe systolic dysfunction and evidence of noncompaction of the left ventricle. A detailed review of ECG revealed the possibility of ectopic atrial tachycardia, most likely originating from the left side. Electrophysiology study showed sustained atrial tachycardia originating on the ridge anterior to the left sided pulmonary veins. A successful radiofrequency catheter ablation was performed at this site without any complications.

Left ventricular noncompaction

According to the World Health Organization classification of cardiomyopathies, left ventricular noncompaction is still an unclassified cardiomyopathy. In 2006, the American Heart Association classified this entity as a primary cardiomyopathy of genetic origin. In 2008, the European Society of Cardiology updated the classification scheme similar to the World Health Organization classification. At present, there is no consensus on the diagnostic criteria, and diagnosis is based on the morphologic features identified by cardiac imaging studies or at autopsy. Due to lack of standardization of the diagnostic criteria and little awareness of this condition among clinicians, the true prevalence of this disease is not clear. There is no specific therapy for this condition. However, it seems prognosis is much better than initially reported. The current status of diagnosis, prognosis, and management of isolated noncompaction in adults is discussed in this review.