The Mechanism of Ajmaline and Thus Brugada Syndrome: Not Only the Sodium Channel!

Primary Electrical Heart Disease-Principles of Pathophysiology and Genetics

Primary electrical heart diseases, often considered channelopathies, are inherited genetic abnormalities of cardiomyocyte electrical behavior carrying the risk of malignant arrhythmias leading to sudden cardiac death (SCD). Approximately 54% of sudden, unexpected deaths in individuals under the age of 35 do not exhibit signs of structural heart disease during autopsy, suggesting the potential significance of channelopathies in this group of age. Channelopathies constitute a highly heterogenous group comprising various diseases such as long QT syndrome (LQTS), short QT syndrome (SQTS), idiopathic ventricular fibrillation (IVF), Brugada syndrome (BrS), catecholaminergic polymorphic ventricular tachycardia (CPVT), and early repolarization syndromes (ERS). Although new advances in the diagnostic process of channelopathies have been made, the link between a disease and sudden cardiac death remains not fully explained. Evolving data in electrophysiology and genetic testing suggest previously described diseases as complex with multiple underlying genes and a high variety of factors associated with SCD in channelopathies. This review summarizes available, well-established information about channelopathy pathogenesis, genetic basics, and molecular aspects relative to principles of the pathophysiology of arrhythmia. In addition, general information about diagnostic approaches and management is presented. Analyzing principles of channelopathies and their underlying causes improves the understanding of genetic and molecular basics that may assist general research and improve SCD prevention.

Sudden cardiac death in a young male endurance athlete

Sudden cardiac death (SCD) is a rare yet devastating event that can occur in young athletes. Although hypertrophic obstructive cardiomyopathy is the most common cause of SCD, some other genetic abnormalities have been identified as proarrhythmic. However, there is not routine screening for these other genetic abnormalities. Furthermore, consumption of caffeine, stimulant medication, or prolonged exercise can potentiate the underlying arrhythmic potential. In the event of SCD, advanced cardiac life support (ACLS) should be performed immediately and exactly. The authors present a case of an otherwise healthy young male who collapsed during a marathon and could not be resuscitated despite aggressive measures. After aggressive resuscitative efforts, the patient ultimately expired. A postmortem autopsy revealed no cardiac structural abnormalities, and the cause of death was determined to be cardiac arrhythmia of undetermined etiology. Postmortem genetic testing revealed a heterozygous variation in calcium voltage-gated channel auxiliary subunit beta 2 (CACNB2), a gene associated with arrhythmia and calcium channelopathy. Toxicology showed therapeutic levels of amphetamine. This case highlights the eminent risk of cardiac death in young athletes with proarrhythmic genetic variations, especially in the setting of endurance sport.

T-Peak to T-End Interval for Prediction of Positive Response to Ajmaline Challenge Test in Suspected Brugada Syndrome Patients

BACKGROUND

Brugada syndrome (BrS) is diagnosed in patients with ST-segment elevation with coved-type morphology in the right precordial leads, occurring spontaneously or after provocative drugs. Due to electrocardiographic (ECG) inconsistency, provocative drugs, such as sodium-channel blockers, are useful for unmasking BrS. Ajmaline is superior to flecainide and procainamide to provoke BrS. Prolonged T-peak to T-end (TpTe) is associated with an increased risk of ventricular arrhythmia and sudden cardiac death in Brugada syndrome patients.

OBJECTIVE

This study aimed to investigate the predictive value of T-peak to T-end interval and corrected T-peak to T-end interval for predicting the positive response of the ajmaline challenge test in suspected Brugada syndrome patients.

METHODS

Patients who underwent the ajmaline test in our center were enrolled. Clinical characteristics and electrocardiographic parameters were analyzed, including TpTe, corrected TpTe, QT, corrected QT(QTc) interval, and S-wave duration, compared with the result of the ajmaline challenge test.

RESULTS

The study found that TpTe and corrected TpTe interval in suspected BrS patients were not significantly associated with a positive response to the ajmaline challenge test.

CONCLUSIONS

The T-peak to T-end interval and corrected T-peak to T-end interval could not predict the positive response of the ajmaline challenge test in suspected Brugada syndrome patients.

Directed Biosynthesis of New to Nature Alkaloids in a Heterologous Nicotiana benthamiana Expression Host

Plants produce a wide variety of pharmacologically active molecules classified as natural products. Derivatization of these natural products can modulate or improve the bioactivity of the parent compound. Unfortunately, chemical derivatization of natural products is often difficult or impractical. Here we use the newly discovered biosynthetic genes for two monoterpene indole alkaloids, alstonine and stemmadenine acetate, to generate analogs of these compounds. We reconstitute these biosynthetic genes in the heterologous host Nicotiana benthamiana along with an unnatural starting substrate to produce the corresponding new-to-nature alkaloid product.