Sudden cardiac death is one of the leading causes of death in Western countries and cardiac arrhythmias have been reported as the cause in many cases. Sudden cardiac arrest occurs when the electrical system to the heart malfunctions and suddenly becomes very irregular. The heart beats dangerously fast. The ventricles may flutter or quiver (ventricular fibrillation), and blood is not delivered to the body.
Most sudden cardiac deaths are caused by abnormal heart rhythms called arrhythmias. The most common life-threatening arrhythmia is ventricular fibrillation, which is an erratic, disorganized firing of impulses from the ventricles. Sudden cardiac death can be diagnosed in a variety of ways via an EKG, echocardiogram, MUGA test, cardiac catheterization, and blood tests.
In over half of the cases, however, sudden cardiac arrest occurs without prior symptoms. Therefore prevention and risk diagnosis are key targets in this area. Epidemiological studies have suggested that genetic factors contribute to sudden cardiac death, however, only a few genes have been identified. Now, a study from researchers at St. Marien-Hospital Mülheim has identified a gene associated with sudden cardiac death in the general population using an implantable cardioverter defibrillator (ICD). The team state that this is the first time a gene has been identified using ICD monitoring and then confirmed to be associated with sudden cardiac death in the general population.
Previous studies show that ICDs are indicated for patients who either have survived a life threatening cardiac arrhythmia or have a high risk for sudden cardiac death due to cardiac arrhythmias. ICDs continuously monitor a patient’s cardiac rhythm. They can also diagnose and treat cardiac arrhythmias, potentially preventing sudden cardiac death.
The current study included patients from the DISCOVERY trial and Oregon-SUDS (Sudden Unexpected Death Study). ICDs were first used to monitor and store cardiac arrhythmia data from 1,145 patients in the DISCOVERY trial to investigate whether specific genes were associated with an increased risk of potentially life-threatening ventricular tachyarrhythmias.
The team genotyped seven single nucleotide polymorphisms (SNPs) in three genes (GNB3, GNAQ and GNAS) coding G-protein subunits. The lab explain that G-proteins interact with stimulated adrenoreceptors, angiotensin II receptors and ion channels in myocardial cells. Earlier studies suggest that abnormal G-protein signal transduction is a mechanism contributing to sudden cardiac death, making the data findings in-line with these previous findings. The genes found to be associated with cardiac arrhythmias in the DISCOVERY trial were then validated in 1,335 patients from Oregon-SUDS.
Results show that in the DISCOVERY trial, 297 patients had a ventricular tachyarrhythmia. Genotypes of two SNPs in the GNAS gene were found to be significantly predictive of ventricular tachyarrhythmias. Data findings show one of these SNPs, GNAS, was significantly associated with sudden cardiac death in the Oregon-SUDS.
The lab state that using ICD monitoring and a sample of sudden cardiac death patients from the community they have found that a polymorphism in the GNAS gene predicts ventricular tachyarrhythmias and sudden cardiac death. Their results suggest that GNAS mediated signal transduction may have an important role in ventricular arrhythmogenesis.
The team surmise that to their knowledge this is the first time that a gene variant has been identified by monitoring ventricular tachyarrhythmias in patients with ICDs and then confirmed in a wider population. They go on to conclude that the findings may help to identify patients at increased risk of sudden cardiac death.