This is most commonly the result of longstanding high blood pressure, or hypertension, which has caused a maladaptive change to the wall of the main pumping chamber of the heart, the left ventricle. Increased blood pressure means that the heart must pump even harder to adequately circulate blood throughout the body. If the heart does this for a prolonged period of time due to uncontrolled hypertension, the left ventricle can hypertrophy (grow larger) in a way that decreases the effectiveness of the heart. Left ventricular hypertrophy can be demonstrated on echocardiogram and electrocardiogram (EKG).A 1999 review of sudden cardiac deaths in the United States found that structural heart diseases accounted for over 30% of sudden cardiac arrests for those under 30 years. A study of military recruits age 18-35 found that this accounted for over 40% of sudden cardiac deaths.Congestive heart failure increases the risk of sudden cardiac death fivefold.Structural abnormalities of the cardiac conduction system (notably the Atrioventricular Node and His-Purkinje system) may predispose an individual to arrhythmias with risk of progressing to sudden cardiac arrest, albeit this risk remains low. Many of these conduction blocks can be treated with internal cardiac defibrillators for those determined to be at high risk due to severity of fibrosis or severe electrophysiologic disturbances. : 833

Inherited arrhythmia syndromes
Arrhythmias that are not due to structural heart disease account for 5 to 10% of sudden cardiac arrests. These are frequently caused by genetic disorders that lead to abnormal heart rhythms.
Double outlet right ventricle (DORV) is a form of congenital heart disease where both of the great arteries connect (in whole or in part) to the right ventricle (RV). In some cases it is found that this occurs on the left side of the heart rather than the right side. Cause
Pathogenesis
DORV occurs in multiple forms, with variability of great artery position and size, as well as of ventricular septal defect (VSD) location. It can occur with or without transposition of the great arteries. The clinical manifestations are similarly variable, depending on how the anatomical defects affect the physiology of the heart, in terms of altering the normal flow of blood from the RV and left ventricle (LV) to the aorta and pulmonary artery. For example:
in DORV with a subaortic VSD, blood from the LV flows through the VSD to the aorta and blood from the RV flows mainly to the pulmonary artery, yielding physiology similar to ventricular septal defect
in DORV with a subpulmonic VSD (called Taussig-Bing syndrome), blood from the LV flows through the VSD to the pulmonary artery and blood from the RV flows mainly to the aorta, yielding physiology similar to Transposition of the Great Arteries
but if there is pulmonic stenosis in addition, physiology resembles Tetralogy of Fallot
in other forms of DORV, blood from both ventricles is substantially mixed in the RV, yielding physiology that resembles a large VSD
but again, if there is pulmonic stenosis, physiology resembles Tetralogy of Fallot

Treatment
DORV is treated with surgery.