Figure 8. A, Intracardiac electrograms during activation mapping. There are 2 paced beats from the Lasso in the right inferior pulmonary vein (RIPV) followed by a sinus beat. The ablator is on the posterior left atrium (LA). During RIPV pacing, earliest activation is in the Crista followed by simultaneous LA and proximal coronary sinus (CS) activation. The sinus beat shows early activation in the RIPV, then CS and LA. B, Activation map of LA and right atrium (RA) during pacing from the RIPV. During RIPV pacing, earliest activation is in the RSPV, then posterior RA, then CS, and posterior LA. by guest on May 12, 2018

Sudden cardiac death (SCD) is a very prevalent cause of death in the United States. The majority of individuals who experience SCD do not survive the episode. Although there are ongoing efforts to improve resuscitation (ie, training in cardiopulmonary resuscitation, easy access to automatic external defibrillators), the primary modality addressing this public health problem is prevention by identification and treatment of high-risk cohorts. Current screening techniques have focused on identifying patients for primary prevention of ventricular tachyarrhythmias. Primary prevention therapies include medications, such as beta-blockers, statins, and angiotensin-converting enzyme inhibitors, and the implantable cardioverter defibrillator (ICD), whose use is currently focused on only the highest-risk subpopulations. The high-risk groups that are currently screened for consideration of an ICD for either primary or secondary prevention of SCD include those with a variety of cardiomyopathies, those with a history of previous aborted SCD, and those with genetic predispositions. In patients with ischemic cardiomyopathy and nonischemic dilated cardiomyopathy, the primary screening parameter to identify the highest-risk group (which is then subsequently screened for consideration of an ICD) is left ventricular ejection fraction (LVEF). Various other clinical factors and noninvasive test results are often combined with this information, but the optimal way in which this should be done has not been established. The array of noninvasive tests available includes those focusing on depolarization abnormalities, repolarization abnormalities, disturbed autonomic responses, and imaging. Unfortunately, current risk-stratification paradigms do not identify the majority of patients who will experience SCD. The fundamental reason for this is that the risk of SCD is truly lower in those without high-risk features such as depressed LVEF; however, the much larger number of patients with these lower-risk features translates into a larger absolute number of SCDs in this lower-risk group. In order to widen the scope of risk stratification, careful clinical study will be needed to develop appropriate testing strategies that can reliably identify patients at significant risk for ventricular tachyarrhythmias in the broader population.

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