N.A. Mark Estes

2012 ACCF/AHA/HRS Focused Update of the 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities

Developed in Collaboration With the American Association for Thoracic Surgery, Heart Failure Society of America, and Society of Thoracic Surgeons

Long QT Syndrome, Brugada Syndrome, Right Ventricular Cardiomyopathy, Hypertrophic Cardiomyopathy, and Commotio Cordis

The hereditary long QT syndrome (LQTS) is a rare disorder characterized by prolongation of the QT interval on the electrocardiogram (ECG) and a propensity for syncope, torsades de pointes, ventricular arrhythmias, and sudden death. One form of LQTS, described by Jervell and Lange-Neilsen in 1957, is characterized by deafness and autosomal recessive inheritance (1). The most common form of LQTS was initially described by Romano (2) and Ward (3), and is characterized by autosomal dominant inheritance and normal hearing. Remarkable progress has been made in the last several years in our understanding of the pathogenesis of LQTS. It is now clear that LQTS is a heterogeneous disorder caused by mutations in specific ion channels that play a critical role in the control of cardiac repolarization (4). These findings have revolutionized our understanding of LQTS, and may yield new insights into other conditions characterized by ventricular arrhythmias in the absence of ischemia or structural heart disease. Recent work has also identified LQTS as an important cause of sudden infant death syndrome (SIDS) (5,6).

The Advantages and Disadvantages of Creating Large Radiofrequency Ablation Lesions

Radiofrequency ablation has become a major therapeutic modality in the treatment of cardiac arrhythmias. Most forms of supraventricular tachycardia have been successfully treated with catheter-based techniques using focal ablative radiofrequency lesions. A large range of other arrhythmias, however, may be treated using longer, wider, and deeper lesions. A long linear lesion may be particularly important in the ablation of reentrant arrhythmias that have a critical zone 1-cm or more in length. Such a critical zone may exist between two or more anatomic structures, such as in atrial flutter, scar-related reentrant tachycardias, some atrial tachycardias, and some ventricular tachycardias (Figure 1). A series of linear lesions may also be effective in preventing perpetuation of reentrant wavefronts in such disorders as atrial fibrillation (Figure 2). A line of lesions may be placed circumferentially when it is not possible or desirable to ablate the arrhythmia focus itself (Figure 3). This approach may be useful in some ventricular tachycardias and in focal atrial fibrillation ablation in pulmonary veins. There are situations in which the reentrant circuit may be complex and it is not possible to ablate all the critical zones. It may be possible to transect the zone in such cases as ischemic-based ventricular tachycardia (Figure 4). Wide lesions may be necessary when the reentrant circuit spans a large surface area subendocardial (Figure 5).