From GeneReviews Overview
Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the EKG that are associated with tachyarrhythmias, typically the ventricular tachycardia torsade de pointes (TdP). TdP is usually self-terminating, thus causing a syncopal event, the most common symptom in individuals with LQTS. Such cardiac events typically occur during exercise and emotional stress, less frequently during sleep, and usually without warning. In some instances, TdP degenerates to ventricular fibrillation and causes aborted cardiac arrest (if the individual is defibrillated) or sudden death. Approximately 50% of untreated individuals with a pathogenic variant in one of the genes associated with LQTS have symptoms, usually one to a few syncopal events. While cardiac events may occur from infancy through middle age, they are most common from the preteen years through the 20s. Some types of LQTS are associated with a phenotype extending beyond cardiac arrhythmia. In addition to the prolonged QT interval, associations include muscle weakness and facial dysmorphism in Andersen-Tawil syndrome (LQTS type 7); hand/foot, facial, and neurodevelopmental features in Timothy syndrome (LQTS type 8); and profound sensorineural hearing loss in Jervell and Lange-Nielson syndrome.

From OMIM
Loss-of-function mutations in ANK2 can result in a broad spectrum of clinical cardiac phenotypes. Carriers of some mutations (e.g., E1425G, 106410.0001) display QT interval prolongation, stress- and/or exercise-induced polymorphic ventricular arrhythmia, syncope, and sudden cardiac death. Patients with other variants show clinical phenotypes, sometimes mild, extending beyond LQTS, leading to the label 'ankyrin-B syndrome.' These phenotypes include bradycardia, sinus arrhythmia, delayed conduction/conduction block, idiopathic ventricular fibrillation, and catecholaminergic polymorphic ventricular tachycardia (Mohler et al., 2007).  http://www.omim.org/entry/600919

From MedlinePlus Genetics
Ankyrin-B syndrome is associated with a variety of heart problems related to disruption of the heart's normal rhythm (arrhythmia). Heart rhythm is controlled by electrical signals that move through the heart in a highly coordinated way. In ankyrin-B syndrome, disruption of different steps of electrical signaling can lead to arrhythmia, and the resulting heart problems vary among affected individuals.

Individuals with ankyrin-B syndrome may have problems with the sinoatrial (SA) node, which generates the electrical impulses that start each heartbeat. If the SA node is not functioning properly, the heartbeat can be too slow (bradycardia). In a small number of people with ankyrin-B syndrome, the heart takes longer than usual to recharge between beats, which is known as a prolonged QT interval (long QT). Some affected individuals have impaired progression (conduction) of electrical impulses between the chambers of the heart, which can cause a problem called heart block. Other heart problems that occur in ankyrin-B syndrome include irregular and uncoordinated electrical activity in the heart's upper chambers (atrial fibrillation) or lower chambers (ventricular fibrillation) and an abnormality called catecholaminergic polymorphic ventricular tachycardia (CPVT), in which an increase in the heart rate can trigger an abnormally fast and irregular heartbeat called ventricular tachycardia. In people with ankyrin-B syndrome, arrhythmia can lead to fainting (syncope) or cardiac arrest and sudden death.

When associated with a prolonged QT interval, the condition is sometimes classified as long QT syndrome 4. However, because additional heart problems can result from changes in the same gene, long QT syndrome 4 is usually considered part of ankyrin-B syndrome.  https://medlineplus.gov/genetics/condition/ankyrin-b-syndrome