Arrhythmogenic Effects of Cardiac Memory

Abstract

Cardiac memory is the term used to describe an interesting electrocardiographic phenomenon. Whenever a QRS complex is wide and abnormal, such as during ventricular pacing, the T waves will also be abnormal and will point to the opposite direction of the wide QRS. If the QRS then normalizes, such as after cessation of ventricular pacing, the T waves will normalize as well, but at a later stage. The period of cardiac memory is the phase between the sudden normalization of the QRS and the eventual and gradual return of the T waves to their baseline morphology. Cardiac memory is assumed to be an innocent electrocardiographic curiosity. However, during cardiac memory, reduction of repolarizing potassium currents increases left ventricular repolarization gradients. Therefore, when cardiac memory occurs in patients who already have a prolonged QT interval (for whatever reason), it can lead to a frank long QT syndrome with QT-related ventricular arrhythmias (torsades de pointes). These arrhythmogenic effects of cardiac memory are not generally appreciated and are reviewed here for the first time.

Unraveling Complexities in Genetically Elusive Long QT Syndrome

“…Environmental factors can play a significant role in the development of QT prolongation, and a subset of genotype-negative patients with LQTS may in fact have an acquired, often underrecognized cause of QT prolongation. The ever-growing list of external triggers that are known to have arrhythmogenic QT-prolonging capabilities includes over 200 medications (most with noncardiac indications; as summarized in www.crediblemeds.org), electrolyte imbalances (particularly hypokalemia, hypomagnesemia, and hypocalcemia), hypothyroidism, but also myocardial healing from stress cardiomyopathy, 19,20 arrhythmogenic cardiac memory, 21 and certain foods/nutritional status (eg, anorexia nervosa, low-calorie-diet, alcohol intoxication, and grapefruit juice). 22,23 There is also robust data supporting the role of anti-Ro/SSA antibodies, often detected in patients with connective tissue diseases and Sjogren syndrome, in acquired LQTS and predisposition to TdP.…”

Contributions of Israel to the field of clinical cardiac electrophysiology and implantable devices

“…These arrhythmogenic effects of cardiac memory have been reviewed here for the first time by Viskin and coworkers. 220 …”

Long QT begets long QT

“…Although the congenital and the drug‐induced long QT syndromes (LQTS) were first recognized >50 years ago, 1 new forms of LQTS continue to be described 2 . The latest forms include the LQTS caused by myocardial healing, 3,4 strenuous sports, 5 proarrhythmic food 6 or arrhythmogenic cardiac memory 7 . Even today, telling apart LQTS‐patients who will develop QT‐related arrhythmias (torsade‐de‐pointes), from those who will remain asymptomatic, remains challenging.…”

“…2 The latest forms include the LQTS caused by myocardial healing, 3,4 strenuous sports, 5 proarrhythmic food 6 or arrhythmogenic cardiac memory. 7 Even today, telling apart LQTS-patients who will develop QT-related arrhythmias (torsadede-pointes), from those who will remain asymptomatic, remains challenging. In this issue of the Journal, Marril et al demonstrate that some of the electrocardiographic (ECG) parameters accepted as high-risk markers for imminent torsade-de-pointes, are not as reliable as expected.…”