Unique Rhythm Phenomena and Mechanisms

It is of critical importance in clinical cardiology practice to recognize unique rhythm phenomena and understand the underlying mechanisms as well as the associated clinical implications. Our primary objective in this chapter thus is to discuss several specific rhythm phenomena, which are unique, but also commonly seen in clinical practice. We have chosen to highlight the Ashman phenomenon, cardiac (T wave) memory, concealed conduction, gap phenomenon, phase 3 block, phase 4 block and Inverse Wenckebach (not traditionally defined Reverse Wenckebach), supernormal conduction, and Wedensky phenomenon. Recent progress in both basic and clinical research has provided new insights into these unique rhythm phenomena. Three examples of such revelations include 1) novel evidence of Wenckebach conduction (at a cellular level) in ventricular myocardium; 2) Inverse Wenckebach, a newly observed ECG phenomenon that is associated with paroxysmal AV block; and 3) cardiac (T wave) memory, a misleading ECG phenomenon and concept that has caused tremendous confusion in clinical practice.