J point is the end of the QRS complex, marking the end of ventricular depolarization and the junction between depolarization and repolarization. J wave is a deflection with a dome or hump in the same direction as the R wave . Classically a wave at the J point occurring in hypothermia has been called Osborn wave after the seminal work of John J Osborn .
Important J wave syndromes are Early Repolarization Syndrome and Brugada syndrome . Early repolarization syndrome was initially considered as a benign condition till Haïssaguerre M et al highlighted the relation between sudden cardiac arrest and early repolarization . They defined early repolarization as an elevation of QRS-ST junction of at least 0.1 mV from baseline in inferior or lateral leads, manifested as QRS slurring or notching. They compared 206 subjects resuscitated after sudden cardiac arrest due to idiopathic ventricular fibrillation and 412 subjects without heart disease, who were matched for age, gender, race and level of physical activity. Early repolarization was noted in 31% of those with idiopathic ventricular fibrillation while it was seen in only 5% of the controls (P<0.001). During a mean follow up period of 61 months, monitoring with implantable defibrillator showed higher incidence of recurrent ventricular fibrillation in those with a repolarization abnormality.
Antzelevitch C et al divided early repolarization syndrome into three types. Type 1 was early repolarization pattern predominantly in lateral leads, prevalent in healthy male athletes. Type 2 was predominantly in inferior and inferolateral leads and associated with a higher level of risk. Type 3 displayed early repolarization pattern globally in inferior, lateral and right precordial leads and was associated with highest level of risk for development of malignant arrhythmias and ventricular fibrillation storms .
J wave is mediated by the transient outward potassium current Ito. It has been suggested that arrhythmias associated early repolarization, Brugada syndrome, hypothermia and those occurring in the acute phase of ST elevation myocardial infarction are linked to abnormalities in Ito mediated J wave .
Haïssaguerre M, Derval N, Sacher F, Jesel L, Deisenhofer I, de Roy L, Pasquié JL, Nogami A, Babuty D, Yli-Mayry S, De Chillou C, Scanu P, Mabo P, Matsuo S, Probst V, Le Scouarnec S, Defaye P, Schlaepfer J, Rostock T, Lacroix D, Lamaison D, Lavergne T, Aizawa Y, Englund A, Anselme F, O’Neill M, Hocini M, Lim KT, Knecht S, Veenhuyzen GD, Bordachar P, Chauvin M, Jais P, Coureau G, Chene G, Klein GJ, Clémenty J. Sudden cardiac arrest associated with early repolarization. N Engl J Med. 2008 May 8;358(19):2016-23.