J wave

A J wave — also known as Osborn wave, camel-hump sign, late delta wave, hathook junction, hypothermic wave,^[1] K wave, H wave or current of injury — is an abnormal electrocardiogram finding.^[2]

J waves are positive deflections occurring at the junction between the QRS complex and the ST segment,^[3][4] where the S point, also known as the J point, has a myocardial infarction-like elevation.

They are usually observed in people suffering from hypothermia with a temperature of less than 32 °C (90 °F),^[5] though they may also occur in people with very high blood levels of calcium (hypercalcemia), brain injury, vasospastic angina, acute pericarditis, or they could also be a normal variant.^{[citation needed]} Osborn waves on ECG are frequent during targeted temperature management (TTM) after cardiac arrest, particularly in patients treated with 33 °C.^[6] Osborn waves are not associated with increased risk of ventricular arrhythmia, and may be considered a benign physiological phenomenon, associated with lower mortality in univariable analyses.^[6]

The J wave reflects the transmural gradient of amplitude of the cardiac transient outward K+ current: channels responsible for this current exhibit differential expression across ventricular myocardium, producing a more potent current in the epicardium than the endocardium.^[7]

The prominent J deflection attributed to hypothermia was first reported in 1938 by Tomaszewski. These waves were then definitively described in 1953 by John J. Osborn (1917–2014) and were named in his honor.^[8] Over time, the wave has increasingly been referred to as a J wave, though is still sometimes referred to as the Osborn wave in most part due to Osborn's article in the American Journal of Physiology on experimental hypothermia.^[9]