The J point
The J point is the the junction between the termination of the QRS complex and the beginning of the ST segment.
The J (junction) point marks the end of the QRS complex, and is often situated above the baseline, particularly in healthy young males.
On most ECGs the determination of the J point as a demarcation between QRS and the start of the ST is clear. However with the advance of electrophysiological studies and scrutiny of the cellular/ionic mechanisms at each stage of the ECG – these lines become blurred.
- J point is present in all ECGs and marks the transition of QRS complex to ST segment
- J wave deflection occurs before the J point
- The position of the J point in relation to a slurred terminal QRS is still debated.
Note: The letter J on the ECG defines 2 totally different and unrelated events. The J point is a point in time marking the end of the QRS and the onset of the ST segment present on all ECG’s; the J wave is a much less common long slow deflection of uncertain origin originally described in relation to hypothermia.
Abnormalities of the J point
- Elevation or depression of the J point is seen with the various causes of ST segment abnormality. It may be elevated as a result of injury currents during acute myocardial ischemia and pericarditis, as well as in various other patterns of both normal and abnormal ECGs
- Elevation of the J point occurs with benign early repolarisation
- A positive deflection prior to the J point is termed a J wave (Osborn wave) and is characteristically seen with hypothermia.
- Gussak I, Antzelevitch C. Early repolarization syndrome: clinical characteristics and possible cellular and ionic mechanisms. J Electrocardiol. 2000;33:299-309. [PMID 11099355]
- Tikkanen JT, Anttonen O, Junttila MJ, et al. Long-term outcome associated with early repolarization on electrocardiography. N Engl J Med. 2009;361:2529-2537. [PMID 19917913]
- Surawicz B, Macfarlane PW. Inappropriate and confusing electrocardiographic terms: J-wave syndromes and early repolarization. J Am Coll Cardiol. 2011;57:1584-1586. [PMID 21474037]
- Perez MV, Friday K, Froelicher V. Semantic confusion: the case of early repolarization and the J point. Am J Med. 2012 Sep;125(9):843-4. [PMID 22340816]
- Haissaguerre M, Derval N, Sacher F. et al. Sudden cardiac arrest associated with early repolarization. N Engl J Med. 2008;358: 2016–2023. [PMID 18463377]
ECG Library Basics
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Rawshani A. Clinical ECG Interpretation
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health, a Clinical Adjunct Associate Professor at Monash University, and the Chair of the Australian and New Zealand Intensive Care Society (ANZICS) Education Committee. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of LITFL.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of two amazing children.
On Twitter, he is @precordialthump.