QTc: how long is too long?

Congenital long QT syndrome (LQTS) affects an estimated 1 in 2500 people and typically presents with syncope, seizures or sudden death. Whereas someone exhibiting marked prolongation of the QT interval with QTc exceeding 500 ms who was just externally defibrillated from torsades de pointes while swimming poses negligible diagnostic challenge as to the unequivocal probability of LQTS, the certainty is considerably less for the otherwise asymptomatic person who happens to host a QTc value coined “borderline” (QTc ⩾440 ms). Although a normal QT interval imparts a much lower risk of life-threatening events, it does not preclude a patient from nevertheless harbouring a potentially lethal LQTS-causing genetic mutation. Indeed, genetic testing exerts significant diagnostic, prognostic and therapeutic implications. However, the 12-lead ECG remains the universal initial diagnostic test in the evaluation of LQTS and is subject to miscalculation, misinterpretation and mishandling. This review discusses the components of accurate QTc measurement and diagnosis, re-examines what is known about factors affecting QT interval measurement, and clarifies current recommendations regarding diagnosis of so-called “borderline” QT interval prolongation. The current guideline recommendations for the athlete with LQTS are also summarised.

[1]  H. Bazett,et al.  AN ANALYSIS OF THE TIME‐RELATIONS OF ELECTROCARDIOGRAMS. , 1997 .

[2]  A. Jervell,et al.  CONGENITAL DEAF‐MUTISM, FUNCTIONAL HEART DISEASE WITH PROLONGATION OF THE Q‐T INTERVAL, AND SUDDEN DEATH , 1999, American heart journal.

[3]  G. Gemme,et al.  [RARE CARDIAC ARRYTHMIAS OF THE PEDIATRIC AGE. II. SYNCOPAL ATTACKS DUE TO PAROXYSMAL VENTRICULAR FIBRILLATION. (PRESENTATION OF 1ST CASE IN ITALIAN PEDIATRIC LITERATURE)]. , 1963, La Clinica pediatrica.

[4]  Ward Oc.  A NEW FAMILIAL CARDIAC SYNDROME IN CHILDREN. , 1964 .

[5]  O. C. Ward.  A NEW FAMILIAL CARDIAC SYNDROME IN CHILDREN. , 1964, Journal of the Irish Medical Association.

[6]  References , 1971 .

[7]  S. Talbot.  QT interval in right and left bundle-branch block. , 1973, British heart journal.

[8]  E. Prystowsky,et al.  Prolongation of the Q-T interval in man during sleep. , 1983, The American journal of cardiology.

[9]  P. Schwartz,et al.  Idiopathic long QT syndrome: progress and questions. , 1985, American heart journal.

[10]  A J Moss,et al.  Electrocardiographic quantitation of ventricular repolarization. , 1989, Circulation.

[11]  M. Leppert,et al.  The spectrum of symptoms and QT intervals in carriers of the gene for the long-QT syndrome. , 1992, The New England journal of medicine.

[12]  D. Levy,et al.  An improved method for adjusting the QT interval for heart rate (the Framingham Heart Study) , 1992, The American journal of cardiology.

[13]  Peter J. Schwartz,et al.  Diagnostic Criteria for the Long QT Syndrome An Update , 1993, Circulation.

[14]  A. Moss,et al.  Calculation of QTc duration and variability in the presence of sinus arrhythmia. , 1995, The American journal of cardiology.

[15]  A. Moss,et al.  ECG T-wave patterns in genetically distinct forms of the hereditary long QT syndrome. , 1995, Circulation.

[16]  Morrison Hodges,et al.  Rate Correction of the QT Interval , 1997 .

[17]  E. Rosenthal,et al.  Prolongation of the QT interval and the sudden infant death syndrome. , 1998, The New England journal of medicine.

[18]  M J Ackerman,et al.  The long QT syndrome: ion channel diseases of the heart. , 1998, Mayo Clinic proceedings.

[19]  L. Bankir,et al.  mRNA Expression of Renal Urea Transporters in Normal and Brattleboro Rats: Effect of Dietary Protein Intake , 1999, Nephron Experimental Nephrology.

[20]  P. Davey,et al.  A new physiological method for heart rate correction of the QT interval , 1999, Heart.

[21]  S. Priori,et al.  Low penetrance in the long-QT syndrome: clinical impact. , 1999, Circulation.

[22]  G. Vincent,et al.  The inherited long QT syndrome: from ion channel to bedside. , 1999, Cardiology in review.

[23]  W. Allan,et al.  Long QT Syndrome , 1998, Pediatrics.

[24]  X. Jouven,et al.  Relation between QT duration and maximal wall thickness in familial hypertrophic cardiomyopathy , 2002, Heart.

[25]  Michael J Ackerman,et al.  Sex-Selective QT Prolongation During Rapid Eye Movement Sleep , 2002, Circulation.

[26]  A. Gramolini,et al.  Ankyrin-B mutation causes type 4 long-QT cardiac arrhythmia and sudden cardiac death , 2003, Nature.

[27]  M. Ackerman,et al.  Cardiac channelopathies: it's in the genes , 2004, Nature Medicine.

[28]  W. Brady,et al.  Electrocardiographic manifestations: electrolyte abnormalities. , 2004, The Journal of emergency medicine.

[29]  Li Zhang,et al.  Inaccurate electrocardiographic interpretation of long QT: the majority of physicians cannot recognize a long QT when they see one. , 2005, Heart rhythm.

[30]  G. V. Van Hare,et al.  Task Force 7: arrhythmias. , 2005, Journal of the American College of Cardiology.

[31]  C. Wren.  Cardiovascular pre-participation screening of young competitive athletes for prevention of sudden death: proposal for a common European protocol. , 2005, European heart journal.

[32]  S. Priori,et al.  Long QT syndrome and short QT syndrome: how to make correct diagnosis and what about eligibility for sports activity , 2006, Journal of cardiovascular medicine.

[33]  Pietro Delise,et al.  Recommendations for participation in leisure-time physical activity and competitive sports of patients with arrhythmias and potentially arrhythmogenic conditions Part II: Ventricular arrhythmias, channelopathies and implantable defibrillators , 2006, European journal of cardiovascular prevention and rehabilitation : official journal of the European Society of Cardiology, Working Groups on Epidemiology & Prevention and Cardiac Rehabilitation and Exercise Physiology.

[34]  Michael J Ackerman,et al.  Mutant Caveolin-3 Induces Persistent Late Sodium Current and Is Associated With Long-QT Syndrome , 2006, Circulation.

[35]  M. Dubik.  Screening for Long QT Syndrome , 2006 .

[36]  Maurizio Schiavon,et al.  Trends in sudden cardiovascular death in young competitive athletes after implementation of a preparticipation screening program. , 2006, JAMA.

[37]  D. Tester,et al.  Effect of clinical phenotype on yield of long QT syndrome genetic testing. , 2006, Journal of the American College of Cardiology.

[38]  A. Moss,et al.  QT Interval: How to Measure It and What Is “Normal” , 2006, Journal of cardiovascular electrophysiology.

[39]  S. Priori,et al.  Cost-effectiveness of neonatal ECG screening for the long QT syndrome. , 2006, European heart journal.

[40]  M. Ackerman,et al.  Epinephrine QT Stress Testing in the Evaluation of Congenital Long-QT Syndrome: Diagnostic Accuracy of the Paradoxical QT Response , 2005, Circulation.

[41]  Michael J. Ackerman,et al.  Mutation of an A-kinase-anchoring protein causes long-QT syndrome , 2007, Proceedings of the National Academy of Sciences.

[42]  V. Vetter.  Clues or miscues? How to make the right interpretation and correctly diagnose long-QT syndrome. , 2007, Circulation.

[43]  D. Tester,et al.  Diagnostic Miscues in Congenital Long-QT Syndrome , 2007, Circulation.

[44]  Elijah Behr,et al.  Prevalence and significance of an isolated long QT interval in elite athletes. , 2008, European heart journal.

[45]  Michael J Ackerman,et al.  SCN4B-Encoded Sodium Channel &bgr;4 Subunit in Congenital Long-QT Syndrome , 2007, Circulation.

[46]  S. Krishnan,et al.  Prolongation of the QTc interval is seen uniformly during early transmural ischemia. , 2007, Journal of the American College of Cardiology.

[47]  R. Kovacs,et al.  Heart rate-corrected QT interval in men increases during winter months. , 2007, Heart rhythm.

[48]  A. Moss,et al.  Congenital long QT syndrome: considerations for primary care physicians. , 2008, Cleveland Clinic journal of medicine.

[49]  A. Barkus,et al.  A meta-analysis of heart rate and QT interval alteration in anorexia nervosa , 2008, The world journal of biological psychiatry : the official journal of the World Federation of Societies of Biological Psychiatry.

[50]  Arthur A M Wilde,et al.  Accurate electrocardiographic assessment of the QT interval: teach the tangent. , 2008, Heart rhythm.

[51]  D. Tester,et al.  Syntrophin mutation associated with long QT syndrome through activation of the nNOS–SCN5A macromolecular complex , 2008, Proceedings of the National Academy of Sciences.

[52]  J. Marcin,et al.  Prolonged QT interval corrected for heart rate during diabetic ketoacidosis in children. , 2008, Archives of pediatrics & adolescent medicine.

[53]  E. W. Hancock,et al.  AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the , 2009, Circulation.

[54]  E. W. Hancock,et al.  AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the , 2009, Journal of the American College of Cardiology.

[55]  G. Andrassy,et al.  Prolonged QT interval corrected for heart rate during diabetic ketoacidosis in children: psychological stress could be another explanation. , 2009, Archives of pediatrics & adolescent medicine.