FANS Long QT Syndrome Investigation Protocol (including suspected mutation carriers)

Transcription

1 Clinical Features FANS Long QT Syndrome Investigation Protocol (including suspected mutation carriers) History Syncope or presyncope compatible with ventricular tachyarrhythmia, especially relating to stress or high emotion, physical activity including swimming,, sudden loud noise or at rest or in bed. Congenital deafness is rarely present Exclude other causes of so called acquired LQT eg QT prolonging drugs, electrolyte upset, hypothyroidism, ischaemia. Family History Family members with definite Long QT Syndrome (LQTS). Unexplained premature sudden cardiac death, syncope or seizures among immediate family members. ECG characteristics QT c measured over at least 3 beats in lead II or V5 (whichever is longer) using the tangent method - QT interval is corrected for heart rate using Bazett s formula: QTc=QT RR. Try to obtain the ECG after 5-10mins supine rest and off all drugs that are associated with prolongation of the QT interval, below 60 and above 100 bpm SR gives over and undercorrection respectively by Bazette s. Use Fridericia if over 100 bpm and Framingham if under 60bpm to complement the regular Bazette s calculations

2 (QTc is expressed in ms; the RR interval in the correction factor ( RR) is measured in seconds). If unequivocally normal, should be repeated on 3 separate occasions. QT c 440ms in males, 460ms in females is considered above the majority of normal measurements but may still be part of a normal population see below for full diagnostic criteria Notched T wave in 3 leads. T wave alternans. Associated Arrhythmias Polymorphic Ventricular Tachycardia Torsades de Pointes VF Familial early onset atrial fibrillation Other Cardiac Investigations (to be considered in cases of diagnostic uncertainty) Supine to standing QT stretch QTc prolongs around the time of SR tachy* during standing QT changes described in LQT1, 2 and 3, but most helpful in LQT2 *Sinus Tachycardia Exercise testing QT interval fails to shorten in LQT1. Holter monitoring May identify undue QT prolongation during periods of bradycardia or after ectopics. Adrenaline infusion May paradoxically prolong QT interval in LQT1 (see appendix). Genetics Counselling and consent is mandatory before testing noting the complexities that arise if a variant of unknown significance (VUS) is found. All patients should be discussed with colleagues in Clinical Genetics, within an MDT meeting if possible, prior to testing

3 Diagnostic criteria: As per 2013 LQT guidelines 1) LQT is diagnosed a) LQT risk score of 3.5 in the absence of a secondary cause of Qt prolongation and/or, b) In the presence of an unequivocally pathogenic mutation in one of the LQT genes, or c) In the presence of QTc 500 in repeated 12 lead ECG and in the absence of any secondary causes of Qt prolongation 2) LQTS can be diagnosed in the presence of a QTC ms on repeated ECGs in a patient with unexplained syncope even if there is no pathogenic mutation present and again there is no secondary cause for Qt prolongation Suspected LQTS: Those who are above the 440ms QTC for males and 460ms QTc for females but below the absolute 480ms could have LQT however they may still be part of the normal distribution albeit at the high end. Occasionally those who have an LQT gene can have normal range QTc on their ECG but this is often dependent on the time of day an ECG is done and the capacity of that gene in that individual to be manifest on the ECG Diagnosis of Long QT Syndrome (in the absence of secondary causes for QT prolongation (ESC 2015, page 41, 8.1.1) Recommendations Class a Level b Ref. c LQTs is diagnosed with either: - QTc 480 mn in repeated 12 lead ECG or - LQTs risk score 3 LQTs is diagnosed in presence of confirmed pathogenic LQTS mutation, irrespective of QT duration ECG diagnosis of LQTS should be considered in the presence of QTc 460 ms in repeated 12 lead ECGs in patients with an unexplained syncopal episode in the absence of secondary for QT prolongation I C This panel of experts I C This panel of experts II a C This panel of experts ECG - electrocardiogram; LQTS - long QT syndrome; QTc - corrected QT a - Class of recommendation b - Level of evidence c -Reference(s) supporting recommendations

4 Schwartz Score for the Diagnosis of Long QT Syndrome (1993) Variable Points Electrocardiogram QTc ms* (males) 1 Torsade de pointes 2 T wave alternans 1 T wave notches in 3 leads 1 Bradycardia** 0.5 Clinical history Syncope With stress 2 Without stress 1 Congenital deafness 0.5 Family history*** Family members with confirmed LQTS **** Unexplained sudden death in firstorder family members 30 years *QTc calculated with the formula of Bazett (QTc=QT/RR) **Resting heart rate below the second percentile for age ***The same family member cannot be considered twice ****Schwartz score 4: 1 point: low probability; 2-3 points: intermediate probability; 4 points: high probability References: Postema PG, De Jong J S S G, Van der Bilt I A C, Wilde A A M Accurate electrocardiographic assessment of the QT interval: Teach the tangent. Heart

5 Rhythm 2008; 5: Available electronically at (Log in required). HRS/APHRS/EHRA Expert consensus statement on the diagnosis and management of patients with inherited primary arrhythmia syndromes The phenomenon of QT stunning : The abnormal QT prolongation provoked by standing persists even as the heart rate returns to normal in patients with long QT syndrome Adler A et al Heart Rhythm 2012;9: The Response of the QT Interval to the Brief Tachycardia Provoked by Standing Viskin s et al J Am Coll Cardiol May 4; 55(18): Himeshkumar V, Hejlik J & Ackerman MJ et al. Epinephrine QT stress testing in the evaluation of Congenital Long-QT Syndrome. Circulation 2006; 113: Available electronically at Appendix Adrenaline infusion 0.025mcg/kg/min for 10 minutes, then increased every 5 minutes to 0.05, 0.1 and 0.2 mcg/kg/min with 12 lead ECGs at the end of each stage. (If CPVT is also suspected, the infusion may need to be further increased to 0.3 and 0.4 mcg/kg/min) Stopping criteria include systolic BP>200 mmhg, non-sustained VT or polymorphic VT, >10 VPBs/minute, T wave alternans or patient intolerance. An increase in the QT interval of 30ms or more suggests LQT1 syndrome. Reference Himeshkumar et al