Torsade de pointes or torsades is a Frenchterm that literally means "twisting of thepoints" is a ventricular tachycardia associatedwith a long QT time on the resting ECG. During Torsade de pointes the ventriclesdepolarize in a circular fashion resulting inQRS complexes with a continuously turningheart axis around the baseline (hence thename Torsade de Pointes). It was first described by Dessertenne in 1966 .
Mechanism of Torsades de Pointes Early after depolarizations Transmural reentry
Mechanisms Of Drug - InducedQT Prolongation and Tdp Block of repolarizing K+ currents Stimulation of ICa-l Stimulation of INa
GENE: human ether a go- go related gene. CODES FOR: Ikr MUTATION: STUCTURE:
RISK FACTORS Hypokalemia Severe hypomagnesium Female gender CHF Baseline QT prolongation Congenital long QT syndrome Ventricular arrhythmia Concurrent use of drugs that causes QTprolongation.
Causes of Torsades de Pointes Congenital LQTSJervell Lange Nielsen SyndromeRomano Waed Syndrome Acquired LQTS
Diagnosis First measure the QT interval Secondly, correct it for the heart rate, if heartrate is above 60. Determine if it is greater than 0.5 seconds (500msec) in duration. Lastly, compare QTc to previous QTc’s todetermine if it is lengthening. QTc for man:440ms and females:460ms.
QT Interval• Measure frombeginning of q waveto where the t wavereturns to baseline.• “Rule of thumb” is itShould be less than50% of R-R interval.•If =/> 500 msec 0.50seconds) or > 50% ofR-R interval: risk forTorsades de Pointes!
MANAGEMENT ACUTE CASES:Remove the offending drugCorrect K,Mg levelsMg: doc-in suspected EADsdose:1-2g initially given in 30-60secsrepeat every 5-15min alternativelyMOA:K: MOA: rapid repolarisation.LIDOCAINE:
MEXILITINE: ISOPROTERENOL:MOA:Indication:C/I: TEMPORARY TRANSVENOUS PACING:Atrial pacing preferredPacing at 90-110bpm until QT is normal. IF Tdp does not terminate spontaneously:
LONG TERM MANAGEMENT:Beta blockers: PropranololEsmolol,NadololLimitations:SCD can occurLong term complianceS/E:IMPLANTABLE CARDIOVERTERDEFIBRILLATOR:Indications: Patients with VT,VF,abortedcardiac arrest.used with beta blockers.
Management of congenital long QTsyndrome:Beta blockers:ICDs: Prevention of drug induced Tdps:
RECENT ADVANCES:Genetic testing for carriers of long QT syndrome:FAMILION LQTS TEST:USES: NOVELTHERAPY: Sodium channel blockersCCBsAtropineProtien kinase inhibitorsAlpha blockersPotassium chanl.openers
Drug Induced QT ProlongationPreclinical Screeing In vitro APD effectsIsolated myocytes(dog,rabbit,g. pig)Purkinje fibers (dog,rabbit)Papillary muscle (guinea pig) In vivo modelsConscious rabbitConcious HypokalemicdogsCanine models with