Makindo Medical Notes

Related Subjects: |ECG-QT interval |Brugada Syndrome |Long QT syndrome (LQTS) Acquired |Long QT syndrome (LQTS) Congenital |Torsades de Pointes |Ventricular Fibrillation |Ventricular Tachycardia |Resuscitation - Adult Tachycardia Algorithm |Automatic Implantable Cardioverter Defibrillator (AICD)

Torsades (Polymorphic VT): Occurs in repetitive Non sustained paroxysms. Can degenerate to VF. Mg 8 mmol (2 g bolus) over 10 mins in 100 ml 5% Dextrose or N-saline. Avoid Amiodarone. Correct K/Mg/Ca. Pacing. Isoprenaline. Defibrillation if unstable.

About

• The term torsade de pointes was coined by Dessertenne in 1966
• A polymorphic ventricular tachycardia with a pattern of twisting points
• Drugs associated with TdP vary greatly in their risk for arrhythmia
• An updated list can be found at www.qtdrugs.org

Definition

• Torsade de Pointes is a polymorphic ventricular tachycardia.
• The axis of the QRS of VT is constantly changing and twisting.
• It is seen with Long QTc > 460 ms.
• Torsade may be due to inhibition of the HERG type potassium channel

Electrocardiogram

Genetics

• Long QT1 have slow potassium channels
• Long QT2 have slow potassium channels
• Long QT3 shows defects in the sodium channels.
• Long QT4-12 are rare
• Congenital long QT syndrome is autosomal dominant, but shows greater frequency of expression and a greater lengthening of the QT interval in females than in their male relatives.

Epidemiology

• Females are 2-3 times more likely to develop TDP.
• Females have more QT prolongation secondary to drug therapy.

Clinical

• Torsade usually but not always occurs in bursts that are not sustained.
• May be well tolerated or cause pulmonary oedema
• Can cause hypotension, presyncope and collapse.
• It may be transient and episodic and cause symptoms and self terminate.
• It may sometimes revert to VF or pulseless VT

Risk factors

• Congenital Romano-ward syndrome (AD)
• Jervell-Lange-Nielsen syndrome (AR Deaf) Female gender
• Acquired long QT syndrome (causes of which include medications and electrolyte disorders such as hypokalaemia, hypocalcaemia, hypomagnesemia)
• Bradycardia, Baseline ECG abnormalities
• Renal or liver failure, Female

Causes of Acquired Long QT

• Low Ca, Low Mg, Low K, hypothyroid, hypothermia
• Amiodarone, Disopyramide, Flecainide, Erythromycin
• Terfenadine, TCA, quinidine, Class I/III antiarrhythmics
• Lithium, Amitriptyline, Chlorpromazine, phenothiazines.
• Check all drugs in BNF

Investigations

• FBC, U&E, Mg, Calcium, Troponin
• ECG: twisting of the QRS axis. Bradycardia and long QTc often QT interval > 500msec and may be increased markedly to = 600 msec
• Troponin may be indicated if ACS suspected
• Echo to exclude structural disease

Management

• Check all drugs in BNF. Stop Amiodarone or other antiarrhythmics that prolong QT. Check and correct K and Mg and Ca
• Polymorphic VT: Magnesium 8 mmol (2 g bolus) over 15 mins diluted in 50-100 ml 5% Dextrose or N-saline. then 72 mmol (18 g) over 24 hrs. The idea is to suppress early afterdepolarizations even in patients with normal magnesium levels
• Overdrive atrial (preferred) or ventricular pacing or just simple pacing if TDP is bradycardia dependent.
• Isoprenaline IV may be considered to suppress arrhythmia. This is contraindicated with congenital long QT syndromes.
• Patients with extreme QT interval prolongation (> 500 msecs) or certain high-risk genotypes should be considered for ICD
• Defibrillation is the treatment of all unstable tachyarrhythmias
• Congenital Long QT: beta-blockers indicated. Left stellate ganglion block may be of value if resistant arrhythmias
• Acquired Long QT: Beta-blockers contraindicated as bradycardia promotes the arrhythmia

References

• Prevention of Torsade de Pointes in Hospital Settings. A Scientific Statement From the American Heart Association and the American College of Cardiology Foundation and on behalf of the American Heart Association Acute Cardiac Care Committee of the Council on Clinical Cardiology, the Council on Cardiovascular Nursing, and the American College of Cardiology Foundation Originally published8 Feb 201