Ventricular Tachycardia                                                                      

Presentation

Ventricular tachycardia (VT) is an unusual arrhythmia in pediatric patients. It may present with signs of cardiac failure, cardiovascular collapse or near miss sudden death.

Reentrant Ventricular Tachycardia

Reentrant VT is the usual mechanism in late postoperative disease and those with cardiomyopathy. The underlying substrate being scar tissue if there has been a ventriculotomy,  abnormal ventricular loading conditions and/or abnormal myocyte arrangements (eg hypertrophic cardiomyopathy).

 It can be a difficult arrhythmia to manage and if possible the underlying haemodynamic problem should be addressed.  Many antiarrhythmic drugs have a pro-arrhythmia potential for example cardiomyopathy in adults it has been shown that some drugs eg flecainide may actually increase the risk of life threatening arrhythmias. An exception may be amioderone and this may be the drug of choice in reentrant VT.

Long QT Syndrome (LQTS)

This diagnosis is based upon a scoring system devised by Schwartz (Current Problems in Cardiology: The Long QT Syndrome. Mosby: Volume 22 Number 6 Pages 297-352) which takes into account the history, family history and ECG findings - rate, morphology and corrected QT interval. The inheritance is autosomal dominant with incomplete penetrance.

There are different clinical subtypes which are now recognised to be due to different molecular deletions in various chromosomes. The common theme is an abnormality in the sodium and potassium channels in the myocyte prolonging the action potential. The precise arrhythmia initiation mechanism however still remains uncertain. The characteristic VT pattern is called torsades de pointes as the complexes appear to rotate around the axis.

The mainstay of therapy is propranolol or nadolol. If this fails then left cervical sympathectomy is indicated. Finally implantable defibrillators have a role in very severe cases. Avoidance of drugs that prolong the QT interval is also important (macrolide antibiotics, non sedating antihistamines etc). An up to date list is kept by Georgetown University. Some patients (type LQT1) are prone to VT during stress or exercise and sporting restrictions are necessary.

There is an excellent website for physicians and families (QT Syndrome.ch) with additional information.

Junctional Ectopic Tachycardia

This is also called nodal tachycardia, His bundle tachycardia or automatic junctional tachycardia. It is relatively common in the acute postoperative period (particularly following tetralogy of Fallot repair) but may also present with cardiac failure secondary to a tachycardia induced cardiomyopathy in the first few months of life.

The ECG shows a rapid, narrow complex tachycardia and there is usually haemodynamic compromise. The diagnostic hallmark is AV dissociation.

ECG recording above right uses temporary atrial wires post surgery. The small sharp spikes are p waves and the broad complexes QRS waves. Note that the ventricular rate is quicker than the atrial rate and their is A-V dissociation.

The management in the acute postoperative period includes overdrive pacing, active cooling to 35°C and an amioderone infusion. Provided these measures improve the cardiac output the JET usually resolves and is not a long term problem.

For those presenting in infancy many are resistant to both β blockers and amioderone and the mortality can be high. Radiofrequency ablation of the automatic focus can be attempted but if it fails ablation of the AV node and permanent pacing is necessary.

This page was last edited 14/2/2004