Authored by Dr Francesca Finch (FY2 doctor, John Radcliffe hospital Oxford)
HPC: A 35 year old woman was admitted with a 2 day history of palpitations associated with intermittent dizziness. Her symptoms started suddenly when she was working at her desk. She did not experience any chest pain. Observations were stable throughout.
She had a similar episode occurred 6 months previously which was self-limiting, for which she did not seek medical attention.
She is normally fit and well, with no significant past medical history or regular medications.
Blood tests were all within normal range, and bedside ECHO showed a structurally normal heart.
When looking at this ECG, it is easier to break it down into sections.
In the rhythm strip, there are sections of sinus rhythm (tachycardic) followed by 4 to 5 beats of regular broad complex monomorphic tachycardia. The differential diagnosis of a broad complex tachycardia is supraventricular tachycardia (SVT) with aberrancy, SVT and an accessory pathway, and ventricular tachycardia (VT).
There are also a couple of singular broad QRS complexes, which are ventricular ectopic beats.
Thee fact that the morphology of the ectopics matches the tachycardia make VT most likely. This is a focal type of arrhythmia rather than a rentrant circuit. The focus is either firing once, producing a ventricular ectopic or multiple times, leading to a run of VT.
Next we can see that there is a LBBB morphology, indicated by the dominant S wave in V1 and broad R wave in V5-V6. This shows that the ectopics are the result of a right ventricular origin (if it was a RBBB pattern then it comes from the left ventricle).
Finally, we look at the axis of the abnormal QRS complexes. The QRS complexes are very positive in the inferior leads – the QRS is positive in leads II, III and aVF. This shows us the electrical activity is moving towards the inferior leads (the principle is that if activation is moving away from an ECG lead the QRS is initially and predominantly negative and if it is moving towards it the lead it is positive). In this case it must be originating from the outflow tract of the right ventricle (near the pulmonary valve) which is high up and heading down to the lower part of the ventricle.
Putting this altogether, this is an example of right ventricular outflow tract tachycardia.
A cardiac MRI was performed, which showed non-dilated LV, with borderline impaired systolic function. (LVEF 53). There is a small patch of fibrosis in the region of the basal inferior LV/RV junction. The RV has normal volume and systolic function
Right Ventricular Outflow Tract (RVOT) Tachycardia
Most VTs occur in structurally abnormal hearts. However in 10% of patients with VT, no structural heart disease, metabolic/electrolyte abnormalities or other cause such as long QT syndrome can be found. This type of arrhythmia has been described as idiopathic VT.
Idiopathic VTs can originate from multiple anatomical regions, including the left ventricular outflow tract (LVOT) and right ventricular outflow tract (RVOT), the left fascicular system, the mitral and tricuspid annuli, and the papillary muscles, or they can develop in the epicardial space. More than half of all idiopathic VTs originate from the outflow tracts (OTs), and of these, approximately 80% originate from the RVOT
Commonly occuring symptoms include palpitations, chest pain, dyspnoea, and light-headedness during episodes . Syncope can occur rarely. However some patients may have only fatigue or may be entirely asymptomatic
In general RVOT VTs have a good and benign prognosis. Treatment is tailored on an individual basis depending on the nature and severity of symptoms. Pharmacotherapy may include a beta blocker, Verapamil or Diltiazem. Class I (IA and IC) anti-arrhythmic drugs and class III drugs, such as sotalol and amiodarone may also be used. Catheter ablation is considered in cases where pharmacological treatment is not effective or not tolerated.