ECG Case 119

On first glance this may appear to be SVT with LBBB as there is:

• Regular broad-complex tachycardia, rate 174
• Typical LBBB morphology in aVR, V1 and V6
• Absence of fusion or capture beats

However, there is one feature here that is unusual for LBBB, can you spot it?

In addition, there are other features suggestive of VT, can you spot them?

Reveal answer

There are signs of AV dissociation, with P waves discernible at different rates to QRS complexes (sensitivity 82%, specificity 98%):

The initial R wave in V1 measures ~40ms:

• With a dominant S wave in V1, an initial R wave of > 30-40ms is also suggestive of VT (Brugada algorithm)

The differential diagnosis of a regular broad complex tachycardia is VT versus SVT with aberrant conduction (due to bundle branch block or Wolff-Parkinson-White Syndrome). For an in-depth review of differentiating between the two, see VT versus SVT.

RVOT tachycardia is a form of monomorphic VT originating from the outflow tract of the right ventricle or occasionally from the tricuspid annulus. It is most commonly a form of idiopathic VT, whereby no structural heart disease, metabolic/electrolyte abnormalities, or long QT syndrome can be found. It can also be seen in patients with Arrhythmogenic Right Ventricular Dysplasia (ARVD).

The RVOT is divided into rightward (free wall), anterior, leftward, and posterior (septal) parts. RVOT tachycardia can originate from any of these sites but all carry common ECG characteristics.

ECG features of RVOT VT:

Other general features of VT, such as AV dissociation, fusion and/or capture beats may also be present.

If the patient is stable, you can administer adenosine…

• Acute termination of idiopathic RVOT VT in a stable patient can be achieved by vagal manoeuvres or adenosine (6mg up to 24mg)
• IV verapamil is an alternative if the patient has adequate blood pressure
• DCCV is always the management preference if there is haemodynamic instability.

RVOT tachycardia in ARVD generally does not terminate with adenosine. Differentiation between idiopathic RVOT tachycardia and that caused by ARVD can be difficult and may rely on previous ECG findings as well as family history. In ARVD, the baseline ECG usually shows inverted T waves in right precordial leads, and when present, RV conduction delay with an epsilon wave best seen in V1-2.