“Not so wide” QRS tachycardia: Isn’t it a VT?

Mid Term ISECON, Thane, Nov 2017

Satish Toal

Director Cardiac Electrophysiology, New Brunswick Heart Centre,

Asst Prof., Dept of Medicine, Dalhousie University

Disclosures

•No conflict of interest

Objectives:

• Identify narrow and “not so wide” QRS tachycardia that can be VT • Identify features on ECG that help diagnose them •Understand acute and long term management of fascicular VT

ARE THE QRS NARROW OR WIDE

•Cannot tell conclusively from a single monitor strip

•Get a 12 lead ECG, if clinically possible

•QRSd < 120 ms is narrow, < 145 ms relatively narrow

•Common things common - narrow complex rhythms are more likely to be supraventricular and wide complex ventricular

•Remember arrhythmias can break rules - exceptions to both can happen

•Acute treatment – usually don’t have to break our rules !

•Than why bother?

• Important for long term management and prognosis

• Idiopathic Fascicular VT

•VT post MI using His Purkinjee system or propagating into it very early

•Children (with a narrower baseline QRS in sinus rhythm)

•Digoxin toxicity - mechanism is enhanced automaticity in the region of the fascicles

Narrow Complex tachycardias that can be VT are unusual

History

•34 year male

•H/o palpitations, previous ER visits

•Not feeling well for few days

•No h/o structural heart disease

•Normal echo

After beta blockers in previous admission

Most common idiopathic VT of the left ventricle.

It is a re-entrant tachycardia, typically seen in young patients without structural heart disease.

Only 10% of cases of VT occur in the absence of structural heart disease, termed idiopathic VT. The majority of idiopathic VTs (75-90%) arise from the right ventricle — e.g right ventricular outflow tract tachycardia.

Fascicular VT is the most common type of idiopathic VT arising from the left ventricle (10-15% of all idiopathic VTs).

Usually occurs in young healthy patients (15-40 years of age; 60-80% male). Most episodes occur at rest but may be triggered by exercise, stress and beta agonists. The mechanism is re-entrant tachycardia due to an ectopic focus within the left ventricle.

A similar ECG pattern of fascicular VT may occur with digoxin toxicity, but here the mechanism is enhanced automaticity in the region of the fascicles.

Fascicular VT

Monomorphic ventricular tachycardia eg. fusion complexes, AV dissociation, capture beats.

QRS duration 100 – 140 ms — this is narrower than other forms of VT.

Short RS interval (onset of R to nadir of S wave) of 60-80 ms — the RS interval is usually > 100 ms in other types of VT.

RBBB Pattern.

Axis deviation depending on anatomical site of re-entry circuit (see classification). ◦ Posterior fascicular VT (90-95% of cases): RBBB morphology + left axis deviation; arises close

to the left posterior fascicle. ◦ Anterior fascicular VT (5-10% of cases): RBBB morphology + right axis deviation; arises close to

the left anterior fascicle. ◦ Upper septal fascicular VT (rare): atypical morphology – usually RBBB but may resemble LBBB

instead; cases with narrow QRS and normal axis have also been reported. Arises from the region of the upper septum

Fascicular VT

After ablation – pt comes back

Comes back again after “successful” ablation !

Figure 2

HeartRhythm Case Reports 2016 2, 101-106DOI: (10.1016/j.hrcr.2015.11.011)

Copyright © 2016 Heart Rhythm Society Terms and Conditions

• Diagnosis can be difficult and this rhythm is often misdiagnosed as SVT with RBBB;

• Use criteria other than QRS duration for diagnosis: • Characteristic pattern of QRS morphology

• Capture beats,

• Fusion beats,

• VA dissociation – remember there may be exceptions

• Never forget the clinical setting – • History

• Age,

• Structural heart disease

• Medications

Diagnosis – fascicular VT

• Often unresponsive to adensoine, vagal maneouvers, and lidnocaine.

• However, it characteristically responds to verapamil.

• Digoxin-induced fascicular VT is responsive to Digoxin Immune Fab.

Management – fascicular VT Arrhythmia may break rules, do you?

Recent AWMI, tachycardia 190 bpm, QRSd 110 ms

Miller JM. The many manifestation of ventricular tachycardia. J Cardiovasc Electrophysiol. 1992;3:88-107.

Miller JM. The many manifestation of ventricular tachycardia. J Cardiovasc Electrophysiol. 1992;3:88-107.

RBBB, Left axis, QRSd 135 ms

Bogun F, Good E, Reich S, et al. Role of Purkinje fibers in post-infarction ventricular tachycardia. J Am Coll Cardiol. 2006;48:2500–2507

Narrow QRS VT post MI

• Abello et al - incidence of SMVT with a QRS complex <140 ms in patients with a prior MI was 5.9%.

• Miller et al reported an incidence of 12% N-SMVT (<0.14 s) in a series of patients with SMVT.

• Hayes et al described an incidence of N-SMVT (<0.11 s) of 4.7%.

• A short QRS complex duration is attributed to a circuit exit of the N-SMVT in the proximity of the interventricular septum.

• Bogun et al described the presence of a shared isthmus in some 40% of post-MI SMVT.7

• Purkinje fibers may participate in the re-entry circuit of post-infarction VT.

• Involvement of the Purkinje system accounts for the relatively narrow QRS complexes (≤145 ms) during these VTs. Usually have RBBB morphology

• VT with left bundle branch block morphology, the effective target site was near the His bundle - suggesting that a proximal portion of the His-Purkinje system, before the branch point of the right and left bundle branches, was involved.

•

Bogun F, Good E, Reich S, et al. Role of Purkinje fibers in post-infarction ventricular tachycardia. J Am Coll Cardiol. 2006;48:2500–2507

Bogun F, Good E, Reich S, et al. Role of Purkinje fibers in post-infarction ventricular tachycardia. J Am Coll Cardiol. 2006;48:2500–2507

• 61 year male, HTN, DM

• No previous heart disease

• Normal coronaries

• Mild global LV dysfunction

• Hemodynamically stable

• IV adenosine – no effect

• Spontaneous termination but repeated runs

• Given metoprolol, Verapamil – no effect

• Responded to fleicanide !

Al’Aref et al Differentiation of Left Ventricular Arrhythmias Circ Arrhythm Electrophysiol.2015;8:616-624. DOI: 10.1161/CIRCEP.114.002619

Take home message • Narrow complex VT can happen, but are uncommon, hence rule out SVT • Don’t just focus on QRS width • Analyze ECG completely - morphology, axis, VA association, capture/fusion

beats • Correlate ECG with clinical scenario • If pt has h/o MI

• Look for capture, fusion beats, VA dissociation

• If young healthy pt • Look for characteristic RBBB left axis deviation in addition to capture, fusion beats and

VA dissociation

• Treatment: • Fascicular VT responds to Verapamil. • Post MI pts always consider possibility of VT with sustained monomorphic tachycardia

in relatively narrow QRS • Digoxin-induced fascicular VT is responsive to Digoxin Immune Fab.