Thursday, March 6, 2014

ECG Interpretation Review #85 (Aberration – Left Anterior Hemiblock – Fascicular VT – Typical RBBB – WCT)

     The ECG and lead II rhythm strip shown in Figure-1 — was obtained from a 23-year old man who presented with “palpitations”. He was presumably healthy prior to the occurrence of this arrhythmia — and he was hemodynamically stable at the time this ECG was recorded.
  • Is the rhythm more likely to be VT (Ventricular Tachycardia) or SVT (SupraVentricular Tachycardia) with aberrant conduction?
  • What factors favor one or the other diagnosis?
  • Adenosine was initially tried as treatment. When this was unsuccessful — Verapamil was tried. Comment on this selection of treatment.
Figure-1: ECG and lead II rhythm strip obtained from a 23-year old male with palpitations. He is hemodynamically stable. Is this more likely to be VT or SVT with aberration? NOTE — Enlarge by clicking on Figures — Right-Click to open in a separate window.
------------------------------------------
Interpretation of Figure-1: The rhythm appears to be a regular WCT (Wide-Complex Tachycardia). Unfortunately, angling of the ECG paper has introduced slight irregularity in measured intervals — but the “theme” of this smart phone photo is that of a regular WCT rhythm.
  • The rate of this regular WCT is just over 200/minute.
  • The QRS complex is wide. QRS morphology resembles the bifascicular block pattern of RBBB (Right Bundle Branch Block) with LAHB (Left Anterior HemiBlock).
  • No P waves are seen.
Assessment: The differential diagnosis of a regular WCT rhythm without sinus P waves should always be, “VT until proven otherwise”. The patient should be treated accordingly. Statistically — at least 80-90% of such cases will be VT (especially if the patient is an older adult with a history of underlying heart disease). That said — there are a number of unique aspects to this case.
  • This patient was not an “older adult with underlying heart disease”. Instead — he was a presumably healthy young adult who presented with palpitations, but who was hemodynamically stable. Certain types of VT rhythms are known to occur in a younger adult age group in the absence of underlying heart disease. Many of these rhythms are catecholamine-related and exercise-induced. A significant percentage of these VT rhythms (thought to account for up to 5-10% of all VT rhythms) are adenosine responsive — which is one reason in support of early trial of adenosine in the treatment approach to a regular WCT of uncertain etiology. In addition to young age of the patient and absence of underlying heart disease — certain ECG features sometimes clue the provider in to the likelihood that one of these special forms of VT may be operative (See discussion on RVOT VT in our ECG Blog #35).
Although VT should be presumed until proven otherwise for the regular WCT rhythm in Figure 1 — there is a possibility that QRS widening could instead be due to: i) Preexisting BBB (Bundle Branch Block); or ii) Aberrant conduction. That said — We feel neither is likely in this case.
  • Our reason for stating this is the clear absence of “typical” RBBB morphology in lead V1 of Figure-1. Normally with RBBB — there should be an rSR’ complex in lead V1 with: i) S wave that descends to slightly below the baseline; and ii) A taller right “rabbit ear” (= R’ that is slender and taller than the initial positive component in lead V1). These same morphologic features of “typical” RBBB when seen in a patient with a WCT rhythm may also suggest aberrant conduction (Panel A and Panel B in Figure-2).
  • In contrast — atypical QRS morphology in lead V1 is far less likely to be due to RBBB or aberrant conduction (Panels C, D, E and F in Figure-2). While atypical QRS morphology in lead V1 may clearly occur with RBBB in patients with ischemic heart disease, scarring from cardiomyopathy and/or RVH — one would expect an otherwise healthy young adult to manifest a fairly typical RBBB pattern (as in Panel A or B in Figure-2) — IF the reason for QRS widening was simple RBBB.
Figure-2: Use of QRS morphology in a right-sided lead (V1 or MCL-1) to distinguish between ventricular ectopy (including VTvs aberrant conduction. Only a typical RBBB pattern (rsR’ with descent of S wave below the baseline and with terminal taller right rabbit ear) is predictive of aberration (A or B). Any other pattern (C, D, E, F ) predicts ventricular ectopy. (Figure reproduced from ACLS-2013-ePub).
------------------------------------------
Follow-Up:
     The clinical presentation and ECG features shown in Figure-1 for this case are most suggestive of Fascicular VT as the reason for QRS widening This is because:
  1. The patient is a 23-year old man who was previously healthy — and who presented with palpitations in a hemodynamically stable condition (ie, an unlikely scenario for an ischemic form of VT).
  2. Despite superficial resemblance to a bifascicular block pattern of RBBB/LAHB — QRS morphology in lead V1 is clearly atypical for RBBB since: a) the S wave does not descend to below the baseline; and b) the R’ is far wider than is usually seen for typical RBBB.
     This patient was initially treated with Adenosine. There was no response. Verapamil was then given. Spontaneous conversion to sinus rhythm occurred a short while later.
  • We emphasize that the calcium blockers Verapamil and Diltiazem are contraindicated for treatment of ischemic VT. In a patient with ischemic VT who is only tolerating the arrhythmia because of compensatory vasoconstriction — the vasodilatory and negative inotropic properties of Verapamil/Diltiazem are likely to precipitate acute deterioration. Surprisingly — fascicular VT often responds to calcium blockers. While not advocating empiric use of calcium antagonists for WCT rhythms until definitive diagnosis of fascicular VT is made — this treatment was effective in this case.
  • When in doubt — Cardioversion is the safest treatment for WCT rhythms not responding to trial of medication. Referral to EP (ElectroPhysiology) is indicated for further assessment and consideration of ablative therapy in this case.
  • For more details on Fascicular VT – Please see our ECG Blog #38 -
------------------------------------------
Acknowledgment: My appreciation to Ong Jiann Ruey – who contributed the case and the tracing shown in Figure 1.
------------------------------------------