Dr. smith’s ecg blog palpitations of unusual etiology electricity in the body causes


This shows sinus rhythm with RBBB. There is no LPFB present on this ECG. So the RBBB seen on the presentation ECG is already present at baseline, however the LPFB was not. This feature does not help distinguish between SVT with RBBB and LPFB vs. fascicular VT originating in the left anterior fascicle, because it is still possible to have a rate-related LPFB in the setting of SVT with preexisting RBBB.

The patient underwent an electrophysiology study, during which Bundle Branch Reentrant Ventricular Tachycardia (BBRVT) was reproduced and successfully ablated. He received an AICD, also underwent a cath showing non obstructive disease and cardiac MRI without abnormalities.

Bundle Branch Reentrant Ventricular Tachycardia is a rare arrhythmia involving components of the infra-His conduction system (including the three fascicles themselves) as necessary components of a reentrant pathway. As you would expect, there are different ways to combine these circuit limbs, all of which would create different reentrant loops and different QRS morphologies.

Tchou and Mehdirad have been credited with describing three categories of BBRVT (see diagram below). Because our patient’s QRS morphology includes RBBB and LPFB, this may be consistent with Type B, which appears to use one of the LBB fascicles anterogradely and the other retrogradely to comprise the reentry loop. If the circuit were to progress anterogradely down the LAF and retrogradely up the LPF, it would theoretically have the appearance of RBBB with LPFB, matching our patient.

There are other matching possibilities, however, including Type C with additional rate-related LPFB. At some point, enumerating these possibilities becomes purely academic because they do not have implications for prospective clinical management.

If these reentrant tachycardias are particularly sensitive to any medications, I am not yet aware of it. I cannot find any evidence stating that BBRVTs typically respond to any particular medication with any reliability. The few publications that do comment on pharmacologic therapy in the acute arrhythmic phase seem to agree that pharmacologic therapy is usually ineffective. Because they exist in the conduction system below the AV node, I would not expect that they should respond to AV nodal blockade such as adenosine.

Apparently BBRVT is highly associated with structural heart disease and cardiomyopathy in most cases, but more rarely has been described in the absence of structural heart disease (which our patient seems to fall into, except for his baseline RBBB). This further highlights the importance of considering bedside US for LV function before considering verapamil in these cases.

DDx includes classic VT vs. SVT+RBBB+LAFB vs. posterior fascicle VT vs. BBRVT vs. (probably other even more rare and obscure rhythms); if you believe it is one of the ventricular causes but not classic VT, then posterior fascicle VT seems to be one of the most common, and it is typically verapamil sensitive. Electricity works.

DDx includes classic VT vs. SVT+RBBB+LPFB vs. anterior fascicle VT vs. BBRVT vs. (who knows what else); if you believe it is one of the ventricular causes but not classic VT, then anterior fascicle VT is possible and may be verapamil sensitive, but it may not be; the pharmacologic solutions are unknown in this category. Electricity works.

DDx includes classic VT vs. SVT+LBBB vs. RVOT VT vs. BBRVT vs. (probably others). If you believe it is one of the ventricular causes but not classic VT, then RVOT VT is possible and is typically adenosine sensitive (and adenosine is already indicated for a stable patient with monomorphic wide complex tachycardia). Electricity works.

With experience and training, one can recognize wide QRS complexes which are likely to represent VT originating within the conduction system itself. Unfortunately, this category still includes a wide variety of arrhythmias which differ in their mechanisms and effective medications. Perhaps the only universal truth is that they are all susceptible to electrical cardioversion.

BBRVT is a rare arrhythmia which originates inside the ventricular conduction system and acts similarly to other fascicular VTs we have discussed on this blog. However, there do not appear to be any clear patterns of response to pharmacologic therapy.

Excellent case! As per Drs. Meyers & Smith — QRS morphology in ECG #1 resembles RBBB/LPHB, but is atypical because of the taller-left-rabbit-ear and lack of distinct S wave for the complex in lead V1. If this rhythm in ECG #1 was supraventricular (and not VT), with QRS widening due to either preexisting rbbb/lphb or aberrant conduction — then some form of underlying heart disease would seem likely given how atypical for rbbb the QRS morphology is in lead V1 of ECG #1. That said, definitive distinction between SVT vs VT is simply not possible from this 1st ECG alone. Of interest, the post cardioversion tracing ( = ECG #2) would seem to strongly favor some form of VT as the etiology — because: i) While still showing a RBBB pattern in lead V1 — the QR morphology in ECG #2 is different than the more monophasic morphology in V1 of ECG #1; and ii) There is suggestion of LAHB + RBBB in ECG #2 — and it would seem unlikely to develop a rate-related LPHB, while at the same time losing a baseline LAHB because of the rate increase … THANKS again to Drs. Meyers & Smith for insight into the entity of Bundle Branch Reentrant VT. Reply Delete

Agree — I think it difficult to be sure if the notching we are seeing in the mid-part of the ST-T wave in lead II during the tachycardia represents retrograde atrial activity. It looks like similar atrial activity (at about the same point in the ST-T wave) is seen in lead aVR, and possibly in V1,V2 … That said — this clearly is not a sinus P wave (as per Pendell) — and if this does in fact represent 1:1 retrograde VA activity — this is of NO help in distinction between SVT vs VT — because both reentry SVT as well as VT may conduct retrograde with 1:1 VA activity. Normally, I compare the tachycardia tracing with the post-sinus rhythm conversion tracing when trying to “retrospectively” determine IF “notching” seen during tachycardia was in fact reflective of atrial activity during the tachycardia — BUT — in this case, since the rhythm was VT and QRS morphology of the RBBB pattern after conversion to sinus rhythm DIFFERS from QRS morphology during VT — one cannot compare QRS morphology in the 2 tracings. All one can say is that even in the baseline RBBB pattern during sinus rhythm — that there is considerable fragmentation of the QRS (despite apparent lack of underlying heart disease suggested by the normal cath). Delete

As per Pendell, input from an electrophysiologist (ideally, the very electrophysiologist on this case) would be optimal — to ensure there are no considerations that we may be missing. My impressions had been that risk depended most on: i) the presence and severity of underlying heart disease; and ii) the frequency and severity (ie, duration and associated hemodynamic consequences) of the arrhythmia in question. It sounds like in this case that this patient WAS fully evaluated (including cardiac cath) — and was NOT found to have any underlying heart disease. As to the arrhythmia — it would seem that IF the patient initially had a spontaneous and/or easily inducible tachyarrhythmia (which was VT in this case) — but that IF after ablation, no arrhythmia was now inducible — that risk of recurrence should (in theory) have been eliminated — in which case you are correct to wonder about whether an ICD was truly needed ??? Again — comment from the electrophysiologist who participated in this case is the only way to know if we are missing something here … Reply Delete