ECG of the Week: ECG of the Week - 8th August 2016

The following ECG's are from an 85yr old female who presented with typical cardiac chest pain at rest. Both the ECG's were performed when the patient was pain free.

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Key features

Ventricular paced rhythm rate 60 bpm
Associated left axis deviation
RsR' pattern in lead V2 rather than typical deep S wave usually seen in RV pacing
Appropriate discordant ST / T wave changes
Sgarbossa negative

Impression

Ventricular paced rhythm
Morphology of leads V1-2 unusual for RV pacing as usually results in typical LBBB morphology
The frontal plane axis is -75 deg with a transition between leads V2-3. These features support correct RV lead placement rather than lead migration and may be seen with inappropriate lead positioning. Seen articles below.
CXR confirmed appropriate pacing lead position

Is RBBB morphology during right ventricular pacing always due to lead malposition ?

The short answer to this is no. There are cases in which an RBBB morphology can occur with appropriate right ventricular apical pacing.

In this case the patient had a chest x-ray which showed appropriate lead placement, for an example of RBBB morphology associated with lead malposition check out this case here.

Features which may assist in differentiating between lead malposition and correct placement are:

Frontal plane axis
Precordial transition point
Repositioning of leads V1-2

I would recommend the following freely available papers which both include a review of RBBB morphology during right ventricular pacing.

Erdogan O, Aksu F. Right bundle branch block pattern during right ventricular permanent pacing: Is it safe or not? Indian Pacing Electrophysiol J. 2007 Aug 1;7(3):187-91. PMID: 17684578 Full text here
Almehairi M, Baranchuk. Right Bundle Branch Block Morphology During Apical Right Ventricular Pacing. The Journal of Innovations in Cardiac Rhythm Management, 4 (2013), 1303–1304. Full text here

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Key features

Sinus rhythm, rate ~60 bpm
PR prolongation
T wave inversion leads II, III, aVF, V4-6

The broad differentials for the changes on the serial ECGs are:

ACS

Structural Heart Disease

Cardiac T-wave Memory

T-wave memory is an interesting phenomenon that could explain the marked T wave changes seen on this ECG. It results in transient T wave changes following a period of abnormal ventricular conduction e.g. ventricular tachycardia, paced rhythms, intermittent bundle branch block or aberrant conduction. There is a recent paper by Vakil that is freely available (linked to below) that contains a nice overview of T-wave memory, proposed mechanisms, and a case example.The deep T wave inversion on this ECG correspond to the leads in which a negative QRS was seen in the patients paced ECG a finding consistent with T-wave memory.

Vakil K, Gandhi S, Abidi KS, et al. Deep T-Wave Inversions: Cardiac Ischemia or Memory? JCvD 2014;2(2):116-118. Full text here.

The patient has negative serial troponins and underwent coronary angiography which showed irregularities only to left main, circumflex and right coronary artery.

References / Further Reading

Textbook