An ECG in Disguise?
By Ken Grauer, MD
The electrocardiogram (ECG) in the figure was recorded from an older man following a bradycardic and hypotensive episode. What ECG diagnosis is suggested by this tracing? What are the clinical implications of this diagnosis? Hint: What type of bundle branch block is present?
Interpretation: The initial rhythm in today’s tracing is sinus tachycardia at a rate of ~115 beats/minute.
- The QRS complex is wide. QRS morphology in the chest leads is consistent with right bundle branch block (RBBB) — as seen by the predominantly upright (qR) pattern in right-sided lead V1, with a positive R wave and a wide terminal S wave in left-sided lead V6.
- In contrast, the wide QRS seen in the limb leads suggests left bundle branch block (LBBB), given the all upright R wave in lead aVL and the almost all upright R wave in left-sided lead I. The frontal plane axis is decidedly leftward (i.e., with predominantly negative QRS complexes in each of the inferior leads).
- ST-T waves show some flattening and ST-T wave depression that does not look acute and is not unexpected given the pattern of QRS widening.
Impression: The presence of a sinus rhythm with QRS widening, in which QRS morphology resembles RBBB conduction in the chest leads — but LBBB conduction with marked left axis deviation in the limb leads — is consistent with the entity known as “masquerading” bundle branch block (MBBB).
- MBBB is an uncommon clinical entity that identifies patients with severe underlying heart disease and a poor long-term prognosis.
- These patients are at high risk for developing complete AV block — and often require permanent pacing. The bradycardia and hypotensive episode described in the introduction of this case is not surprising.
Note: For more information about this case, visit https://tinyurl.com/KG-Blog-419.
The electrocardiogram (ECG) in the figure was recorded from an older man following a bradycardic and hypotensive episode. What ECG diagnosis is suggested by this tracing?
Subscribe Now for Access
You have reached your article limit for the month. We hope you found our articles both enjoyable and insightful. For information on new subscriptions, product trials, alternative billing arrangements or group and site discounts please call 800-688-2421. We look forward to having you as a long-term member of the Relias Media community.