Congratulations to Itamar for the best answer and discussion with kudos to Dr. Ben Kaufman as well for the first answer!
This is atrial fibrillation with Wolff-Parkinson-White Syndrome (WPW). Itamar gave a very good discussion of wide-complex tachycardias. In our patient, the differential is indeed narrowed down by the irregularly irregular rhythm, in conjunction with a short PR and polymorphic QRS complexes gives us the answer. The giveaway is the change in QRS morphology from beat to beat secondary to the variable contributions of the AV nodal and accessory pathway to ventricular depolarization.
WPW is defined by pre-excitation causing runs of tachyarrhythmia. Pre-excitation is the activation of the ventricles by the atria yet bypassing the AV node via an accessory pathway. In WPW, this pathway is called the Bundle of Kent. Usually, the Bundle of Kent will conduct both from the atria to the ventricles (anterograde/orthodromic if tachyarrhythmia) and from the ventricles back up to the atria (retrograde/antidromic if tachyarrhythmia). Anterograde-only conduction is rarely seen, and retrograde-only conduction is seen approximately 15% of the time.
Atrial flutter and atrial fibrillation are seen in approximately 7% and 20% respectively of patients with WPW. Rapid impulses from the atria have not only the AV node but also the accessory pathway to access the ventricles, putting those with WPW at a higher risk of paroxysmal afib/flutter with rapid ventricular rate. Correctly stated above, any AV nodal-blocking agents such as beta-blockers or calcium channel-blockers will emphasize the accessory pathway only and increase the risk of the rhythm degenerating into ventricular tachycardia and ventricular fibrillation.
Treatment – avoid AV nodal-blocking agents, if stable procainamide or DC cardioversion, if unstable DC cardioversion. Electrophysiologic study and ablation is the only potentially curative treatment.
Supervised by Dr. Jennifer Martindale.
Michaud GF, Stevenson WG. Supraventricular Tachyarrhythmias. In: Kasper D, Fauci A, Hauser S, Longo D, Jameson J, Loscalzo J. eds. Harrison’s Principles of Internal Medicine, 19e. New York, NY: McGraw-Hill; 2015.
Life In the Fast Lane, Pre-Excitation Syndromes. http://lifeinthefastlane.com/ecg-library/pre-excitation-syndromes/
eabram
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