Home Magazines Editors-in-Chief FAQs Contact Us

ECG at the bedside: atrial fibrillation with randomly narrow and wide QRS complexes

MOJ Clinical & Medical Case Reports
Jochanan E Naschitz, Bait Balev Nesher


An electrocardiogram (ECG) displaying atrial fibrillation with randomly narrow and wide QRS complexes, the latter resembling left bundle branch block (LBBB), challenged the physicians’ diagnostic skills. First, Wolf Parkinson White syndrome and ventricular ectopy were excluded based on usual ECG criteria. Pertinent remaining possibilities were functional LBBB and Mahaim type preexcitation. Distinction between the two is made on intracardiac ECG by establishing the chronology of the His and QRS spikes: His spike preceding to QRS is consistent with functional LBBB while an inverted sequence is consistent with Mahaim type preexitation. In the present case invasive testing was judged to be unnecessary and hazardous. The patient was managed safely by slowing the ventricular rate with a beta-adrenergic blocker medication. Digitalis and calcium channel blockers were avoided, in considering their potential to accelerate the conduction through the accessory pathway


atrial fibrillation, pre-excitation, mahaim, left bundle branch block, ventricular tachycardia