Electrocardiogram shows underlying atrial fibrillation with ventricular pacing and premature ventricular complexes. As shown here, in some cases the electronic spikes at the beginning of the QRS may be of sufficiently low amplitude as to escape detection, leading to a mistaken diagnosis of a bundle branch block (eg, left bundle branch block morphology with right ventricular pacing).
Reproduced with permission from: Nathanson LA, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians. http://ecg.bidmc.harvard.edu.
