Pacemaker Confusion in Pseudofusion: Transposition of Great Vessels

Report:

Sinus tachycardia 110/min 1

Left atrial abnormality (LAA) 1

Indeterminate abnormal axis ±194o 2

Right ventricular hypertrophy 3

Pacemaker sensing spikes (pseudofusion beats) 3

Comment:

The spikes occur after the onset of the QRS complex, producing so-called pseudofusion beats. They distort the QRS but do not contribute to it. Because the complexes are so large, the distortion by the pacemaker spikes is minimal. Some actually paced beats are shown below (Fig 20a). The paced beats are seen in escape-capture bigeminy with some of the escape (paced) beats being, possibly, true fusion beats –not with sinus beats, but junctional escape beats. The morphology of the paced beats suggests a left ventricular, possibly epicardial, electrode placement. The Cardiologist may have misreported the original ECG, but was right about the “pacer lead position”, even though on erroneous grounds!

The axis is what in pædiatric cardiology is usually reported as right axis. In adults, negative lead 2 denotes left axis, usually LAHB.

This is a fairly typical ECG of a patient with transposition of the great vessels. A thorough discussion of various ECG morphologies is provided by Schamroth16.

The patient died two days following a heart transplant in Sydney.