Report:

Supraventricular tachycardia 165/min 1

Electrical alternans 2

Termination of paroxysm 0

Atrial escape beat (fusion) 2

Pacemaker escape beat 1

Sinus beat (fusion) 2

VEB (last complex) 1

Nonspecific ST/T changes, possible LVH (R2 = 15 mm) 1

Comment:

During the SVT there is some atrial activity at the S/ST junction, probably retrograde P waves, but no definite pattern of conduction can be established. It made me think, however, how it would have been tempting to place a magnet over the pacemaker and try to interrupt the SVT by underdrive pacing. I have not done it myself since 1975, but remember how delightful it felt.

The electrical alternans at this (fast) rate has no clinical significance; neither do the repolarisation changes6.

The pacing spike appears rather late after the termination of the SVT, projecting a rate of only 60/min, probably due to the programmed rate hysteresis. It may also have been triggered by the small preceding atrial wave, since this is an atrial-sensing pacemaker. Whether it triggered the pacemaker or not, the atrial escape certainly contributed a good deal to the ensuing QRS complex, which is a fusion beat between it and the pacemaker. The following beat, preceded by a sinus P wave, is also a fusion beat, this time with more contribution from the pacemaker. In the subsequent 12-lead ECG shown below (Fig 5a), all the paced beats are like the second paced beat in the original recording – they are all triggered and contributed to by sinus P waves and relatively narrow at 0.12 sec. As expected, the axis of these partially paced beats is now deviated to the left in the frontal plane. A “pure” paced beat from the apex of the right ventricle would look like LBBB with LAD in the frontal leads, like in Fig 4.

Fig 5a.

Fig 6. 58 year old man with permanent pacemaker since aortic valve replacement (AVR) five years previously.