Concealed Non-Conduction

Report:

Atrial tachycardia 186/min

3:1 AV block

Comment:

Can one really tell? The descent of some T waves is sharper than expected or shallowly notched; the same cycles also have a notch immediately following the end of the preceding QRS complex. Something may be going on here, and at three times the QRS rate – hey presto!

The proof is obvious, on the next page. Unfortunately, I cannot say that I interpreted the original strip correctly before seeing the rest – I probably would not have and I cannot blame anyone else who does not. There were, however, enough staff in and around CCU who thought the tracings alternated between sinus rhythm with 1o AV block and atrial tachycardia, a view taken by the patient’s own GP who took the strips in his surgery. The palpitations he complained of were in fact in the neck – presumably atrial waves beating against a closed tricuspid valve!

The conduction ratio is odd (no pun intended!) and remained odd (5:1) in the 12-lead ECG below (Fig 116a). This implies an atypical arrangements of AV blocks, beyond the usual 2:1 + Wenckebach. On the page after next (Fig 116b), the block is variable, but the conduction ratios are still odd.

The atrial waves are quite similar to normal sinus P waves – the tachycardia is a high atrial or sino-atrial one. This patient had radiofrequency ablation for flutter the year before and was on amiodarone; he was now advised to stop the drug and represent himself for further EPS and ablation in four weeks’ time. No structural heart disease could be demonstrated.