Unexpected Ventricular Standstill

Report:

Sinus rhythm 82/min

Borderline first degree AV block

Borderline left atrial abnormality (LAA)

Onset of complete AV block with no escape beats

Comment:

Some escape beats did appear, either through isoprenaline or spontaneously, and the degree of AV block lessened. It is interesting that the sinus rate slowed from 82 to 64 at the time of onset of the high-grade block, gradually to accelerate to 92 at the end of the strip. This suggest some reflex, possibly vagal, mechanism. This may well be related to the patient’s valve disease. Bradycardia and hypotension can occur unpredictably in aortic stenosis, causing syncope or sudden death38. The actual trigger remains unknown, but appears to involve left ventricular wall receptors.

This patient’s AV block is unexpected: in aortic stenosis one would see bradycardia leading to asystole, rather than a (relatively) preserved sinus mechanism blocked at the AV nodal level. She had the AV block unrelated to her hæmodynamics anyway, as the previous day’s ECG (Fig 59a) shows. The LAA is easily seen in most of the chest leads, with inter-peak distance of 1 mm; other evidence of LVH resides in RV6 > RV5.

Technically, the AV block in the original strip suggests Möbitz 2 mechanism since the PR intervals prior to ventricular standstill remain constant. This is unlikely in view of the narrow QRS and the fact that a vagal influence may be playing a role. Either Wenckebach or Möbitz 2, or, for that matter, a normal heart, can go into sudden asystole under appropriate circumstances.