Atrial Flutter with High-Grade AV Block

Report:

Atrial flutter 260/min

Advanced (high-grade) AV block

Possible junctional escape beats

Nonspecific ST/T changes

Comment:

Complete block is excluded by the irregularity of the admittedly slow ventricular rate. Furthermore, one looks for the shortest cycles for conduction (capture beats are always early, quoth Marriott); the second and the fourth are identical, down to the position of F wave half-buried in the terminal portion of the QRS complex. The third and the seventh cycles are not the same length, but have the same F-R intervals (again, it helps to look at the F wave behind the QRS to time its predecessors, since it is etched on the repolarisation timeline.

The longest, fifth, cycle may well be terminated by a junctional escape beat, but there is no certainty there.

Below (Fig 56a) is a trace in fixed 4:1 block (some pedants would insist on calling it 4:1 conduction, strictly speaking more accurately). The conducted F waves are not those immediately in front of the ventricular complexes, but the ones preceding them – a common example of “skipping” or “over the top” conduction in flutter. The F-R interval in flutter is usually about 0.40”.