3:2 Möbitz 2 AV Block

Report:

Sinus tachycardia 106/min

Left atrial abnormality (LAA)

Möbitz 2 second degree AV block, 3:2 conduction, with bigeminy

Indeterminate axis –140o

Right bundle branch block

Anteroseptal infarction, probably old

Comment:

In all instances of two consecutively conducted P waves the PR interval remains constant – defining the block as type 2 block. As expected, the intraventricular conduction is abnormal72, with RBBB and what probably was (or would be) a LAHB had the R waves not been reduced in the LV leads by the anterior infarction. The latter also accounts for QR morphology instead of RSR’ one in the anteroseptal leads: the primary R waves had been “amputated” by the infarct.

Almost certainly, this is an example of bilateral bundle branch block (BBBB); the AV block is mediated by 3:1 conduction through the remaining (left posterior) fascicle.

Here is a potentially life-threatening block, discovered on a routine admission ECG. The decision to pace the patient would be easy if he were not 85 years old, unable to walk and subject to other chronic and intercurrent illnesses. I passed the buck – reported the ECG and advised a repeat and a Cardiology consultation. The next day’s trace (Fig 110a) showed only 1:1 conduction. The patient collapsed in complete heart block three days later; temporary, then permanent pacing followed.