Sharpen Your Calipers - Dr. Littmann

Bifascicular Block and Second Degree AV Block

1.     In asymptomatic individuals, chronic bifascicular block does not usually require cardiac work-up; the prognosis is generally benign

2.     The following high-risk features, however, warrant urgent evaluation:
           a.   Bifascicular block and syncope
           b.   Bifascicular block and intermittent second degree AV block
           c.   1:1 AV conduction at slower sinus rates but higher grade block (i.e., 2:1 AV conduction) at faster 
                  sinus rates (“acceleration-dependent AV block”)

3.     Evaluation and management of patients with bifascicular block:
          a.   Actively search for nonconducted P waves in the 12-lead ECG
          b.   Always review telemetry strips and actively search for episodes of second degree AV block      
                 (blocked P waves)
          c.   In symptomatic patients with bifascicular block who develop acceleration-dependent second 
                 degree AV block and a very slow ventricular rate, carotid massage or IV beta blocker can 
                 paradoxically restore 1:1 AV conduction
          d.   Patients with bifascicular block and syncope require admission and cardiology consultation for 
                 possible pacemaker implantation
          e.   Patients with bifascicular block and intermittent second degree AV block require cardiology 
                 consultation for possible pacemaker implantation

The Pacemaker ECG

1.     Ventricular pacing: always try to determine what the atria are doing

2.     Sinus P wave in front of each paced QRS complex indicates dual chamber (A-V sequential) pacemaker where the ventricular pacer is tracking sinus rhythm

3.     Two pacer spikes about 5 mm apart indicate AV sequential pacing

4.     If there are no P waves or 2 pacer spikes, search for the presence of retrograde P waves after the paced QRS complexes; retrograde P waves are sharp negative in the inferior leads (in II, III and aVF) and usually upright in V1

5.     If there are no P waves in front of the paced QRS complexes and no retrograde P waves present, always consider the possibility of underlying atrial fibrillation