Elias Hanna, MD, Cardiology

Elias Hanna, MD, Cardiology

Bradyarrhythmias

1.Usually, symptoms are only seen when HR<40-50. If, however, a pt is in shock or florid HF, HR<60, or even 60-70, is inappropriate and is a contributor to the shock state.

2.Beside type of AV block, differentiate location of AV block.

Nodal location is generally benign: even if you progress to complete AV block, the escape is a “good” junctional escape.

Infra-nodal location is more dangerous: if it progresses to complete AV block, the escape is a slow ventricular rhythm.

-Mobitz 1 AV block is often nodal (PR prolongs then P drops; compare PR before and after the dropped P).

-Mobitz 2 AV block is always infra-nodal (one dropped P without preceding PR prolongation). Even if only one dropped P is seen on rhythm strip and even if rate is 60 bpm, if it is a regularly occurring P w/o progressive PR prolongationMobitz 2 ominous dx

-2:1 AV block could be Mobitz 1 or Mobitz 2 equivalent: if QRS is wide AV block is likely infranodal and the block is likely Mobitz 2

-Complete AV block can be nodal (characterized by a narrow junctional escape, 40-60 bpm), or infranodal (characterized by a wide ventricular escape≥120 ms, 20-40 bpm). Both cases, when symptomatic, are urgently treated with temporary PM followed by permanent PM, but infranodal AV block is a real emergency with an imminent risk of cardiac arrest regardless of symptoms.

-High-grade AV block is close to complete AV block. It means that most P waves are not conducted and there is an escape rhythm, but some P waves are conducted (you see a regular escape QRS rhythm interrupted by some irregularities)

Mobitz type 1 AV block

Mobitz type 2 AV block

2:1 AV block

3. Permanent pacemaker indications (after holding offending drugs):

-Mobitz 2 or 3rd degree AV block, even if asymptomatic

-Any symptomatic bradycardia<40-50 bpm (whether it is sinus bradycardia or slow rate associated with Mobitz 1 AV block or 2:1 AV block)

-Pauses >3 sec during wakefulness with symptoms

If in the latter 2 cases, if it is unclear whether symptoms are related to bradycardia or not, perform stress testing and see if there is chronotropic incompetence (inability to increase HR to 80% of the maximal age-predicted rate), or if AV block worsens with exercise as in infranodal block.

Permanent pacemaker is not indicated when brayarrhythmia or AV block are expected to resolve, e.g. inferior MI with transient complete AV block, AV block immediately after cardiac surgery, drug effect (B-blocker..), hyperkalemia. May need temporary pacemaker in those cases.

4.Temporary transvenous pacemaker is indicated in any complete, high-grade, or Mobitz 2 AV block that is symptomatic or infra-nodal complete AV block even if asymptomatic; or any bradycardia associated with shock. It is placed while awaiting permanent pacemaker placement (irreversible cause) or until a reversible cause resolves. Transcutaneous pacing and atropine may be used while inserting the transvenous pacer. Atropine is not effective for infranodal AV block