Tuesday, February 24, 2015

When is permanent pacing indicated for AV block?

I'm working through MKSAP 16's section on cardiovascular disease. As much as I hate to be immodest, it's a content area I think I know just a little something about, particularly in the area of electrophysiology. I was drawn to their statement on permanent pacing after acute MI (AMI). Sprinkled throughout MKSAP are sets of high value care recommendations for various specialties, apparently their own version of Choosing Wisely.

The pacing recommendation, which is to wait several days after the occurrence of AV block (AVB) before inserting a permanent pacemaker (PPM) in order to see if the block persisted, struck me as awfully simplistic. Pacing recommendations for AVB have strong underpinnings in physiology which have withstood evidence based scrutiny. The relevant electrophysiology, far more often than not, can be assessed at the bedside via simple electrocardiography. Well, maybe I should qualify that by saying it's true provided adequate skill in interpretation of the ECG is brought to the bedside.

Things have changed through the years. Clinical skills in this area have deteriorated, in part because AVB complicating AMI is much less common in today's reperfusion era than it once was. The question of what to do with AVB after AMI seldom comes up anymore. Before the reperfusion era it was routine. The guiding principle back then was that, at least in acute anterior MI, when the block was subjunctional, that is true type II block, permanent pacing was indicated no matter how transient the block. (Caveat: the atypical situation of block arising in the common bundle of His is a nuanced topic, beyond the scope of this post).

So what about the current guidelines? The STEMI guidelines refer this topic to the device therapy guidelines which say in part:

1. Permanent ventricular pacing is indicated for persistent second-degree AV block in the His-Purkinje system with alternating bundle-branch block or third-degree AV block within or below the His Purkinje system after ST-segment elevation MI. (Level of Evidence: B) (79,126 –129,131)

2. Permanent ventricular pacing is indicated for transient advanced second- or third-degree infranodal AV block and associated bundle-branch block. If the site of block is uncertain, an electrophysiological study may be necessary. (Level of Evidence: B) (126,127) 

For patients in general with acquired AVB the guidelines include the following, listed under the class IIa category:

4. Permanent pacemaker implantation is reasonable for asymptomatic type II second-degree AV block with a narrow QRS.

When type II second-degree AV block occurs with a wide QRS, including isolated right bundle-branch block, pacing becomes a Class I recommendation. (See Section 2.1.3, “Chronic Bifascicular Block.”) (Level of Evidence: B) (70,76,80,85)

The recommendation summary is much more extensive but this small sample illustrates the complexity of decision making and the reliance on assessment of the anatomic site of block via electrocardiography (bedside electrophysiology). When it comes to pacing decisions post MI there's considerably more to it than the MKSAP recommendations would indicate.


james gaulte said...

How often have you found the "right answer" one that seems to be the "choosing wisely" answer?

R. W. Donnell said...

Though some of the choosing wisely recommendations may be helpful I've become increasingly sceptical. It's a mixed bag. Many of the recs seem to have been thrown out there with little thought just because the professional society leaders were asked to. Others are based on the faulty assumption that a lack of published evidence warrants a "hard stop." The basic idea of high value care is fine but the campaign as it has been promulgated fails critical appraisal (to borrow a phrase coined by the EBM founders).