Correspondence

Cardiac Pacing

N Engl J Med 1996; 334:1476-1477May 30, 1996

Article

To the Editor:

According to the World Health Organization and the American College of Cardiology, type II second-degree atrioventricular block is defined as a single nonconducted P wave associated with constant PR intervals before and after the blocked impulse, provided there are at least two consecutive conducted P waves to indicate the behavior of the PR intervals,1 and the sinus rate remains constant.2

In their review of cardiac pacing, Kusumoto and Goldschlager (Jan. 11 issue)3 perpetuate some errors in the 1991 American College of Cardiology–American Heart Association guidelines for pacemaker implantation.4 Their definition of type II block, as in the guidelines, lends itself to misinterpretation, because the constancy of the PR interval after a blocked impulse is not emphasized.1 The authors also indicate that with 2:1 atrioventricular block, the distinction between type I and type II cannot be made with certainty. It would be preferable to state that with 2:1 atrioventricular block, the distinction between type I and type II does not apply, because only one conducted P wave is available before the blocked one. Thus, 2:1 atrioventricular block should not be classified as either type I or type II.1,5

Kusumoto and Goldschlager state, “An asymptomatic patient with a second-degree type I atrioventricular block should not receive a permanent pacemaker.” In chronic bundle-branch block and type I second-degree atrioventricular block, the site of second-degree atrioventricular block lies in the His–Purkinje system in about 30 percent of cases.6 The prognosis seems similar for type I and type II infranodal second-degree atrioventricular block, and many cardiologists recommend pacing in patients with asymptomatic type I infranodal block, as do the American College of Cardiology–American Heart Association guidelines (a class II indication).4 Kusumoto and Goldschlager believe that in asymptomatic 2:1 atrioventricular block, bundle-branch block indicates infranodal 2:1 atrioventricular block and is thus a class II indication. Yet 2:1 atrioventricular block can be an atrioventricular nodal block in at least 30 percent of cases,6 with a better prognosis,6 and is not necessarily a class II indication.

In the section on acquired atrioventricular block, the authors state that asymptomatic type II second-degree atrioventricular block constitutes a class II indication. Yet in the section on fascicular block, they state that asymptomatic bifascicular and trifascicular block with type II second-degree atrioventricular block constitutes a class I indication. Such recommendations come directly from the 1991 guidelines.4 These disparate recommendations for the same condition are illogical, because type II atrioventricular block is associated with disease of the bundle branches in at least 70 percent of cases.6

S. Serge Barold, M.D.
Genesee Hospital, Rochester, NY 14607-4055

6 References

1. 1

   Barold SS. ACC/AHA guidelines for implantation of cardiac pacemakers: how accurate are the definitions of atrioventricular and intraventricular conduction blocks? Pacing Clin Electrophysiol 1993;16:1221-1226
   CrossRef | Web of Science | Medline

2. 2

   Rardon DP, Miles WM, Mitrani RD, Klein LS, Zipes DP. Atrioventricular block and dissociation. In: Zipes DP, Jalife J, eds. Cardiac electrophysiology: from cells to bedside. 2nd ed. Philadelphia: W.B. Saunders, 1995:935-42.
   

3. 3

   Kusumoto FM, Goldschlager N. Cardiac pacing. N Engl J Med 1996;334:89-98
   Full Text | Web of Science | Medline

4. 4

   Dreifus LS, Fisch C, Griffin JC, Gillette PC, Mason JW, Parsonnet V. Guidelines for implantation of cardiac pacemakers and antiarrhythmia devices: a report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures (Committee on Pacemaker Implantation). J Am Coll Cardiol 1991;18:1-13
   CrossRef | Web of Science | Medline

5. 5

   Zipes DP, Gettes LS, Akhtar M, et al. Guidelines for clinical intracardiac electrophysiologic studies: a report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures (Subcommittee to Assess Clinical Intracardiac Electrophysiologic Studies). J Am Coll Cardiol 1989;14:1827-1842
   CrossRef | Web of Science | Medline

6. 6

   Denes P. Atrioventricular and intraventricular block. Circulation 1987;75:Suppl III:III-19
   

Author/Editor Response

The authors reply:

To the Editor: We thank Dr. Barold for his comments on our review of cardiac pacing. We are also familiar with some of the imprecise definitions and concepts of certain forms of atrioventricular block, as provided in the 1991 American College of Cardiology–American Heart Association guidelines for the implantation of cardiac pacemakers.1 It is also true that 2:1 atrioventricular conduction of sinus impulses can in fact often be accurately ascribed to type I or type II atrioventricular conduction on the basis of additional information about how, and under what circumstances, the atrioventricular-conduction ratio can be altered. For example, 2:1 atrioventricular conduction, with a block occurring at the atrioventricular node, is generally associated with narrow, normal-appearing QRS complexes and long PR intervals of the conducted beats. Vagolytic maneuvers, which enhance atrioventricular conduction, alter the atrioventricular-conduction ratio — for instance, from 2:1 to 4:3 — allowing the diagnosis of type I atrioventricular block to be made. In a similar fashion, 2:1 atrioventricular conduction in which the block is infranodal is often associated with bundle-branch block and normal PR intervals of the conducted complexes. The behavior of the PR intervals and conduction ratio in response to certain maneuvers (such as the administration of atropine) usually clarifies the issue. In our article, we state that with 2:1 atrioventricular conduction, the distinction between type I and type II atrioventricular block cannot often be made with certainty, although certain clues to the correct diagnosis can be most helpful.

Dr. Barold correctly points out the role of intraventricular conduction system disease in the consideration of pacing therapy in patients with atrioventricular block and correctly warns that the site of conduction block cannot always be predicted from the surface electrocardiogram, whatever the number or the nature of the clues. It seems, however, that Dr. Barold's main argument concerns the American College of Cardiology–American Heart Association guidelines1 and not our statements. We respect his argument and even agree with it, in part. It was our intention, however, not to provide arguments against the guidelines but to summarize the recommendations as they currently stand in print. Updating and revising all guidelines is obviously appropriate and necessary, and is an ongoing process undertaken by the American College of Cardiology–American Heart Association Task Force.

Fred Kusumoto, M.D.
Lovelace Medical Center, Albuquerque, NM 87108

Nora Goldschlager, M.D
University of California, San Francisco, San Francisco, CA 94110

1 References

1. 1

   Dreifus LS, Fisch C, Griffin JC, Gillette PC, Mason JW, Parsonnet V. Guidelines for implantation of cardiac pacemakers and antiarrhythmia devices: a report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures (Committee on Pacemaker Implantation). J Am Coll Cardiol 1991;18:1-13
   CrossRef | Web of Science | Medline

Citing Articles (1)

Citing Articles

1. 1

   ARJANG RUHPARWAR, AXEL HAVERICH. (2003) Prospects for Biological Cardiac Pacemaker Systems. Pacing and Clinical Electrophysiology 26:11, 2069-2071
   CrossRef