Cardiovascular Critical Care I

diagnoses to the source of conduction problems (see Table 6).

Narrow QRS complexes commonly indicate AV nodal dysfunction.

Wide QRS complexes may indicate dysfunction in either the AV node or the His-Purkinje system.

Disease 2011:xiv; BMJ 2002;324:662-5; BMJ 2002;324:415-8)

Type

ECG Example

Description

First degree

Delayed conduction from the sinoatrial

(SA) node to the atrioventricular (AV)

node characterized by a P-R interval

> 0.2 s (1 big box on the ECG strip)

Relatively benign; however, underlying

contributors should be evaluated and

minimized (i.e., β-blockers and other AV

nodal blocking agents)

Second-degree

Mobitz type 1

(Wenckebach)

Consistent P-P interval with progressive

prolongation of the P-R (indicating

impaired SA to AV node conduction)

eventually resulting in absence of a QRS

complex because of the lack of AV node

conduction of atrial impulse

Of most concern in older adult patients

in whom this may be indicative of

progressive conduction disease; may be

more benign in younger patients

“Longer, longer, longer, drop … must be

Wenckebach”

Second degree

Mobitz type 2

Consistent P-P interval and consistent

P-R interval duration with spontaneous

absence of a QRS complex because of

the lack of AV node conduction of atrial

impulse

Usually indicative of more significant

conduction disease and associated with

syncope, HF, and increased mortality rates

Third degree

(Complete heart

block)

Characterized by consistent P-P intervals,

consistent R-R intervals, and variable/

random P-R interval representing

independent, uncoordinated atrial and

ventricular conduction (A-V dissociation).

The arrows on this ECG strip identify P

waves, showing regular P-P interval with

varying P-R interval