While evaluating an otherwise asymptomatic, healthy adolescent in clinic, you note an irregular rhythm on exam. Given this finding, you order an EKG (shown below). What do you think?


EKG Courtesy of Life in the Fast Lane: http://lifeinthefastlane.com/ecg-library

Diagnosis:  AV block: 2nd degree, Mobitz 1 (Wenckebach Phenomenon)


What is it?

  • Progressively lengthening of the PR interval and eventual “dropped QRS” complex, caused by increased refractory period of the AV node . The entire process tends to occur over 3-6 cardiac cycles (Doniger et al, 2006)
  • Following “dropped” beat, there is a diastolic pause, and cycle continues
  • Characteristically thought of as a “benign rhythm” found in asymptomatic individuals and there is low risk of progressing to third degree heart block. In fact, up to 10% of healthy will episodes of type 1, second degree heart block (Dickinson, 2005).
    • However, this may be seen in myocarditis, congenital heart disease, and following cardiac surgery

Created by:  Jason Mandell, MD

Reviewed by: Brian Lee, MD


Dickinson DF. “The Normal ECG in Childhood and Adolescence.” Heart. 2005;91:1626-1630

Doniger SJ et al. “Pediatric Dysrhythmias.” Pediatric Clinics of North America. 2006;53(1)85-105

Life in The Fast Lane: http://lifeinthefastlane.com/ecg-library/basics/wenckebach/