First Degree and Second Degree Mobitz Type I (or Wenckebach)
Heart Block in Your Child
Sinus rhythm: The heart works like an electrical pump. The sinoatrial (SA) or sinus node
is the heart’s natural pacemaker. It controls the heart rate. The sinus node sends an
electrical signal to the top chambers of the heart called the atria. This causes them to
contract. The atrioventricular (AV) node is like an electrical conduction cable that sends
the signal to the lower chambers of the heart called ventricles. This causes them to
First Degree Heart Block
First degree heart block is a delay in sending the electrical signal between the SA node
and the ventricles. First degree AV block can be normal if it happens at rest or during
sleep. The time it takes to send the signal from the SA node to the ventricles should
shorten during exercise or with increased heart rates. With first degree AV block every
atrial beat sends an electrical signal to the ventricles. Your cardiology provider may
suggest more tests and clinic visits.
Second Degree Mobitz Type I (or Wenckebach)
Wenckebach is a gradual delay in sending the electrical signal from the SA node to the
ventricles with each beat until there is a single dropped beat. This type of heart block may
be normal during rest or sleep, but is not normally seen at increased heart rates or during
exercise. Your cardiology provider may suggest more tests and clinic visits.
Signs and Symptoms
Most infants and children have no signs or symptoms of first degree AV block or
A member of the health care team does a complete exam and a health history.
An electrocardiogram (ECG or EKG) is done to look at the heart’s electrical activity.
Normal numbers for the heart’s electrical conduction system depend on your child’s age.
Electrical conduction in the heart gradually slows with age.
A Holter monitor is a 24 or 48 hour recording done to help evaluate the heart’s
Who Do I Call With Questions?
Your child’s doctor, nurse, or clinic staff can answer any questions. Our phone number is
(608) 263-6420. Please ask for Pediatric Cardiology.
AFCH Pediatric Cardiology Website: www.uwhealth/kidshearts.
Your health care team may have given you this information as part of your care. If so, please use it and
call if you have any questions. If this information was not given to you as part of your care, please check
with your doctor. This is not medical advice. This is not to be used for diagnosis or treatment of any
medical condition. Because each person’s health needs are different, you should talk with your doctor
or others on your health care team when using this information. If you have an emergency, please call
911. Copyright © 5/2017 University of Wisconsin Hospitals and Clinics Authority. All rights reserved.
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