Editing Third-degree atrioventricular block (section)

{{Infobox medical condition (new)
| name            = Third-degree atrioventricular block
| synonyms        = Complete heart block
| image           = CompleteHeartBlock.jpg
| caption         = 12-lead ECG showing complete heart block
| pronounce       =
| field           = [[Cardiology]]
| symptoms        = [[Dizziness]], [[Syncope (medicine)|Fainting]], [[Breathlessness|Shortness of breath]], [[Sudden cardiac death]]
| complications   =
| onset           =
| duration        =
| types           =
| causes          = Fibrosis in [[cardiac conduction system]], [[myocardial infarction]], post-cardiac surgery, medication, [[vagal tone]], electrolyte disturbances
| risks           =
| diagnosis       = [[Electrocardiography|Electrocardiogram]]
| differential    =
| prevention      =
| treatment       = [[Electronic pacemaker|Pacemaker]]
| medication      =
| prognosis       =
| frequency       =
| deaths          =
|alt=}}

'''Third-degree atrioventricular block''' (AV block) is a medical condition in which the electrical impulse generated in the [[sinoatrial node]] (SA node) in the [[atrium (heart)|atrium]] of the [[heart]] can not propagate to the [[ventricle (heart)|ventricles]].<ref name="urlLesson VI - ECG Conduction Abnormalities">{{cite web |url=http://ecg.utah.edu/lesson/6#Complete |title=ECG Conduction Abnormalities |access-date=2009-01-07}}</ref>

Because the impulse is blocked, an accessory pacemaker in the lower chambers will typically activate the ventricles.  This is known as an ''[[escape rhythm]]''. Since this accessory pacemaker also activates independently of the impulse generated at the SA node, two independent rhythms can be noted on the [[electrocardiogram]] (ECG).
* The [[P wave (electrocardiography)|P waves]] with a regular P-to-P interval (in other words, a [[sinus rhythm]]) represent the first rhythm.
* The [[QRS complex]]es with a regular R-to-R interval represent the second rhythm. The [[PR interval]] will be variable, as the hallmark of complete heart block is the lack of any apparent relationship between P waves and QRS complexes.