Accelerated idioventricular rhythm

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Overview
The rate of cardiac contraction is determined by the intrinsic rate of depolarisation of the cardiac cells. In normal hearts the sinoatrial node in the atria depolarises at a rate of 70 beats per minute. This suppresses the intrinsic depolarisation of the other parts of the heart.

The accelerated idioventricular rhythm occurs when depolarisation rate of a normally suppressed focus increases to above that of the "higher order" focuses (the sinoatrial node and the atrioventricular node). This most commonly occurs in the setting of a sinus bradycardia.

Accelerated Idioventricular Rhythms are ectopic ventricular rhythms at rates between 40 bpm and 100 to 120 bpm. The ventricular origin of this rhythm can be demonstrated by the usual EKG criteria which include AV dissociation, fusion, and capture complexes.

The incidence of Accelerated Idioventricular Rhythms following acute MI is reported to be between 8 and 36%. This rhythm can also be seen in patients with primary myocardial disease, hypertensive, rheumatic, and congenital heart disease. Digoxin may cause of accelerated idioventricular rhythm.

EKG characteristics

 * Regular rhythm at a rate of 40 to 100-120 BPM.
 * QRS complexes are abnormal and wide.
 * The ventricular complexes are usually but not necessarily dissociated from the P waves.
 * Ventricular capture and fusion beats are common.

Differential Diagnosis

 * 1) Because of its slower rate it may resemble NSR. Look for numerous fusion beats. The term accelerated isorhythmic ventricular rhythm has been suggested.
 * 2) Must be distinguished from junctional tachycardia with preexisting IVCDs. But in these patients there are no fusion or capture beats.

Clinical Correlation

 * 1) Seen in both AMIs and IMIs.
 * 2) Commonly seen following reperfusion.
 * 3) Usually occurs during sinus bradycardia.
 * 4) May also be caused by digitalis.

AIVR appears similar to ventricular tachycardia but is benign and doesn't need any treatment.

Additional resources

 * ECGpedia: Course for interpretation of ECG
 * The whole ECG - A basic ECG primer
 * 12-lead ECG library
 * Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG
 * ECG information from Children's Hospital Heart Center, Seattle
 * National Heart, Lung, and Blood Institute, Diseases and Conditions Index
 * A history of electrocardiography
 * EKG Interpretations in infants and children