Isorhythmic A-V dissociation

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Vendhan Ramanujam M.B.B.S [2]

Synonyms and keywords: Isorhythmic AV dissociation


An atrioventricular dissociation characterized by independent and equally beating atrial and ventricular pacemakers, in the absence of a retrograde conduction from the ventricular depolarization to the atria is called as isorhythmic AV dissociation. Isorhythmic dissociation is not common in the general population and it is the most innocent type of AV dissociation.


Isorhythmic AV dissociation is a AV dissociation initiated by slowing of SA node due to sinus arrhythmia, sinus bradycardia, sinus arrest, or sinoatrial block. This allows an independent ventricular pacemaker response like either junctional rhythm (giving a normal or near normal QRS appearance and duration) or idioventricular rhythm (with a more bizarre, wide QRS) to take over the ventricles. In the presence of some degree of antegrade and retrograde atrioventricular block, there is a synchronization of independently beating sinus or atrial pacemaker with the junctional or ventricular pacemaker such that each discharges in the absolute refractory period of the other.

  • Both the independent atrial and ventricular rates are bradycardic and nearly identical, in contrast to other types of AV dissociation. When they both are bradycardic and synchronized, captures will not occur and a complete AV dissociation will ensue.
  • Both fusion beats and capture beats may be present when either the atrial or ventricular rate becomes faster than the other with antegrade or retrograde conduction.
  • Both P waves and the QRS complexes look related with the P wave moving closer to and then farther away from the QRS, maintaining an illusion of a normal atrioventricular conduction sequence. Occasionally, the P wave might move into and get buried within the QRS complex, only to move back out again in front of the QRS in the subsequent beats. The two pacemakers will remain independent as long as the SA node rate is bradycardic.
  • When this rhythm occurs intermittently with normal sinus rhythm, it is called accrochage.
  • When the isorhythmic dissociation is persistent, it is called as synchronization. Synchronization has two distinct patterns like, the pattern which is characterized by a rhythmic fluctuation of the interval between the P and QRS waves, most often the P wave oscillating gradually back and forth across the QRS; that is, with periodically varying of P-R and R-P intervals. In the second pattern, the P-R or R-P interval do not undergo rhythmic fluctuations, but the P and R waves are in a relatively fixed position with respect to each other.[1]


Life Threatening Causes

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

Common Causes

Causes by Organ System

Cardiovascular Acute coronary syndrome, acute rheumatic fever, amyloidosis, Andersen cardiodysrhythmic periodic paralysis, Brugada syndrome, cardiac lymphoma, cardiac transplantation, cardioinhibitory syncope, complete heart block, congenital heart disease, congestive heart failure, coronary reperfusion therapy, dilated cardiomyopathy, hypertensive heart disease, hypertrophic cardiomyopathy, ischemic heart disease, Jervell and Lange-Nielsen syndrome, Lev's disease, long QT syndrome, myocardial bridging, myocardial contusion, myocardial infarction, myocardial rupture, myocarditis, NSTEMI, pericarditis, Romano-Ward syndrome, sick sinus syndrome, sinoatrial block, sinus arrest, sinus bradycardia, sinus node fibrosis, STEMI, tachycardia-bradycardia syndrome, Timothy syndrome, valvular heart disease
Chemical/Poisoning Berberine, carbamate poisoning, grayanotoxin, organophosphate poisoning, parathion poisoning, poisonous spider bites, pyrethroid poisoning, scorpion toxin
Dental No underlying causes
Dermatologic No underlying causes
Drug Side Effect Acetylcholine, all-trans retinoic acid, amiodarone, anthracyclines, antiarrhythmic drugs, barbiturate, beta-blockers, bupivacaine, calcium channel blockers, carbamazepine, cholinesterase inhibitors, cimetidine, citalopram, clonidine, daunorubicin, digoxin, diltiazem, diphenhydramine, donepezil, doxorubicin, edrophonium, epirubicin, granisetron, guanethidine, halothane, idarubicin, isoprenaline, lithium, mepivacaine, mesalamine, methyldopa, methylprednisolone, nelfinavir, neostigmine, nicorandil, phenothiazine, phenytoin, procainamide, propafenone, propanolol, propofol, pyridostigmine, quinidine, remifentanil, reserpine, ropivacaine, tacrine, thiamylal, timolol, tramadol, tricyclic antidepressants, urapidil, verapamil
Ear Nose Throat No underlying causes
Endocrine Diabetic ketoacidosis, Hashimoto's thyroiditis, hyperthyroidism, hypothyroidism, pheochromocytoma
Environmental Hypothermia
Gastroenterologic Amyloidosis
Genetic Brugada syndrome, Emery-Dreifuss muscular dystrophy, Jervell and Lange-Nielsen syndrome, Kearns-Sayre syndrome, limb-girdle muscular dystrophy type 1B (LGMD1B), long QT syndrome, muscular dystrophy, myotonic dystrophy, Romano-Ward syndrome, Timothy syndrome
Hematologic No underlying causes
Iatrogenic Cardiac catheterization, cardiac resynchronization therapy, cardiac transplantation, coronary artery bypass grafting, Fontan procedure, heart surgery, post lung transplantation
Infectious Disease Acute rheumatic fever, Chagas disease, diptheria, Lyme disease, septic shock
Musculoskeletal/Orthopedic Muscular dystrophy, myotonic dystrophy, Timothy syndrome
Neurologic Severe brain injury
Nutritional/Metabolic Diabetic ketoacidosis, hyperkalemia, hypermagnesemia, hypocalcemia, metabolic acidosis
Obstetric/Gynecologic No underlying causes
Oncologic Cardiac lymphoma
Ophthalmologic No underlying causes
Overdose/Toxicity No underlying causes
Psychiatric Severe anorexia nervosa, Takotsubo cardiomyopathy
Pulmonary Hypoxia
Renal/Electrolyte Acute renal failure, amyloidosis
Rheumatology/Immunology/Allergy Neonatal lupus erythematosus, scleroderma, Sjogren's syndrome
Sexual No underlying causes
Trauma Myocardial contusion
Urologic No underlying causes
Miscellaneous Idiopathic

Causes in Alphabetical Order


  1. Levy MN, Edflstein J (1970). "The mechanism of synchronization in isorhythmic A-V dissociation. II. Clinical studies". Circulation. 42 (4): 689–99. PMID 11993309. Unknown parameter |month= ignored (help)

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