The atrioventricular (AV) node is a subendocardial structure located in the inferior-posterior right atrium. In an average adult, an AV node measures approximately 1 x 3 x 5 millimeters and sits within an anatomic region bordered posteriorly by the coronary sinus ostium, superiorly by the tendon of Todaro, and anteriorly by the septal tricuspid valve annulus. This anatomic region is also commonly referred to as the triangle of Koch. The blood supply to the AV node is from the AV nodal branch of the right coronary artery (90%) or the left circumflex artery (10%) depending on the right or left dominant blood supply to the heart. The first septal perforator of the left anterior descending artery also supplies blood to the AV node. 
Atrioventricular nodal reentrant tachycardia (AVNRT) is a type of paroxysmal supraventricular tachycardia that results due to the presence of a re-entry circuit within or adjacent to the AV node. Diagnosis of AVNRT requires visualization of an electrocardiogram (ECG). In most cases, an ECG will show heart rate between 140 and 280 beats per minute (bpm), and in the absence of aberrant conduction, a QRS complex of fewer than 120 milliseconds. ECG criteria based on the re-entrant circuits are as follows:
Atrioventricular nodal reentry tachycardia is usually not prevalent in patients with structural heart disease. The anatomy of the re-entrant circuit defines the type of AVNRT present. A Slow-Fast AVNRT accounts for 90% of AVNRTs with anterograde conduction by the slow AV nodal pathway and retrograde conduction by the fast AV nodal pathway. Fast-slow AVNRT represents approximately 5% to 10% of AVNRTs with anterograde conduction by the fast AV nodal pathway and retrograde conduction by the slow AV nodal pathway. Slow-slow AVNRTs account for 1% to 5% of AVNRTs with anterograde conduction by slow AV nodal pathways and retrograde conduction by slow atrial fibers.
Prevalence of atrioventricular nodal reentry tachycardia globally is similar to the United States. Close to 60% of the paroxysmal supraventricular tachycardia is AVNRT, with approximately two-thirds of that in women. A study found that the majority of patients presenting with symptoms due to AVNRT are in their twenties, but some patients might present with AVNRT in their seventh or eighth decade.
Despite being examined, it remains controversial whether fast and slow AV nodal conduction pathways share anatomical distinction or whether they represent functional diversity in the nodal structure.
Patients with atrioventricular nodal reentrant tachycardia usually present with symptoms of dizziness, syncope, shortness of breath, intermittent palpitations, pain/discomfort in the neck, pain/discomfort in the chest, anxiety, and polyuria secondary atrial natriuretic factor secreted mainly by the heart atria in response to atrial stretch. Patients with AVNRT and known history of coronary artery disease may present with a myocardial infarction secondary to the stress on the heart. Patients with AVNRT and known history of heart failure may present with acute exacerbation and possibly reduced ejection fraction secondary to tachycardia-induced cardiomyopathy.
Although syncope is an uncommon symptom in patients with AVNRT, it is typical in patients who have a heart rate above 170 bpm as less filling of the ventricles leads to the reduction in cardiac output and the decreased perfusion of the brain. Depression of the sinoatrial node secondary to tachycardia also may contribute to syncopal symptoms of patients who present with AVNRT. 
Patients with AVNRT usually present with a heart rate within the range of 140 to 280 bpm. If a patient has known heart failure or coronary artery disease, he may complain of chest pain and also may have symptoms of heart failure such as tachypnea with wheezes or swelling in the lower extremities on physical exam. During a physical exam, a provider might be able to appreciate Cannon A waves as the atrium contracts in conjunction with the ventricular contractions against a closed tricuspid valve. Hypotension secondary to decreased ventricular filling also may be a significant physical exam finding in patients presenting with AVNRT.
The most significant component of the assessment for a patient who presents with signs and symptoms of atrioventricular nodal reentrant tachycardia is a history and physical exam. These should include vital signs (respiratory rate, blood pressure, temperature, and heart rate) and an electrocardiogram. A patient presenting with AVNRT should undergo evaluation for any unknown underlying coronary artery disease or heart failure. During an assessment, it should be established whether the patient is hemodynamically stable based mainly on his blood pressure, mental status, and respiratory rate. Initial evaluation of patients with AVNRT can include testing to access the patient's thyroid and pulmonary function, together with routine blood work and echocardiography.
Management of patients presenting with atrioventricular nodal reentry tachycardia begins with an initial evaluation of their hemodynamically stability. Hemodynamically unstable patients present with tachycardia associated with hypotension, ischemic chest pain, altered mental status, respiratory failure, or shock. These patients need their AVNRT terminated electrically with an urgent electrical cardioversion. Hemodynamically stable patients should be treated first with vagal maneuvers to cease the rhythm acutely. If attempted twice and the patient remains in AVNRT, modified vagal exercises should be performed at least twice to terminate the arrhythmia. Once such maneuvers are unsuccessful or are inappropriate, intravenous (IV) medical therapy is warranted.
First-line medical therapy is IV adenosine which can be administered up to 18 mg given in increments of 6 mg in the absence of contraindications such as severe bronchospastic lung disease or severe coronary artery disease. In the event both vagal maneuvers and IV adenosine are unsuccessful or ruled inappropriate, IV non-dihydropyridine calcium channel blockers, IV beta-blockers or IV digoxin are next in consideration. Selection of these IV medical agents is based upon the presence of concomitant factors, such as in patients with AVNRT and hypotension; IV digoxin may be appropriate as it lacks anti-hypertensive properties. Subsequently, in a patient who is actively wheezing secondary to a reactive airway, IV non-dihydropyridine calcium channel blockers should be used first.
IV adenosine terminates approximately 80% of AVNRT arrhythmias. Patients in whom medical treatment and Valsalva maneuvers fail or those who cannot tolerate medication due to its side effects might opt for catheter ablation as a one-time definitive cure. Catheter ablations in patients with AVNRT have a high success rate which is reported to be as high as 95%. Chronic medical therapy with Class III or IC antiarrhythmics such as flecainide, propafenone, amiodarone, dofetilide or sotalol can be done in instances where the patient does not respond to calcium channel blockers or beta-blockers and refuses catheter ablation. Selection of these antiarrhythmics usually is based on patients comorbidities and its side effect profiles.
Once a narrow QRS complex tachycardia is present on an electrocardiogram, and the rhythm is evaluated as regular, differential rhythms include the following:
Prognosis is generally good when the rhythm is promptly identified by a healthcare provider.
If not identified promptly symptomatic complications such as syncope, fatigue or dizziness can occur.
Educating patients at risk for this rhythm and making a closed loop communication between them and their providers can help further improve the management of these rhythms.
In rare instances, atrioventricular nodal reentry tachycardia can result in sudden cardiac arrest.
If available patient education should be provided using resources familiar to the patient including online resources and pamphlets.
|||Koch's triangle sized up: anatomical landmarks in perspective of catheter ablation procedures., Inoue S,Becker AE,, Pacing and clinical electrophysiology : PACE, 1998 Aug [PubMed PMID: 9725153]|
|||Clinical importance of Koch's triangle size in children: a study using 3-dimensional electroanatomical mapping., Sumitomo N,Tateno S,Nakamura Y,Ushinohama H,Taniguchi K,Ichikawa R,Fukuhara J,Abe O,Miyashita M,Kanamaru H,Ayusawa M,Harada K,Mugishima H,, Circulation journal : official journal of the Japanese Circulation Society, 2007 Dec [PubMed PMID: 18037746]|
|||Koch's triangle and the atrioventricular node in Ebstein's anomaly: implications for catheter ablation., Sánchez-Quintana D,Picazo-Angelín B,Cabrera A,Murillo M,Cabrera JA,, Revista espanola de cardiologia, 2010 Jun [PubMed PMID: 20515623]|
|||Arterial blood supply of the atrioventricular node and main bundle., Van der Hauwaert LG,Stroobandt R,Verhaeghe L,, British heart journal, 1972 Oct [PubMed PMID: 5086972]|
|||Anatomical aspects of the arterial blood supply to the sinoatrial and atrioventricular nodes of the human heart., Pejković B,Krajnc I,Anderhuber F,Kosutić D,, The Journal of international medical research, 2008 Jul-Aug [PubMed PMID: 18652764]|
|||A simple model of the right atrium of the human heart with the sinoatrial and atrioventricular nodes included., Podziemski P,Zebrowski JJ,, Journal of clinical monitoring and computing, 2013 Aug [PubMed PMID: 23430363]|
|||Arterial supply to sinuatrial and atrioventricular nodes: imaging with multidetector CT., Saremi F,Abolhoda A,Ashikyan O,Milliken JC,Narula J,Gurudevan SV,Kaushal K,Raney A,, Radiology, 2008 Jan [PubMed PMID: 18024438]|
|||Arrhythmias Involving the Atrioventricular Junction., Di Biase L,Gianni C,Bagliani G,Padeletti L,, Cardiac electrophysiology clinics, 2017 Sep [PubMed PMID: 28838549]|
|||Atrioventricular Reentrant Tachycardia., Marzlin KM,Webner C,, AACN advanced critical care, 2017 Summer [PubMed PMID: 28592483]|
|||Atrioventricular Nodal Reentrant Tachycardia., Marzlin KM,, AACN advanced critical care, 2017 Spring [PubMed PMID: 28254859]|
|||Anatomical and electrophysiological variations of Koch's triangle and the impact on the slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia: a study using 3D mapping., Yamaguchi T,Tsuchiya T,Nagamoto Y,Miyamoto K,Sadamatsu K,Tanioka Y,Kadokami T,Murotani K,Takahashi N,, Journal of interventional cardiac electrophysiology : an international journal of arrhythmias and pacing, 2013 Jun [PubMed PMID: 23408048]|
|||Gender-related differences in patients with atrioventricular nodal reentry tachycardia., Liuba I,Jönsson A,Säfström K,Walfridsson H,, The American journal of cardiology, 2006 Feb 1 [PubMed PMID: 16442401]|
|||Physiologic evidence for a dual A-V transmission system., MOE GK,PRESTON JB,BURLINGTON H,, Circulation research, 1956 Jul [PubMed PMID: 13330177]|
|||Neurohumoral and hemodynamic mechanisms of diuresis during atrioventricular nodal reentrant tachycardia., Abe H,Nagatomo T,Kobayashi H,Miura Y,Araki M,Kuroiwa A,Nakashima Y,, Pacing and clinical electrophysiology : PACE, 1997 Nov [PubMed PMID: 9392809]|
|||Supraventricular tachycardia., Ganz LI,Friedman PL,, The New England journal of medicine, 1995 Jan 19 [PubMed PMID: 7800009]|
|||Syncope associated with supraventricular tachycardia. An expression of tachycardia rate or vasomotor response?, Leitch JW,Klein GJ,Yee R,Leather RA,Kim YH,, Circulation, 1992 Mar [PubMed PMID: 1537103]|
|||Comparison of the ages of tachycardia onset in patients with atrioventricular nodal reentrant tachycardia and accessory pathway-mediated tachycardia., Goyal R,Zivin A,Souza J,Shaikh SA,Harvey M,Bogun F,Daoud E,Man KC,Strickberger SA,Morady F,, American heart journal, 1996 Oct [PubMed PMID: 8831363]|
|||Frequency of disabling symptoms in supraventricular tachycardia., Wood KA,Drew BJ,Scheinman MM,, The American journal of cardiology, 1997 Jan 15 [PubMed PMID: 9193013]|
|||Studies on hemodynamic instability in paroxysmal supraventricular tachycardia: noninvasive evaluations by head-up tilt testing and power spectrum analysis on electrocardiographic RR variation., Doi A,Miyamoto K,Uno K,Nakata T,Tsuchihashi K,Shimamoto K,, Pacing and clinical electrophysiology : PACE, 2000 Nov [PubMed PMID: 11138299]|
|||Contemporary management of paroxysmal supraventricular tachycardia., Ferguson JD,DiMarco JP,, Circulation, 2003 Mar 4 [PubMed PMID: 12615783]|
|||Valsalva maneuver for termination of supraventricular tachycardia., Pandya A,Lang E,, Annals of emergency medicine, 2015 Jan [PubMed PMID: 23932719]|
|||Efficacy and safety of out-of-hospital self-administered single-dose oral drug treatment in the management of infrequent, well-tolerated paroxysmal supraventricular tachycardia., Alboni P,Tomasi C,Menozzi C,Bottoni N,Paparella N,Fucà G,Brignole M,Cappato R,, Journal of the American College of Cardiology, 2001 Feb [PubMed PMID: 11216977]|
|||Electrophysiologic effects of adenosine in patients with supraventricular tachycardia., Glatter KA,Cheng J,Dorostkar P,Modin G,Talwar S,Al-Nimri M,Lee RJ,Saxon LA,Lesh MD,Scheinman MM,, Circulation, 1999 Mar 2 [PubMed PMID: 10051297]|
|||Adenosine and the treatment of supraventricular tachycardia., Rankin AC,Brooks R,Ruskin JN,McGovern BA,, The American journal of medicine, 1992 Jun [PubMed PMID: 1605147]|
|||2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society., Page RL,Joglar JA,Caldwell MA,Calkins H,Conti JB,Deal BJ,Estes NA 3rd,Field ME,Goldberger ZD,Hammill SC,Indik JH,Lindsay BD,Olshansky B,Russo AM,Shen WK,Tracy CM,Al-Khatib SM,, Circulation, 2016 Apr 5 [PubMed PMID: 26399663]|
|||Intravenous adenosine in the emergency department management of paroxysmal supraventricular tachycardia., Cairns CB,Niemann JT,, Annals of emergency medicine, 1991 Jul [PubMed PMID: 2064090]|
|||Episodic drug treatment in the management of paroxysmal arrhythmias., Margolis B,DeSilva RA,Lown B,, The American journal of cardiology, 1980 Mar [PubMed PMID: 7355758]|
|||Acute conversion of paroxysmal supraventricular tachycardia with intravenous diltiazem. IV Diltiazem Study Group., Dougherty AH,Jackman WM,Naccarelli GV,Friday KJ,Dias VC,, The American journal of cardiology, 1992 Sep 1 [PubMed PMID: 1510006]|
|||Adenosine: electrophysiologic effects and therapeutic use for terminating paroxysmal supraventricular tachycardia., DiMarco JP,Sellers TD,Berne RM,West GA,Belardinelli L,, Circulation, 1983 Dec [PubMed PMID: 6640877]|
|||Intravenous verapamil for termination of re-entrant supraventricular tachycardias: intracardiac studies correlated with plasma verapamil concentrations., Sung RJ,Elser B,McAllister RG Jr,, Annals of internal medicine, 1980 Nov [PubMed PMID: 7212475]|
|||Determinants of immediate success for catheter ablation of atrioventricular nodal reentry tachycardia in patients without junctional rhythm., Bagherzadeh A,Keshavarzi T,Farahani MM,Goodarzynejad H,, Journal of interventional cardiac electrophysiology : an international journal of arrhythmias and pacing, 2014 Jan [PubMed PMID: 24101150]|
|||Catheter Ablation of Atypical Atrioventricular Nodal Reentrant Tachycardia., Katritsis DG,Marine JE,Contreras FM,Fujii A,Latchamsetty R,Siontis KC,Katritsis GD,Zografos T,John RM,Epstein LM,Michaud GF,Anter E,Sepahpour A,Rowland E,Buxton AE,Calkins H,Morady F,Stevenson WG,Josephson ME,, Circulation, 2016 Nov 22 [PubMed PMID: 27754882]|
|||Current management and clinical outcomes for catheter ablation of atrioventricular nodal re-entrant tachycardia., Chrispin J,Misra S,Marine JE,Rickard J,Barth A,Kolandaivelu A,Ashikaga H,Tandri H,Spragg DD,Crosson J,Berger RD,Tomaselli G,Calkins H,Sinha SK,, Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology, 2018 Apr 1 [PubMed PMID: 28541507]|
|||Meta-analysis of ablation of atrial flutter and supraventricular tachycardia., Spector P,Reynolds MR,Calkins H,Sondhi M,Xu Y,Martin A,Williams CJ,Sledge I,, The American journal of cardiology, 2009 Sep 1 [PubMed PMID: 19699343]|
|||Patients with supraventricular tachycardia presenting with aborted sudden death: incidence, mechanism and long-term follow-up., Wang YS,Scheinman MM,Chien WW,Cohen TJ,Lesh MD,Griffin JC,, Journal of the American College of Cardiology, 1991 Dec [PubMed PMID: 1960318]|