Right Atrial Anatomy and Flutter Circuits

In this episode, the CardioNerds (Dr. Naima Maqsood, Dr. Akiva Rosenzveig, and Dr. Colin Blumenthal) are joined by renowned educator in electrophysiology, Dr. Joshua Cooper, to discuss everything atrial flutter; from anatomy and pathophysiology to diagnosis and management. Dr. Cooper’s expert teaching comes through as Dr. Cooper vividly describes atrial anatomy to provide the foundational understanding to be able to understand why management of atrial flutter is unique from atrial fibrillation despite their every intertwined relationship. A foundational episode for learners to understand atrial flutter as well as numerous concepts in electrophysiology. Audio editing for this episode was performed by CardioNerds intern Dr. Bhavya Shah.  CardioNerds Atrial Fibrillation PageCardioNerds Episode PageCardioNerds AcademyCardionerds Healy Honor Roll CardioNerds Journal ClubSubscribe to The Heartbeat Newsletter!Check out CardioNerds SWAG!Become a CardioNerds Patron! Pearls "The biggest mistake is failure to diagnose”. Atrial flutter, especially with 2:1 conduction, is commonly missed in both inpatient and outpatient settings so look carefully at that 12-lead EKG so you can mitigate the stroke and tachycardia induced cardiomyopathy risk  Decremental conduction of the AV node makes it more challenging to rate control atrial flutter than atrial fibrillation  Catheter Ablation is the first line treatment for atrial flutter and is highly successful, but cardioversion can be utilized as well prior to pursuing ablation in some cases.  Class I AADs like propafenone and flecainide may stability the atrial flutter circuit by slowing conduction and thus may worsen the arrhythmia. Therefore, the preferred anti-arrhythmic medication in atrial flutter are class III agents.  Atrial flutter can be triggered by firing from the left side of the heart, so in patients with both atrial fibrillation and flutter, ablating atrial fibrillation makes atrial flutter less likely to recur.  BONUS PEARL: Dr. Cooper’s youtube video on atrial flutter is a MUST SEE!  Notes Notes: Notes drafted by Dr. Akiva Rosenzveig  What are the distinguishing features of atrial fibrillation and flutter?  Atrial flutter is an organized rhythm characterized by a wavefront that continuously travels around the same circuit leading to reproducible P-waves on surface EKG as well as a very mathematical and predictable relationship between atrial and ventricular activity  Atrial fibrillation is an ever changing, chaotic rhythm that consists of small local circuits that interplay off each other. Consequently, no two beats are the same and the relationship between the atrial activity and ventricular activity is unpredictable leading to an irregularly irregular rhythm  What are common atrial flutter circuits?  Cavo-tricuspid isthmus (CTI)-dependent atrial flutter is the most common type of flutter. It is characterized by a circuit that circumnavigates the tricuspid valve.  Typical atrial flutter is characterized by the circuit running in a counterclockwise pattern up the septum, from medial to lateral across the right atrial roof, down the lateral wall, and back towards the septum across the floor of the right atrium between the IVC and the inferior margin of the tricuspid valve i.e. the cavo-tricuspid isthmus. Surface EKG will show a gradual downslope in leads II, III, and AvF and a rapid rise at end of each flutter wave.   Atypical CTI-dependent flutter follows the same route but in the opposite direction (clockwise). Therefore, we will see positive flutter waves in the inferior leads   Mitral annular flutter is more commonly seen in atrial fibrillation patients who’ve been treated with ablation leading to scarring in the left atrium.  Roof-dependent flutter is characterized by a circuit that travels around left atrium circumnavigating a lesion (often from prior ablation), traveling through the left atrial roof, down the posterior wall, and around the pulmonary veins  Surgical/scar/incisional flutter is seen in people with a history of prior cardiac surgery and have iatrogenic scars in right atrium due to cannulation sites or incisions  How does atrial flutter pharmacologic management differ from other atrial arrhythmias?  The atrioventricular (AV) node is unique in that the faster it is stimulated, the longer the refractory period and the slower it conducts. This characteristic is called decremental conduction. In atrial fibrillation, the atrial rate is so fast that the AV node becomes overwhelmed and only lets some of those signals through to the ventricles creating an irregular tachycardia but at lower rates. In atrial flutter, the atrial rate is slower, therefore the AV node has more capability to conduct allowing for higher ventricular rates. Therefore, to achieve rate control one will need a higher dose of AV blocking medications. Atrial tachycardia may require even higher doses due to the increased ability of the AV node to conduct, as the atrial rates are slower than in atrial flutter.  Sodium channel blockers (Class I) such as flecainide and propafenone slow wavefront propagation, making it easier for the AV node to handle the atrial rates. This will end up leading to increased ventricular rates which can be dangerously fast. That is why AV nodal blockers should be used in conjunction with flecainide and propafenone.  What is the role of cardioversion in atrial flutter management?  Due to high success rate with atrial flutter ablation, ablation is the first line treatment. However, sometimes cardioversion may be utilized in patients depending on how symptomatic they are and how long it will take to get an ablation. Cardioversion may also be utilized preferentially when the atrial flutter was triggered by infection or cardiac surgery to see if it will come back.   If cardioversion is pursued, the patient will need to be anticoagulated due to the stroke risk after the procedure due to post-conversion stunning.  How effective is atrial flutter ablation?  The landmark Natale et al study in 2000 demonstrated 80% success rate after radiofrequency ablation as compared to 36% in patients on anti-arrhythmic therapy. The LADIP study in 2006 further corroborated these findings. Contemporary data shows above 90% success rate of atrial flutter ablation.  In patients who have had both atrial fibrillation and atrial flutter, most electrophysiologists would ablate both. However, in patients with atrial fibrillation, the atrial flutter usually is initiated by trigger spots firing in the left atrium. Once the atrial fibrillation is ablated, the flutter will become less likely. Therefore, there are those who say there’s no need to ablate the flutter circuit as well. Alternatively, if a patient has severe comorbidities and/or is high risk for ablation, one may consider performing the atrial flutter ablation only since atrial flutter is harder to manage medically compared with atrial fibrillation.   How do you manage atrial flutter in the acute inpatient setting?  In the inpatient setting, electrical cardioversion is often limited by blood pressure and the hypotensive effects of the sedatives required. If one is awake and too hypotensive, chemical cardioversion can be pursued. The most effective anti-arrhythmic for this is ibutilide. Amiodarone is not effective for acute cardioversion. Since ibutilide prolongs refractoriness in atrial and ventricular tissue, there’s a risk of long QT induced torsades de pointes. Pretreating with magneisum reduces the risk to 1-2%.  References Jolly WA, Ritchie WT. Auricular flutter and fibrillation. 1911. Ann Noninvasive Electrocardiol. 2003;8(1):92-96. doi:10.1046/j.1542-474x.2003.08114.x  McMichael J. History of atrial fibrillation 1628-1819 Harvey - de Senac - Laënnec. Br Heart J. 1982;48(3):193-197. doi:10.1136/hrt.48.3.193  Lee KW, Yang Y, Scheinman MM; University of Califoirnia-San Francisco, San Francisco, CA, USA. Atrial flutter: a review of its history, mechanisms, clinical features, and current therapy. Curr Probl Cardiol. 2005;30(3):121-167. doi:10.1016/j.cpcardiol.200  2023 ACC/AHA/ACCP/HRS Guideline for the Diagnosis and Management of Atrial Fibrillation: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2024;149(1):e167. doi:10.1161/  Cosío F. G. (2017). Atrial Flutter, Typical and Atypical: A Review. Arrhythmia & electrophysiology review, 6(2), 55–62. https://doi.org/10.15420/aer.2017.5.2  https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-11/Atrial-flutter-common-and-main-atypical-forms Natale A, Newby KH, Pisanó E, et al. Prospective randomized comparison of antiarrhythmic therapy versus first-line radiofrequency ablation in patients with atrial flutter. J Am Coll Cardiol. 2000;35(7):1898-1904. doi:10.1016/s0735-1097(00)00635-5  Da Costa A, Thévenin J, Roche F, et al. Results from the Loire-Ardèche-Drôme-Isère-Puy-de-Dôme (LADIP) trial on atrial flutter, a multicentric prospective randomized study comparing amiodarone and radiofrequency ablation after the first episode of symptomatic atrial flutter. Circulation. 2006;114(16):1676-1681. doi:10.1161/CIRCULATIONAHA.106.638395  https://www.acc.org/Membership/Sections-and-Councils/Fellows-in-Training-Section/Section-Updates/2015/12/15/16/58/Atrial-Fibrillation#:~:text=The%20first%20'modern%20day'%20account,in%20open%20chest%20animal%20models.&text=In%201775%2C%20William%20Withering%20first,(purple%20foxglove)%20in%20AFib.