![]() Lower loop reentry can rotate around the IVC in a counterclockwise (i.e., the impulse within the CTI travels from the septum to the lateral wall) or clockwise fashion. It often coexists with counterclockwise or clockwise typical AFL and involves posterior breakthrough across the crista terminalis. Lower loop reentry is a form of CTI-dependent AFL with a reentrant circuit around the inferior vena cava (IVC) therefore, it is confined to the lower part of the RA (see Fig. Microreentrant ATs, by definition, use a smaller circuit and in many regards behave more like other forms of focal ATs. Focal ATs are more frequently responsible for irregular ATs with frequent spontaneous interruption and reinitiation than are ATs observed with macroreentry. Typically, chronic or long-lasting atrial tachycardias (ATs) are macroreentrant. There is no single point of origin of activation, and atrial tissues outside the circuit are activated from various parts of the circuit.Ī description of MRAT mechanisms must be made in relation to atrial anatomy, including a detailed description of the obstacles or boundaries of the circuit and the critical isthmuses that may be targets for therapeutic action. Additionally, the obstacle can be fixed, functional, or a combination of both. The central obstacle can consist of normal or abnormal structures. The mechanism of MRAT is reentrant activation around a large central obstacle, generally several centimeters in diameter, at least in one of its dimensions. Atypical AFL is a term commonly used to describe all other macroreentrant atrial tachycardias (MRATs), regardless of the atrial cycle length (CL), but the former term introduces unnecessary confusion, and a mechanistic description of the tachycardia circuit is preferred. ![]() It is important to distinguish atypical flutter from typical flutter because this tells you something about how easy the rhythm will be to control (with meds) or treat (in EP lab).The term typical atrial flutter (AFL) is reserved for an atrial macroreentrant arrhythmia rotating clockwise or counterclockwise around the tricuspid annulus and using the cavotricuspid isthmus (CTI) as an essential part of the reentrant circuit. These can have all kinds of different A wave patterns and rates. For instance, there can be a circuit that relies on the tricuspid opening and a scar or one that relies on the mitral opening and an area previously treated with ablation for afib (endless possibilities). "Atypical flutter" is any other circuit in the heart that depolarization can travel along in a self-sustaining way. In clinical practice, the distinction of whether depolarization is clockwise or counterclockwise is not very relevant (does not affect management at all) so we usually don't mention it on ECGs, etc. The depolarization can be traveling either clockwise or counterclockwise in "typical flutter" (you can even have both, at different times, in the same patient). If someone has had surgery or ablation, the rules kind of go out the window.Īs others have said, "typical flutter" is anatomically defined: it is flutter that relies on the CTI as part of its circuit. The rate can be anywhere from 200 bpm (esp if there’s a significant degree of RA dilation) up to a little over 300 bpm. If it doesn’t look typical it is still probably typical. The ECG appearance is primarily due to the vector of activation along the lateral wall of the right atrium as seen on the inferior leads and in lead V1.įrom a practical standpoint: Patients without prior surgery or ablation, if it looks typical it very likely is typical. ![]() ![]() By this time the tissue is able to conduct and then you have a beat of atrial flutter. The enters the CTI from left to right, blocks, then travels around the tricuspid valve until it reaches the CTI from the other direction. This can be using zones of slow conduction from prior surgery, ablation, or areas of diseased atrial myocardium.Ĭounterclockwise (CCW) flutter is most common because there is a higher likelihood of PACs initiating the arrhythmia from the atria to the anatomical left of the CTI. The most accurate description of an atypical flutter is a macro reentrant atrial tachycardia. The nomenclature is really unfortunate, as flutter is a description of symptoms. As someone else said, the only difference is whether the arrhythmia circuit utilizes the cavotricuspid isthmus (CTI) in typical flutter, or something else in atypical flutter. ![]()
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