![]() Although the atrial flutter rate will be slowed, more proportion of these atrial impulses will be conducted through AVN (enhanced conduction), by which net ventricular rate increases. In fact, class IC drugs have a vagolytic effect on AVN. The antiarrhythmic agents should be combined with AVN blockers to avoid the risk of rapid ventricular rates. In the absence of SHD, class IC agents are the first line medication. Several antiarrhythmic drugs have been somehow effective in AFL suppression, including class IC (flecainide and propafenone), and class III (usually sotalol and amiodarone) antiarrhythmics. However, medication may be tried in some situation (i.e. Hence, the ablation procedure with highly successful rate and low complication risk is the approach of choice for typical AFL. However, if there is a certain substrate for AFL recurrence such as enlarged RA or scar, medical suppression of AFL can be extremely difficult. If AFL occurs in the context of an acute disease process, long-term rhythm control medication is usually not required once the AFL is converted and the underlying pathologic process is eliminated. However, the rate control is difficult to achieve as opposed to AF. In order to control the rate, oral or intravenous atrioventricular node (AVN) blockers such as verapamil, diltiazem, beta blockers, and digoxin, can be used. Anticoagulation by using the same criteria as for AF, prior to cardioversion should be considered. Overdrive atrial pacing by a catheter in RA or in preexisting pacemaker/defibrillator is an effective alternative option in terminating typical AFL. Electrical cardioversion at a low energy of 50 J has very high success rate. Interestingly, intravenous ibutilide has been more effective than the formers up to 76% of patients. These class III antiarrhythmics prolong the refractory period leading slower cycle length which could terminate AFL. Antiarrhythmic medication such as intravenous amiodarone, sotalol, have been reported with a high success rate of chemical cardioversion. Cardioversion (electrical or chemical) is usually the initial treatment of choice. The clinical presentation will dictate acute therapeutic approach which may include cardioversion or rate control strategy. ![]() Also, the smooth vestibular portion around the tricuspid valve lies very close to the right coronary artery. This anatomic proximity explains the higher risk of AV block if ablation is done in the septal aspect. Of note, the septal part of the CTI is adjacent to the posterior extensions of the AV node as well as the middle cardiac vein. The pectinates, spare the myocardium just in atrial part of the tricuspid valve and makes the smooth portion of the CTI which is referred to as the vestibular portion. The subeustachian isthmus is the area between the tricuspid annulus and the eustachian ridge which ends in IVC junction. The central isthmus is concave and pouch-like in 47 and 45% of patients, respectively. The CTI is wider in the lateral portion and thinner in the central portion. The width and muscle thickness of CTI are variable, from several millimeters to around 3 cm in width and depth of 1 cm roughly. The CTI is bounded anteriorly by the tricuspid annulus and posteriorly by the ostium of the IVC and the eustachian ridge. ![]() However, the flutter wave morphology might change in the presence of underlying atrial disease, prior surgery, or previous ablation which makes the flutter wave morphology not a reliable indicator of AFL type. Clockwise AFL is observed in only 10% of clinical cases. It is also known as “common AFL” or “CTI-dependent AFL.” When the circuit rotates in the opposite direction, it is referred to as clockwise (CW) typical AFL or reverse typical AFL ( Figure 1). According to the new classification, typical AFL is a macroreentrant atrial tachycardia that usually proceeds up the atrial septum (counterclockwise or CCW), down the lateral atrial wall, and through the CTI between the tricuspid valve annulus and inferior vena cava (IVC). The most practical classification is based on isthmus versus non-isthmus dependency ( Diagram 1). ![]() In contrast, focal atrial tachycardia (AT) is a rapid abnormal atrial rhythm originating from a “point source” with a baseline between P waves on ECG. AFL is defined as abnormal atrial activity inside a reentrant circuit with a diameter more than 2 cm 2 at a high rate of 240–320 bpm which makes a continuous oscillation without an isoelectric baseline. ![]()
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