![]() Secondary prevention, based on the treatment of associated atrial fibrillation risk factors, is emerging as a therapeutic option. In patients subjected to cardiac surgery or catheter ablation for the treatment of atrial fibrillation or showing atypical ECG patterns, macro-re-entrant and focal tachycardia mechanisms can be very complex and electrophysiological studies are necessary to guide ablation treatment in poorly tolerated cases. The term ‘flutter’ was coined to designate the visual and tactile rapid, regular atrial contraction induced by faradic stimulation in animal hearts, in contrast with irregular, vermiform contraction in atrial fibrillation (AF). 1,2 On the ECG, flutter was a regular continuous undulation between QRS complexes at a cycle length (CL) of ≤250 ms (≥240 bpm). Slower tachycardias displaying discrete P waves, separated by isoelectric baselines, were called ‘atrial tachycardia’. Early studies suggested that flutter had a re-entrant mechanism 3–5 but others attributed flutter to focal discharge. 6,7 Later human studies left the door open for a focal mechanism. 8 This was not a significant consideration when digitalis and very few antiarrhythmic drugs (AADs) were the only therapeutic armamentarium, but determining the mechanism involved in flutter has become crucial for the design and application of catheter and surgical ablation techniques. ![]() Modern electrophysiology (EP) has confirmed the re-entrant mechanism of typical flutter, and has opened wide the spectrum of mechanisms of macro-re-entrant tachycardias (MRTs), prompting a new, more open view of clinical ECG-based classification (see Figure 1A and 1B). Typical flutter is the type of MRT most frequently found in the clinical setting. ![]() The mechanism is a large re-entrant circuit contained in the right atrium (RA) with passive activation of the left atrium (LA). 10 Activation courses superoinferiorly in the anterior and lateral RA and inferosuperiorly in the septal RA, with a critical inferior turning point between the tricuspid ring and inferior vena cava (IVC) known as the cavotricuspid isthmus (CTI) (see Figure 2). ![]()
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