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COSÍO, F.G., et al.: Atypical Flutter: A Review. Understanding of typical flutter circuits led the way to the study of other forms of macroreentrant tachycardias of the atria, and to their treatment by catheter ablation. It has become evident that the ECG classification of atrial flutter and atrial tachycardia by a rate cutoff and the presence or absence of isoelectric baselines between atrial deflections is not a valid indicator of tachycardia mechanism. Macroreentrant circuits where activation rotates around large obstacles are the most common arrhythmias found in patients with atypical forms of flutter or atrial tachycardia, especially after surgery for congenital heart disease, however, focal mechanisms can also be found. Large areas of low voltage electrograms, suggestive of severe myocardial damage (fibrosis or infiltration) can be found in many atypical macroreentrant tachycardias at the center of the circuit. Many of these circuits can be mapped precisely, critical isthmuses can be defined, and effective catheter ablation can be performed. The need to match activation maps with anatomy precisely, makes computer assisted, anatomically precise mapping a useful tool. Entrainment techniques have to be used sparingly to avoid tachycardia interruption. In complex cases, ablation can be done in sinus rhythm, after definition of conducting channels between low voltage areas and scars or anatomic obstacles. Long-term prognosis is uncertain and depends on the underlying pathology. (PACE 2003; 26:2157–2169) [ABSTRACT FROM AUTHOR]

A case of severe mitral regurgitation with refractory heart failure, after atrioventricular junction ablation and pacemaker implant, was solved with left ventricular pacing. Mitral regurgitation was related to a change in segmental left ventricular motion during right ventricular pacing. [ABSTRACT FROM AUTHOR]

Atrial flutter (AF) mapping has shown circular activation in the right atrium (RA), with a ''counterclockwise" rotation in a frontal view. The myocardial isthmus between the inferior vena cava and the tricuspid valve (IVC-T) closes the activation circuit in its caudal end. The reproducibility of this activation pattern, and the fact that some "rare" AF with a "clockwise" rotation of activation use the same circuit, suggests that reentry is greatly facilitated by the anatomical arrangement of the caudal end of the RA. This suggested that ablation of the IVC-T isthmus may interrupt AF and prevent its recurrence. We have applied radiofrequency (RF) current to the IVC-T isthmus in nine patients, producing sudden interruption of activation at this point in five (all those treated with large surface electrode catheters). In three others, RF produced acceleration or disorganization, leading to interruption. Preliminary follow-up data suggest a favorable effect on AF recurrence, either by preventing it, or by making antiarrhythmic drugs effective. [ABSTRACT FROM AUTHOR]

We have studied the electrophysiological correlates of atrial repetitive responses, induced by single extrastimuli, in a group of 25 patients undergoing electrophysiologic studies for a variety of supraventricular and ventricular arrhythmias. The incidence of repetitive responses was not related to a previous history of atrial tachyarrhythmias. Repetitive responses were observed only when the extrastimulus elicited a significant intra-atrial conduction delay, as measured from the extrastimulus artifact, to two or three points in the atria. This condition was fulfilled only when the basic atrial rhythm was paced, and it was also facilitated by increasing atrial rate, which shortened the atrial effective refractory period. Atrial pacing thus seemed to facilitate the production of atrial repetitive responses by both promoting intra-atrial conduction delays during extrastimulation, and by shortening the atrial refractory period. Atrial repetitive responses are probably a nonspecific phenomenon, unrelated to a tendency towards atrial tachyarrhythmias; their mechanism is probably local re-entry, related to slow conduction of impulses during incomplete repolarization, and under favorable conditions they may precipitate atrial flutter or fibrillation in predisposed patients. [ABSTRACT FROM AUTHOR]

Typical ECG of that described for Brugada syndrome was elicited in a patient diagnosed with labyrinthopathy during Infusion of dimenhydrinate, a first-generation antihistamine usually used to treat motion sickness. Although the patient had no history of syncope or palpitations, and there was no family history of cardiac disease or sudden death, the ECG abnormality was reproduced later with intravenous flecainide, and an asymptomatic Brugada syndrome was diagnosed. [ABSTRACT FROM AUTHOR]