Common flutter in a patient with congenital heart disease

ECG: Bradycardia (45 beats/minute) with typical common flutter pattern; repetition of regular, all identical F waves; sawtooth pattern in inferior leads (fast ascending line, peaked summit, slower descending line, with no return to isoelectric line); poorly visible and low voltage F waves in lead I, positive in V1 and negative in V6; the duration of the atrial cycle is 210 ms (rate approximately 290 beats/minute); variable atrioventricular conduction (1:8, 1:6, 1:5); in this patient, atrioventricular conduction appears to be altered, explaining the ratio between the number of F waves and the number of QRS complexes; right bundle branch block with wide QRS (175 ms), right axis, delayed intrinsicoid deflection in V1, V2; probable right ventricular hypertrophy;

Comments: The surgical repair of a tetralogy of Fallot has less detrimental effects on the atrial mass than a Senning, Mustard or Fontan type intervention. However, there is a high prevalence of atrial rhythm disorders observed on the long term after the surgery. Typically, outside the early postoperative phase, an event-free interval of 10 to 15 years without occurrence of atrial arrhythmia is observed. The prevalence then increases to 20% in adulthood. Even though the surgery of this disease is not focused on the atrium, numerous factors favor the occurrence of atrial arrhythmias. Indeed, the association between atriotomy, right atrial scar, cannulation of the atrium and prolonged volume and/or pressure overload 1) leads to the development of a widespread atrial electrophysiological remodeling with stretching of the atrial mass, (anisotropy of the fibers) and (2) favors the formation of slow conduction atrial isthmuses conducive to macro-reentry.

Two types of organized right atrial arrhythmia are described: the cavo-tricuspid isthmus-dependent flutter and the scar-related atrial flutter. Focal arrhythmias are extremely rare. As in this patient, the so-called common isthmus-dependent flutters are the most frequent. A reentry macro circuit can also follow a right lateral atriotomy with the occurrence of a scar-related atrial flutter. The duration of the atrial reentry cycle is generally shorter in a scar-related atrial flutter than in an isthmus-dependent flutter, the circuit being shorter. The ablation of a scar-related atrial flutter consists in establishing a block line between two anatomical obstacles: generally, between the lower part of the scar and the inferior vena cava, more rarely between the scar and the tricuspid valve or between the upper part of the scar and the superior vena cava.

Take-home message: Patients with congenital heart disease who have undergone surgery with right lateral atriotomy preferentially present 2 types of organized atrial arrhythmias: common isthmus-dependent flutter and scar-related atrial flutter. The duration of the atrial reentry cycle is generally shorter (faster atrial rate) for a scar-related atrial flutter than for an isthmus-dependent flutter, the circuit being shorter.