In contrast to typical atrial flutter, incisional intra-atrial reentrant tachycardia (IART; Fig. 8.5a, b) is an increasingly more prevalent arrhythmia in the young cardiac patient following heart surgery. The vast majority of young patients presenting with IART have heart disease (about 84 %), most of them following surgery. The incidence of incisional IART is related to both the underlying congenital heart defect and the type of surgical repair. In general, the more complex the defect and the surgery (number of incisions and suture lines within the atria), the higher is the incidence. However with the development and widespread success of the arterial switch operation, replacing the atrial switch operation, the incidence of IART in patients with transposition has markedly decreased.

A unique and increasingly prevalent group of patients is those who underwent single ventricle palliations (Fontan sequence). The incidence of incisional IART appears to increase with age and to be directly related to the age at operation, the type of operation (most prevalent in the direct atriopulmonary connection), and the presence of sinus node dysfunction. Thus, a substantial number of Fontan patients (16–50 %) may develop incisional IART in their lifetime. Additionally, IART may be associated with an increased mortality, as one study of atrial flutter in the young; the congenital heart disease population had a mortality rate of 5 % in patients with medically controlled IART, and 20 % in medically uncontrolled patients.

In contrast to typical atrial flutter, incisional IART usually has a slower atrial rate—often less than 300 bpm (cycle length ≥200 ms). Atrial rates of 185–270 bpm (cycle length: 325–220 ms) are seen in Mustard patients and rates of 220–325 bpm (cycle length: 230–470 ms) in Fontan patients. The P-wave morphology is variable, often smaller and fractionated, and at times can be difficult to detect, particularly when evaluating on a few leads, typical with many event monitors. A multiple-lead ECG tracing is often necessary to detect the small P-waves, though a fixed ventricular rate of 100 to 150 bpm in patients following extensive atrial surgery or abnormality should suggest IART with 2:1 conduction to the ventricles. Furthermore, as the atrial rate slows, the possibility of 1:1 AV conduction increases, resulting in faster ventricular rates and an increased risk of hemodynamic compromise.

The primary difference between the typical form of atrial flutter and incisional IART is the nature of the barriers around which the reentry impulse circulates. In contrast to typical atrial flutter, incisional IART may involve not only the anatomically fixed structural barriers but also incisions, suture lines, patches, and baffles within the atria, as well as areas of fibrosis. The atria of patients with heart disease are also often subjected to increased pressure and volume loads, resulting in progressive fibrosis and changes in the electrophysiological properties. Clinical intracardiac electrophysiologic studies have confirmed the vulnerability of patients for IART after the Senning, Mustard, and Fontan procedures. This liability is likely due surgically created atrial discontinuities; focal atrial scarring and conduction block associated with suture lines; atrial fibrosis and thickening caused by pericardial inflammation and abnormal wall stress; abnormal atrial size and anatomy; increased atrial refractoriness associated with sinus node dysfunction; and prolonged duration of atrial activation. Many of these abnormalities may even be present before any of their operations. A number of experimental animal studies have reinforced the critical importance of the natural anatomical barriers in typical atrial flutter and found that surgical incisions and suture lines could facilitate IART, especially the crista terminalis, as well as potentially prevent inducibility of IART.

As incisional IART tends to be a progressive disease, most patients will require antiarrhythmic therapy at some point (Chap. 22) and anticoagulation will need to be considered. Unfortunately, this arrhythmia can be difficult to control, and, not uncommonly, as many as 2–3 antiarrhythmic drugs per patient may yield only suboptimal results. In patients who have infrequent episodes of IART or have had significant hemodynamic compromise due to rapid AV conduction, rate control should be considered in addition to anti-platelet or anticoagulation therapy. Beta-blocker and calcium channel blockers (diltiazem) are first-line agents. Beta-blockers may suppress sinus node function in an at-risk population, as well as possibly depressing ventricular function. Calcium channel blockers can exert a negative inotropic effect, but usually are well tolerated.

For patients with frequent or poorly tolerated episodes of IART, both rate and rhythm control is desirable. The mainstays of rhythm control agents include sodium channel blockers and potassium channel blockers as individual agents or in combination. In part, the antiarrhythmic mechanism of action of sodium channel blockers is to slow myocardial conduction velocity. While this can help in preventing reentrant atrial arrhythmias, it can also slow an IART, converting what once was a hemodynamically well-tolerated rapid atrial tachycardia with 2:1 AV conduction to a slower reentrant tachycardia with 1:1 AV conduction and a paradoxically faster ventricular rate. If a sodium channel blocker is used, consideration should be given to the addition of a rate control agent to protect against this adverse effect.

Potassium channel blockers, sotalol and amiodarone, and more recently dofetilide, which prolong the myocardial effective refractory period, are valuable agents in preventing IART. Sotalol and amiodarone also have the beneficial effect of slowing AV conduction. Nevertheless, the side effect profile of these mediations should be considered as dofetilide and sotalol have a higher risk of proarrhythmia while amiodarone has a greater risk of systemic adverse reactions (Chap. 22).

While the risk of thrombus formation is unknown, prophylactic anti-platelet or warfarin therapy is recommended for those with frequent or incessant IART, and aspirin should be considered in many patients with IART, even with only infrequent events. For patients with frequent and/or poorly tolerated episodes of IART anticoagulation therapy should also be considered for at least 3–6 months before considering weaning from the anticoagulation if arrhythmia suppression is obtained. In those with an acute episode of IART, the risk of thrombus formation increases with tachycardia duration. Therefore, cardioversion should be considered within the first 24 h if not anticoagulated. An echocardiogram, often transesophageal, is useful to exclude a preexisting thrombus before cardioversion. If one is seen, warfarin therapy should be instituted for at least 3 weeks prior to cardioversion if the clinical state permits.

Goals for electrophysiologic evaluation include: