Facing acute arrhythmias in CHD patients needs an early interplay between emergency physician and cardiologists.

Hemodynamically poorly tolerated tachycardia or ventricular fibrillation resulting in pulseless arrest requires management according to AHA/ACC/ESC guidelines for Adult Cardiac Life Support (ACLS) [8]. When direct current cardioversion is required, paddles or patches have to be positioned taking into account cardiac location in the chest [6].

In tolerated arrhythmias, 12-lead electrocardiogram (ECG) of the event should be registered. Knowledge of anatomical defect and collection of surgical reports are also fundamental for best acute and long-term management and should be obtained as soon as possible.

Hemodynamically tolerated tachycardia should be managed according to well-established adult guidelines, while taking into consideration CHD-specific issues [6] on drug therapy: antiarrhythmic drugs (AAD) are frequently poorly tolerated due to negative inotropic and other side effects, and few data exist on their safety and efficacy [6].

For atrial arrhythmias the thromboembolic risk must be assessed before cardioversion, reminding that in moderate and severe complexity CHD, it is high even when onset is <48 h [6].

Unexplained syncope in adults with CHD is an alarming event that may have several potential etiologies, including conduction abnormalities and bradyarrhythmias, atrial and/or ventricular arrhythmias, and nonarrhythmic causes [6].

In patients with CHD, the majority of sudden cardiac deaths (SCD) have an arrhythmic etiology, but up to 20 % may be nonarrhythmic, as in cerebral or pulmonary embolism, myocardial infarction, heart failure, and aortic or aneurysmal rupture [5]. SCD is responsible for approximately one-fifth of the mortality in adult’s CHD, with a greater risk observed in certain malformations (tetralogy of Fallot, Ebstein’s disease, left-sided obstructive disease). However, the annual mortality rates are low compared with adult population (0.1–0.3 % per patient-year) [1].

Atrial tachyarrhythmias (ATs), the most frequent in CHD, have been identified as a risk factor for SCD. The mechanism has been attributed to rapid AV conduction, most notably at times of exertion, with hemodynamic instability caused by the atrial tachyarrhythmia itself or by its degeneration into a secondary ventricular tachyarrhythmia [7].

Prevalence of ATs is 3 times higher than what is observed in general population, and it is reported that 20-year-old patients with CHD have an equivalent risk of a 55-year-old women without CHD: patients with CHD are young with aged hearts [9]; atrial fibrillation (AF) is less common than atrial flutter accounting for 20–30 % of all ATs [10, 11].

The most common mechanism of tachycardia seen in the adult CHD patient population is macro-reentry within the atrial muscle. It is defined as intra-atrial reentrant tachycardia (IART) [7].

This arrhythmia usually is a late postoperative disorder, and it may arise after nearly all procedures involving a right atriotomy (even simple closure of an atrial septal defect); the incidence is clearly highest after the Mustard–Senning and Fontan operations, in which 30–50 % can be expected to develop a symptomatic episode during follow-up. Generally, IART tends to be slower than typical flutter, with atrial rates in the range of 170–250 beats per minute. In the setting of a healthy AV node, these rates will frequently allow a pattern of 1:1 AV conduction that may result in hemodynamic instability, syncope, or possibly death [3, 7]. Rate control should be achieved as soon as possible. Beta-blocking drugs and nondihydropyridine calcium channel antagonists can be used to achieve ventricular rate control with insufficient evidence to recommend one agent over another; since beta-blockers are associated with a decreased incidence of ventricular tachyarrhythmias in many conditions, it may be reasonable to liberalize their use in this patient population if well tolerated [6].

Sustained IART or AF lasting ≥48 h is an established risk for thromboembolism [12, 13], but moderate and complex forms of CHD have a predisposition to thromboembolic complications estimated to be10- to100-fold higher than in age-matched controls: in these patients it may be prudent to rule out intracardiac thrombus prior to cardioversion regardless of the duration of IART or AF [6].

Once atrial arrhythmia is recognized and thromboembolic risk ruled out, acute interruption can be performed with electrical cardioversion, overdrive pacing (in patients with implanted atrial or dual chamber pacemaker/defibrillators), or antiarrhythmic drugs.

Reciprocating tachycardia and some non-automatic focal atrial tachycardias may be terminated by vagal maneuvers, intravenous adenosine, or non-dihydropyridine calcium channel antagonists, with the exception of patients with an anterograde conducting accessory pathway (WPW).

There is a paucity of literature regarding pharmacologic conversion of IART or AF in adults with CHD; ibutilide has been tested in a small pediatric series [14], but there are no efficacy and safety data regarding acute conversion of IART or atrial fibrillation with class IA and IC and other class III drugs in patients with CHD [6]: electrical cardioversion should therefore be preferred. Anterior–posterior pad positioning may be needed in the setting of marked atrial dilation [5].

Experience with chronic pharmacologic therapy for IART in adults with CHD has been discouraging [6, 10, 11, 15], resulting in a growing preference for non-pharmacologic options in most centers.

Nevertheless, in those with moderate or complex forms of CHD, a rhythm control treatment strategy (i.e., maintenance of sinus rhythm) is generally preferred to rate control as the initial management approach [6].

Ventricular arrhythmias. There are several scenarios in which high-grade ventricular arrhythmias may develop in CHD. The most familiar involves macro-reentrant VT as a late complication in postoperative patients who have undergone ventriculotomy and/or patching such as tetralogy of Fallot repair which is the best studied. Reentry circuit is caused by conduction corridors around regions of scar in the RV outflow tract (RVOT). The incidence of late VT or SCD for repaired tetralogy has been estimated between 0.5 and 6.0 % in various series [3, 7]. Some patients with slow organized VT may be hemodynamically stable at presentation, but VT tends to be rapid for the majority, producing syncope or cardiac arrest as the presenting symptom. Serious ventricular arrhythmias may also develop in a number of other malformations, even in the absence of direct surgical scarring to ventricular muscle when the right ventricle supports the systemic circulation or in the presence of a failing systemic ventricle. The appearance of ventricular arrhythmias in these cases commonly coincides with deterioration in hemodynamic status [7].