Despite not being severe, this condition can be quite symptomatic. Although the differential diagnosis from similar entities is outlined, the guidelines state that diagnosis is based on the exclusion of these other entities. This statement might be controversial because this tachycardia has its own signs, as noted by the authors.

The incorporation of ivabradine as the therapeutic axis is notable because this drug was not included in the previous guidelines. In recent years, valuable evidence has emerged in favor of ivabradine, either as monotherapy or in combination with BBs, a fact incorporated into the 2015 American guidelines. These data have resulted in a IIa recommendation.

The poor outcomes of catheter ablation mean that it is no longer recommended, not even with the IIb indication assigned in the previous guidelines.

The data on the drug therapy of this infrequent arrhythmia are limited to acute suppression of inducibility in 2 patients with verapamil and in 4 with amiodarone. Accordingly, it is not surprising that this approach is only assigned a IIb indication. Because there are more data with good outcomes for catheter ablation, this strategy is assigned a IIa indication; all of the recommendations have level of evidence C. The previous guidelines did not assign formal indications for this arrhythmia.

The most novel information on the management of this syndrome refers to the success of regulated exercise programs. This is reflected in the document, which, unlike the previous guidelines, assigns these programs a IIa A indication. All other measures, including pharmacological ones, have become IIb indications due to their low effectiveness and adverse effects.

There are few data on the acute management of this arrhythmia. Although numerous studies have been published, most included SVTs of diverse origins and only a minority or an unknown proportion were focal atrial tachycardias. Therefore, very general recommendations are made, with class IIa or IIb indications for almost all antiarrhythmic drugs, similar to previous guidelines. The document fails to emphasize electrocardiographic documentation of the response to vagal maneuvers and adenosine administration, which may provide a key to the diagnosis.

A similar situation is seen with chronic drug therapy. Generic conclusions are reached and a IIa recommendation is assigned to almost all antiarrhythmic drugs; the recommendation for amiodarone is IIb based on 2 pediatric series with 3 and 7 patients.

Catheter ablation, with a proven 75% to 100% efficacy in multiple studies, is an established recommendation (class I) in patients with recurrent tachycardia. The latest Spanish Catheter Ablation Registry reported an 86% success rate in Spain.4

More attention is dedicated to this arrhythmia than in previous guidelines and specific recommendations are made. Nonetheless, the poor effectiveness of rhythm control drugs is recognized; they are considered effective if they control heart rate. Under this prism, IIa recommendations are assigned to both calcium antagonists and selective BBs, and the document recognizes that, if they fail, atrioventricular node ablation also has a IIa indication. The next step is pacemaker implantation.

The guidelines continue to consider atrial fibrillation separately from flutter, artificially so. This division does not correspond to reality, given the similarity of the resulting conditions (risk factors), signs of myocardial remodeling,7 and the tendency of flutter to progress to fibrillation, either spontaneously8 or after ablation.

The electrocardiographic pattern of typical counterclockwise flutter raises questions. As in previous guidelines, predominantly negative waves in inferior leads and positive waves in V1 are described, whereas a previous consensus document considered that the deflection in V1 can be biphasic or negative.9 Flutter ECG must always be assessed within the clinical context. It is important to recognize the limitations of ECG to reveal the underlying circuit in the presence of antiarrhythmic drugs, previous surgery affecting the atria, or extensive ablations. Specifically, an atypical ECG may be associated with cavotricuspid isthmus-dependent circuits, easily manageable with ablation.

The guidelines highlight the effectiveness of electrical cardioversion of flutter. Further evidence has been obtained from mid- and long-term follow-up data showing a lower incidence of recurrence than in atrial fibrillation, supporting the proposal of the new guidelines to not always indicate ablation for a first flutter episode.10,11 It is important to note the contraindication to the use of class Ic drugs for the treatment of these re-entries.

Attention is drawn to the uncertain threshold for embolic risk used to establish chronic anticoagulation in flutter not related to fibrillation, given its possibly lower embolic risk.2 Because the established recommendations for anticoagulation in patients with flutter mirror those of fibrillation, the authors note that it is not possible to make a clear recommendation in this regard; however, a CHA2DS2-VASc score ≥ 4 has recently been proposed.12

Atrioventricular nodal re-entrant tachycardia is a re-entry in the area of the atrioventricular node. Although rare, atrioventricular dissociation can occur because the atria and ventricles are not necessary for the re-entry circuit. This tachycardia may present at any age and familial forms have been described. It can trigger atrial fibrillation.

Changes have been made to its treatment. For acute management, the guidelines recommend the following approach, in this order: vagal maneuvers, adenosine administration (6-18mg iv bolus), and diltiazem/verapamil or BBs if the first 2 steps are ineffective. The initial results with intranasal etripamil are promising.

For chronic management, catheter ablation is the treatment of choice (I B) at all ages, due to its high success rate (97%) and low risk of atrioventricular block (< 1%). Slow-pathway modification is the objective, although it may sometimes be necessary to approach the target from the left septal side.

Catheter ablation has a higher risk of atrioventricular block in adults with congenital heart diseases and in patients with a baseline prolonged PR interval.

Cryoablation has a lower risk of iatrogenic atrioventricular block but is associated with a higher recurrence rate. Drug therapy is reserved for patients who refuse ablation (IIa B). The guidelines only refer to BBs and diltiazem/verapamil. Understandably, there is no mention of class III antiarrhythmic agents, but it is surprising that flecainide and propafenone are not considered options.

The pill in the pocket option has also disappeared; this strategy could be useful for some patients who do not wish to undergo ablation. Etripamil might one day be an alternative.

The guidelines specify that patients with minimal symptoms and short-lived and infrequent tachycardias can be managed without any treatment and through follow-up alone.

This arrhythmia is uncommon. It is caused by increased automaticity at the atrioventricular node or His bundle. Amiodarone is the drug of choice to prevent and treat this type of tachycardia after cardiac surgery. Ablation is less effective than for re-entrant tachycardia, with a 5% to 10% risk of atrioventricular block; cryoablation is safer than radiofrequency ablation.

The most important aspect of these guidelines is the confirmation of catheter ablation as the long-term treatment of choice for the vast majority of patients, due to its high effectiveness and low complication rate, instead of medical therapy. Also updated are the use of drugs for both acute and chronic management and the treatment of patients with asymptomatic pre-excitation.

Atrioventricular re-entrant tachycardia is by far the most frequent atrioventricular arrhythmia in patients with accessory pathways, particularly the orthodromic form (> 90%). In this type of tachycardia, the re-entrant impulse conducts from the atria to the ventricles via the specialized conduction system and then returns via the accessory pathway. This mechanism underlies 20% to 30% of all sustained SVTs. The antidromic form, with the circuit inverted with respect to the previous one and, therefore, with wide QRS (fully pre-excited), occurs in just 3% to 8% of patients with Wolff-Parkinson-White syndrome. In the case of other tachycardias (atrial or intranodal), the accessory pathway generates an abnormal ventricular activation without being part of the circuit (called a bystander accessory pathway). This is the case in atrial fibrillation, which frequently occurs in patients with Wolff-Parkinson-White syndrome, often due to degeneration from rapid re-entrant tachycardia. If the accessory pathway has a short refractory period, it is a potentially lethal arrhythmia due to its possible degeneration into ventricular fibrillation.

After vagal maneuver failure, intravenous adenosine is the acute therapy of choice in hemodynamically stable patients with orthodromic tachycardias. It is important to remember that electrical cardioversion may be required due to the possible induction of atrial fibrillation in patients with an antegrade conduction pathway. If adenosine fails, the calcium antagonists verapamil and diltiazem are the next option, due to the availability of more supporting evidence than for BBs. In antidromic forms, drugs acting on this pathway (ibutilide, procainamide, or flecainide) are preferred due to their better safety than those acting on the atrioventricular node, although electrical cardioversion is placed here in the same treatment line as the drugs. No mention is made of drugs such as sotalol or amiodarone, except the latter in relation to the refractory antidromic form and with a low recommendation level, or the pill in the pocket strategy. In pre-excited atrial fibrillation, atrioventricular node-blocking drugs are ruled out, and ibutilide and procainamide are the drugs of choice, ahead of flecainide and propafenone, which further slow nodal conduction. Amiodarone is contraindicated in this context because of the proven risk of ventricular fibrillation. Electrical cardioversion should be considered at early stages.

Catheter ablation is the chronic therapy of choice in patients with symptomatic recurrent or “at risk” episodes. Drugs are the clear second-line approach (when ablation is not possible or has failed or according to patient preference). In this regard, diltiazem, verapamil, and BBs would be the drugs of choice in the orthodromic forms without pre-excitation, whereas propafenone and flecainide are preferable in patients with pre-excitation but without structural heart disease.

The new guidelines are more favorable to interventional approaches in asymptomatic patients with pre-excitation. Their risk of sudden cardiac death is estimated to be 2.4/1000 person-years. Based on the analysis of various studies, an electrophysiological study should be performed at baseline and during isoproterenol infusion in competitive athletes and people with high-risk occupations, such as pilots or professional drivers, as well as ablation of the abnormal pathway if it shows signs of risk, such as a minimum R-R interval during atrial fibrillation ≤ 250ms, an antegrade refractory period ≤ 250ms, an inducible tachycardia mediated by this pathway, or the presence of multiple accessory pathways. In other situations, the recommendation for an invasive study is less consistent and should always depend on consideration of its pros and cons with patients and their relatives. The recommendation level of noninvasive studies (sudden disappearance of pre-excitation during the stress test or during perfusion of group I antiarrhythmics or intermittent pre-excitation) has been downgraded because these abnormal pathways are sensitive to catecholamines and their electrical properties improve in situations of sympathetic hypertonia, which gives these findings a low predictive value. If the indication for ablation is doubtful, a pathway location in the septal region near the atrioventricular node may help to rule it out or indicate cryoablation, assuming that the lower risk of atrioventricular block is offset by a higher recurrence rate. Preventive ablation is not recommended for asymptomatic Mahaim-type pathways because their decremental properties somewhat “protect” against sudden cardiac death. However, ablation is indicated for tachycardia-induced cardiomyopathy secondary to pre-excitation-induced ventricular dyssynchrony. Clinical follow-up is recommended in patients with asymptomatic pre-excitation and the absence of high-risk indicators at prognostic stratification (IIa).

The guidelines omit the diagnostic value of adenosine for patients with doubtful pre-excitation, although transient atrioventricular nodal block may rule out or confirm the presence of an abnormal pathway, whose management would be the same as that of a manifest pathway.