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............................................................... AVRT. The derived criteria were found to offer sensitivity of 75% and specificity of 100%,73 and the algorithm was also validated in another study,74 but experience is still limited. In fact, several independent studies have found that various ECGbased methods have specificities of 4080% and accuracies of 75%.44,68,7580 Indeed, a similar diagnostic accuracy of 75% would be achieved effortlessly by considering every wide QRS tachycardia to be a VT, because only 2530% are SVTs. Therefore, emerging approaches to integrate these algorithms and provide more accurate scoring systems are being evaluated.81 Furthermore, conventional ECG criteria have reduced the sensitivity to distinguish VT from SVT with aberrancy in patients with idiopathic VT. This is most pronounced in VTs originating from septal sites, particularly Purkinje sites and the septal outflow tract regions.82 9.2.2 Electrophysiology study On certain occasions, an EPS is necessary for diagnosis. 9.3 Irregular tachycardias An irregular ventricular rhythm most commonly indicates AF, multifocal AT, or focal AT/atrial flutter with variable AV conduction, and may occur in the context of both narrow and broad QRS complexes. When AF is associated with rapid ventricular rates, the irregularity of this ventricular response is less easily detected and can be misdiagnosed as a regular SVT.83 If the atrial rate exceeds the ventricular rate, then atrial flutter or AT (focal or multifocal) is usually present. Polymorphic VT and, rarely, monomorphic VT may also be irregular. Occasionally, a junctional, non-re-entrant tachycardia may have a variable rate. Specifically, the differential diagnosis of an irregular wide QRS tachycardia is either pre-excited AF or polymorphic VT, or AT with variable block in the context of aberrancy. Pre-excited AF manifests itself by irregularity, a varying QRS morphology, and a rapid ventricular rate (owing to the short RP of the AP). The changing QRS morphology results from varying degrees of fusion due to activation over both the AP and the AVN, which also result in variation in the width of the delta wave. A further cause of varying QRS morphology in this context will be if more than one antegrade AP is present with intermittent conduction over each. The ventricular rate tends to be higher than in those with non-preexcited AF.84 10 Acute management in the absence of an established diagnosis 10.1 Regular tachycardias 10.1.1 Narrow QRS (120 ms) tachycardias Patients with SVT are common and potentially recurrent attenders in emergency departments, with an estimated 50 000 visits each year in the USA.85 The initial approach to acute management tends to be non-drug-based, with escalation to intravenous (i.v.) drugs or electrical cardioversion in the absence of early correction (Figure 4). 10.1.1.1 Haemodynamically unstable patients Immediate direct-current (DC) cardioversion is the first choice in haemodynamically compromised patients with narrow QRS tachycardia.8688,101 10.1.1.2 Haemodynamically stable patients Vagal manoeuvres can be used to terminate an episode of narrow QRS SVT.41 The effectiveness of conventional vagal manoeuvres in terminating SVT, when correctly performed, has been reported as between 19 and 54%.41,8991,102,103 Vagal manoeuvres include different techniques used to stimulate the receptors in the internal carotid arteries. This stimulation causes a reflex stimulation of the vagus nerve, which results in the release of acetylcholine, which may in turn slow the electrical impulse through the AVN and slow the heart rate. Many of these manoeuvres can be performed with minimal risk at the bedside or in an office setting, and can be both diagnostic and therapeutic. The Valsalva manoeuvre is a safe and internationally recommended first-line emergency treatment for SVT, although a recent Cochrane review found insufficient evidence to support or refute its utility.89 The Valsalva manoeuvre has generally been shown to be most effective in adults, and in AVRT rather than AVNRT. A modified Recommendations for the acute management of narrow QRS tachycardia in the absence of an established diagnosis Recommendation Classa Levelb Haemodynamically unstable patients Synchronized DC cardioversion is recommended for haemodynamically unstable patients.8688 I B Haemodynamically stable patients A 12 lead ECG during tachycardia is recommended. I C Vagal manoeuvres, preferably in the supine position with leg elevation, are recommended.41,8991 I B Adenosine (618 mg i.v. bolus) is recommended if vagal manoeuvres fail.9294 I B Verapamil or diltiazem (i.v.) should be considered, if vagal manoeuvres and adenosine fail.92,9498 IIa B Beta-blockers (i.v. esmolol or metoprolol) should be considered if vagal manoeuvres and adenosine fail.97,99,100 IIa C Synchronized direct-current cardioversion is recommended when drug therapy fails to convert or control the tachycardia.87,88 I B i.v. beta-blockers are contraindicated in the presence of decompensated HF. i.v. verapamil and diltiazem are contraindicated in the presence of hypotension or HFrEF. DC = direct current; ECG = electrocardiogram; HF = heart failure; HFrEF = heart failure with reduced ejection fraction; i.v. = intravenous. aClass of recommendation. bLevel of evidence. Downloaded from academic.oup.com/eurheartj/article/41/5/655/5556821 by guest on 07 October 2026