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....................................... adrenergic activation and suppressed by L-type Ca2þ current blockade. • Re-entrant circuits may be microscopic or simulate foci by surface ‘breakthrough’ of transmural propagation. Thus, mapping may be inadequate to distinguish them from automatic/triggered activity. • The exact circuit of AVNRT, the most common regular arrhythmia in the human, remains unresolved. • The potential role of connexin proteins in AVNRT, and SVT in general, is under investigation. • Both invasive and non-invasive tests for the risk assessment of patients with asymptomatic pre-excitation have limitations, being dependent on the autonomic tone. More accurate risk-stratification models are needed. • The proper management of asymptomatic pre-excitation and strict catheter ablation indications have not been established. • The genetics of SVT have not been adequately studied. There has been evidence for familial forms of AVNRT, AVRT, sinus tachycardia, and AT, but data are scarce. • Novel electroanatomical mapping systems now allow the simultaneous visualization of activation and voltage. The implications that this may have on characterizing the tachycardia substrate, and not just the circuit, require future research. • Mathematical modelling and numerical analysis of recorded ECGs, using fast Fourier and Gaussian models, may be helpful for the future of artificial intelligence applications in the differential diagnosis of narrow and wide QRS-complex tachycardias, but experience is limited.

20 ‘What to do’ and ‘what not to do’ messages from the Guidelines

‘What to do’ messages Recommendations for the acute management of narrow QRS tachycardia in the absence of an established diagnosis

Recommendation Classa Levelb

Haemodynamically unstable patients Synchronized direct-current cardioversion is recommended for haemodynamically unstable patients. 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. I B Adenosine (618 mg i.v. bolus) is recommended if vagal manoeuvres fail. I B Synchronized direct-current cardioversion is recommended when drug therapy fails to convert or control the tachycardia. I B

Recommendations for the acute management of wide QRS tachycardia in the absence of an established diagnosis Haemodynamically unstable patients Synchronized direct-current cardioversion is recommended in haemodynamically unstable patients. 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. I C Synchronized direct-current cardioversion is recommended if drug therapy fails to convert or control the tachycardia. I B

Recommendations for the therapy of sinus tachycardias Inappropriate sinus tachycardia Evaluation and treatment of reversible causes is recommended.139,144,162 I C

Recommendations for the therapy of focal AT Acute therapy Haemodynamically unstable patients Synchronized DC cardioversion is recommended for haemodynamically unstable patients. I B Haemodynamically stable patients Synchronized DC cardioversion is recommended when drug therapy fails to convert or control the tachycardia. I B Chronic therapy Catheter ablation is recommended for recurrent focal AT, especially if incessant or causing tachycardiomyopathy. I B

Recommendations for the therapy of multifocal AT Acute therapy Treatment of an underlying condition is recommended as a first step, if feasible. I C

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