SVT

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Supraventricular tachycardia

Paroxysmal SVT

• Atrioventricular nodal re-entry tachycardia (AVNRT) 50-60%

• Atrioventricular re-entry tachycardia (AVRT) 30%

• Intra-atrial re-entry tachycardia

• Automatic atrial tachycardia

• Sinus nodal re-entry tachycardia

AVNRT

• Uncommon in childhood

• Typical heart rate: 150-250 beats/min

• ± Palpitations, lightheadness, near syncope. True syncope unusual

• Neck pounding virtually pathognomonic when present

• Antegrade conduction is usually via a slow pathway with retrograde conduction via a fast pathway. As a result atrial and ventricular activation are virtually simultaneous and p waves are not usually visible

• Acute management and diagnosis - see fig 1

AVRT

• Antegrade conduction is usually down the normal pathway with retrograde conduction via an accessory pathyway that is located along the mitral valve annulus.

• Because the accessory pathway only conducts in a retrograde direction it has no effect on the surface ECG (even in sinus rhythm)

• Acute management and diagnosis - see fig 1

Intra-atrial re-entry tachycardia

• Tends to paroxysmal rather than incessant

• Atrial rates usually <200/min

• Management similar to AF in the absence of antegrade accessory pathway conduction

Automatic atrial tachycardia

• Tends to be incessant rather than paroxysmal

• Atrial rates usually <200/min

• May present in absence of structural heart disease or obvious precipitants but commonly associated with:

  • catecholamine release

  • chronic lung disease

  • myocardial infarction

  • acute alcoholic binges

  • amphetamine or cocaine abuse

Treatment

• Difficult to manage with drugs

• Treat or eliminate precipitants

• Beta-blockers may slow atrial rate but rarely restore sinus rhythm

• Class IC agents and amiodarone may be helpful. Avoid flecainide in patients with coronary artery disease and use with caution in patients with LV dysfunction

Sinus node re-entry

May respond to vagal manoeuvres, adenosine, verapamil or digoxin (slow onset of action)

Wolff-Parkinson-White syndrome

• ECG appearances depend on the conduction pathway

• In sinus rhythm impulses are conducted down both the His-Purkinje system and the accessory pathway. The QRS complex is wide as a result of pre-excitation of the ventricle via the accessory pathway (results in delta wave). Short PR interval (ECG)

• If the patient develops an AVRT (the most common tachycardia) the QRS complexes are normal as antegrade conduction is via AV node and only retrograde conduction occurs via the accessory pathway (ECG). However if aberrancy develops (this may be rate-dependent) or the patient develops an antidromic AVRT the complexes will be wide.

• In AF impulses may be conducted down both the His-Purkinje system and the accessory pathway (QRS with delta wave), down the His-Purkinje system alone (normal QRS) or down the accessory pathway alone (broad QRS). Ventricular rates may be very high (>300/min) due to very rapid antegrade conduction down the accessory pathway. (ECG)

Wide complex tachycardia & WPW

• Treatment should be directed towards blocking conduction via the accessory pathway

• Adenosine only blocks the AV node and may increase conduction via the accessory pathway but because of its short half life it poses little risk unless it precipitates AF

• Verapamil is contraindicated. Its hypotensive effects may make patients haemodynamically unstable or even contribute to the onset of VF

• IV digoxin should not be give to patients with WPW and AF because in 1/3 of patients it may enhance antegrade accessory pathway conduction and also degeneration to VF

• If systolic BP ³90 mmHg give IV procainamide 10 mg/kg at £50 mg/min. Decrease the administration rate if hypotension develops. Depresses conduction across the accessory pathway, decreases ventricular rate and stabilizes patient. May also terminate wide complex tachycardia

• Patients with angina, heart failure or hypotension or unsuccessful pharmacotherapy should be DC cardioverted.

Multifocal atrial tachycardia

• Characterized by:

  • ³3 morphologically distinct non-sinus p waves

  • atrial rates of 100-130 beats/min

  • variable AV block

• Commonly associated with respiratory disease and congestive cardiac failure. Hypoxaemia frequent

• Exacerbated by:

  • Digoxin or theophylline toxicity

  • Hypokalaemia, hypomagnesaemia, hyponatraemia

Treatment

• Does not respond to DC cardioversion

• Treat precipitants

• Metoprolol or verapamil for rate control- occasionally restore sinus rhythm, as does amiodarone.

Further reading

Trohman RG. Supraventricular tachycardia: Implications for the Intensivist. Crit Care Medicine, 2000; 28:N129-35

©Charles Gomersall, October, 2009 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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