Makindo Medical Notes.com

Related Subjects: |Wolff-Parkinson White syndrome (WPW) AVRT |Lown Ganong Levine Syndrome AVRT |Supraventricular Tachycardia (SVT) |Atrioventricular Nodal Reentrant Tachycardia AVNRT |Atrial Flutter |Atrial Fibrillation |Sinus Tachycardia |Sinus Arrhythmia |Multifocal Atrial Tachycardia |Resuscitation - Adult Tachycardia Algorithm

About

• Any tachycardia arising from above the level of the Bundle of His.
• Usually refers to those which are reentrant around the node
• Those where the reentry pathways is beyond the node are AVRT
• AVRT are WPW and Long Ganong Levin syndrome

Aetiology of AVNRT

• Needs two pathways A and B around a central point or the AV node
• Slow Pathway with short refractory period
• Long Pathway with long refractory period
• Atrial ectopics travels down slow and up fast like a catherine wheel firework sending off depolarisation to ventricles and possible retrogradely to atria

Classify

• Slow-Fast is commonest > 90% % RP' < P'R
• Fast-Slow 10-15% RP' > P'R
• Slow-Slow < 5%

Diagram showing AVNRT

Clinical

• Seen all ages. Benign. Often young. Females > Males at 2:1.
• Symptoms presyncope, breathless, dizziness.
• Chest pain occasionally. With palpitations.
• Can be misdiagnosed as panic attack. Diagnosis delayed for years.
• Possible role for stress, caffeine, alcohol, smoking, drugs

Investigations

• FBC, U&E, TFTs, LFTs, CXR
• 12 lead ECG during episode: this is the most helpful diagnostic tool. May be SR by the time seen in ED. 95% slow fast may show narrow complex tachycardia rate 120-240/min. Most types of SVT have narrow QRS complexes. Wide complex tachyarrhythmias can also occur and can be secondary to SVT associated with bundle branch block or an accessory pathway. Always consider if it could be ventricular tachycardia and take expert advice.
• Implantable recorder if transient non captured
• Exclude Phaeochromocytoma if HTN but this is rare
• Echocardiogram to exclude structural disease where there are concerns
• ECG Findings
• Narrow complex tachycardia rates of 120 to 240 bpm. May be Bundle branch block and mimic VT

Clinical Pearls

• Sudden onset and termination suggests PSVT
• “Shirt flapping" or “neck pounding" Suggests AVNRT
• Hypotension/syncope/presyncope - indicates that SVT is poorly tolerated and suggests need for treatment and referral to a specialist.
• Presence of underlying structural heart disease suggests atrial tachycardia
• Preexcitation (AVRT) refer to an arrhythmia specialist for ablation

Examples

Management

• ABC if needed. IV access. Immediate DC countershock if unstable otherwise consider vagal maneouvres or drugs. The ECG will show a narrow complex tachycardia usually at > 150/min, If exactly 150/min consider Atrial flutter and adenosine will show flutter waves more clearly but may not terminate it.
• If suspect SVT but a broad complex due to aberrant conduction or accessory pathway then be very cautious and get expert advice. Avoid verapamil/Diltiazem. If unstable DC shock for either and Amiodarone may be useful.
• Stop the circuit by increasing vagal tone by Carotid sinus massage or Vagal Manoeuvres or Valsalva if fails then Adenosine or Verapamil
• Adenosine IV rapid 6 -24 mg fast bolus. Start with a lower dose 1-3 mg if heart transplant or central line or taking dipyridamole. Warn patients they will temporarily feel awful but it will pass.
• Verapamil 2.5-5 mg slow IV if narrow complex. Further doses may be needed. Diltiazem IV may be used where available.
• Pre-excited AF seen with AVRT: IF suspect AF and Aberrant conduction down the accessory pathways avoid Adenosine, Digoxin, Beta Blockers or Calcium Channel blocker. Consider IV Flecainide Or IV Propafenone or IV Amiodarone or Cardioversion if unstable. Rate often 200-300. The QRS is irregular and varying QRS morphology. Patients presenting with pre-excited AF should be referred for catheter ablation of the accessory pathway, not only to eliminate symptoms of palpitations but also to eliminate the risk of sudden death. The accessory pathway responsible for pre-excited AF or supraventricular tachycardia can be eliminated in about 95% of patients with a low risk of complications (1%). See WPW
• Anecdotal evidence for IV magnesium.
• Long term consider referral to cardiac electrophysiologist for nodal ablation

References

• SVT toolkit from ACC
• Common Types of SupraventricularTachycardia: Diagnosis and Management