Supra Ventricular Tachycardia Pathophysiology ECG features Management Authors

Supra. Ventricular Tachycardia : Pathophysiology, ECG features, Management Author(s): Geraldine Leong Level: Basic Academic Affiliation: Emergency Medicine Resident, Sing. Health Version No: 1. 0 Submitted: March 2012 Editors’ Review:

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4 Outline • Definition • Classification of tachyarrythmias • Pathophysiology • ECG features • Management principles in ED • Clinical scenario

5 Definition • Point of stimulation arises from above the bundle branches • 3 main features: – Regular – Narrow complex (QRS <120 ms) – Tachycardia

6 Classification Tachyarrythmias Narrow-complex Irregular Regular - fast atrial - sinus fibrillation tachycardia - atrial flutter with variable conduction - AVRT - multifocal atrial tachycardia - AVNRT - atrial flutter with 2: 1 conduction - junctional tachycardia Broad-complex • Ventricular Fibrillation • Ventricular Tachycardia • Any supraventricular tachycardias with aberrancy

7 Pathophysiology • 3 main mechanisms – Re-entrant dysrhythmias – Abnormal automaticity – Triggered dysrhythmias • Re-entrant dysrhythmias most commonly encountered mechanism

8 Mechanism of Re-entrant dysrhythmias

9 Paroxysmal SVTs Two types: • AVNRT (~60%) – AV nodal re-entrant tachycardia – Commonest type • AVRT (~30%) – AV re-entry tachycardia – A/w Accessory pathway – Eg. Wolf – Parkinson – White Syndrome

10 AVNRT

11 AVNRT: ECG features • Narrow complex, regular tachycardia • No P waves prior to QRS complexes • P waves are usually buried within QRS complex (but not always the case) • Rate is fixed – not like sinus tachycardia where rate demonstrates gradual variations over time in response to etiology and interventions

12 AVNRT ECGs

13 AVRT

14 AVRT: ECG features • Narrow complex, regular tachycardia • P wave likely visible on ECG and displaced/retrograde to QRS (may not be present all the time) • Otherwise features similar to AVNRT difficult to tell apart on ECG can only definitively diagnose with electrophysiology studies

15 AVRT ECGs

16 Management Principles • Assessment of patient • Treating the rhythm • Disposition of patient

17 Treating the rhythm • Haemodynamically unstable: – Sedate and synchronised cardioversion starting at 50 J and increasing energy level if unsuccessful • Haemodynamically stable: – Vagal maneuvers – Pharmacological methods – Synchronised DC cardioversion

18 Vagal Maneuvers • Valsava • Carotid Sinus massage

19 Pharmacologic Methods • AV nodal blocking agents – Adenosine – Calcium channel blockers like verapamil or diltiazem • Asscessory pathway blocking agents – Procainamide • Other agents – Amiodarone

20 Brief note about Adenosine • Most commonly used drug to abort SVTs • Very short half-life < 10 seconds • Given as a fast bolus via a large peripheral cannular in the cubital fossa followed immediately by a saline flush • Start with IV 6 mg bolus followed by another 12 mg and another 12 mg bolus if unsuccessful • Can be both diagnostic and theraputic

21 Disposition • Observe in ED for period of about 2 -4 hours • Repeat ECG to ensure in NSR • Follow up with cardiology for further electrophysiology studies • Patient education

22 Clinical Scenario Triage notes: 30 years old, Palpitations since 1 hour ago. A/w SOB Not in distress. ECG stat Examination: T 36. 5 BP 110/70 mm. Hg HR 180 bpm SPO 2 99% RA

23 ECG done….

24 Management • Dx SVT • Patient haemodynamically stable • Mx in monitored setting with regular parameters and cardiac monitor, attempt vagal maneauvers – failed proceed with chemical cardioversion with AV nodal blocking agent adenosine

25 Post Adenosine

26 Another similar ECG

27 Wolf-Parkinson-White Syndrome! 4 ECG features that characterize WPW: (1) PR interval < 0. 12 s (2) Delta wave (3) QRS complex >0. 12 s (4) Secondary ST-segment-T-wave changes directed opposite to the delta wave and QRS complex changes

28 WPW (con’t) • 2 types of Paroxysmal SVT in WPW: – Orthodromic (90%) see AVRT pattern Narrow QRS cplx without delta wave HR ~ 160 -220 in adults

29 WPW (con’t) • 2 types of Paroxysmal SVT in WPW: – Antidromic (10%) Rapid wide QRS complexes Difficult to distinguish from VT

30 WPW (con’t) Back to the pt… • Electrophysiologic study showed accessory pathway with retrograde conduction properties • Underwent transcatheter radiofrequency ablation • Well on follow up

31 Take home messages • SYNCHRONISED CARDIOVERSION for all unstable patients with SVT • Refer patient cardiologist for electrophysiologic studies • Patient education is important!

32 References • Sarah AS, Robert C. Tachydysrhythmias, Emerg Med Cli N Am 24 (2006) 11 -40 • Jacqueline D, Christopher H, Amal M, William J. The electrocardiogram in the patient with syncope, American Journal of Emergency Medicine (2007) 25, 688– 701

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