Supraventricular tachycardia (SVT)

      Supraventricular tachycardia (SVT) is a cardiac arrhythmia arising from improper electrical activity of the heart. It is a type of tachycardia (rapid heart rhythm) originating at or above the atrioventricular node. It can be contrasted with the potentially more dangerous ventricular tachycardias—rapid rhythms that originate within the ventricular tissue.Its mainly caused by re-entry mechanism.reentry means, "the circular propagation of an impulse around 2 interconnected pathways with different conduction characteristics and refractory periods". In SVT the heart rate goes high by any abnormal electrical impulse originated in the atria. In this the heart beats so rapidly so that the heart muscles does not relax adequately in between each contractions. When the heart chambers do not relax adequately, they may not contract properly or fill with enough blood adequate for the whole body pumped out by the next beat. Especially when the oxygen demand is high when the body is in action or the mind is in stress.

Common types of  SVT

Presentation

1. Palpitation    
2. Dizziness
3.  Shortness of breath
4.  Syncope
5. Chest pain
6. Fatigue
7. Diaphoresis
8.  Nausea  

      

       Diagnostic investigations 

              

              

1. ECG- help to determine tachyarrythmic classifications 
• Sinus tachycardia- HR more than 100bpm
• atrial tachycardia- more than 125bpm with long RP wave
• atrial flutter- between 200-300bpm
• atrial fibrillation- irregularly regular and no P waves)
2. Cadiac biomarkers
3. Serum electrolytes
4. Complete blood count
5. Chest X-ray 
6. Transthoracic echocardiography

Management

Short-term
Adenosine (Adenocard)	V: endogenous purine nucleotide	Terminates SVT	6 mg rapid intravenous push, repeat with 12 mg if needed	Can be diagnostic and therapeutic
				Extremely short half-life
				Adverse effects include chest pain and dyspnea during administration
				Contraindicated in patients with Wolff-Parkinson-White syndrome
Diltiazem	IV: calcium channel blocker	Decreases rate	0.25 mg per kg intravenous bolus	Adverse effects include dizziness, heart failure exacerbation
				Avoid in patients with Wolff-Parkinson-White syndrome or wide complex tachycardia
Esmolol (Brevibloc)	II: beta blocker	Decreases rate	500 mcg per kg intravenous loading dose	Can be proarrhythmic; has short half-life
				Avoid in patients with renal disease; use with care in patients with asthma
Verapamil	IV: calcium channel blocker	Decreases rate	5 mg intravenously, up to 15 mg	Avoid in patients with congestive heart failure, Wolff-Parkinson-White syndrome, wide complex tachycardia, or atrioventricular block (second or third degree)
Long-term
Amiodarone(Cordarone)	III: potassium channel blocker*	Prevents SVT	200 to 400 mg orally once daily	Can result in optic neuritis, thyroid dysfunction, pulmonary fibrosis
Disopyramide (Norpace)	Ia: sodium channel blocker*†	Prevents SVT	200 to 400 mg orally twice daily	Adverse effects include urinary retention
Metoprolol	II: beta blocker	Decreases rate	25 to 100 mg orally twice daily	Atrioventricular node suppression possible
Procainamide	Ia: sodium channel blocker	Prevents SVT(long-term use)	250 to 500 mg orally every six hours	Adverse effects include lupus, hypotension, His-Purkinje block
Quinidine	Ia: sodium channel blocker*†	Prevents SVT(long-term use)	324 to 648 mg orally every eight to 12 hours	Avoid in patients with atrial fibrillation because of increased mortality
				Closely monitor QTc interval when initiating therapy
Verapamil	IV: calcium channel blocker	Prevents SVT	80 to 240 mg orally three times daily	Adverse effects include constipation, dizziness
				Avoid in patients with Wolff-Parkinson-White syndrome or wide complex tachycardia

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Long-term Management of SVT

       References 
       

• Klein, G.J., Sharma, A.D., Yee, R. & Guiraudon, G.M. 1987, 'Classification of supraventricular tachycardias', Am J Cardiol., vol. 60, no.6, pp. 27D-31D.
• Levy, S. & Ricard, P. 1997, 'Using the right drug: a treatment algorithm for regular supraventricular tachycardias', Eur Heart J, vol. 18, Suppl C, pp. C27-32
• Mitchell, L.B. 2015a, 'Reentrant Supraventricular Tachycardias (SVT, PSVT)', retrieved 28 April 2015, <http://www.merckmanuals.com/professional/cardiovascular-disorders/arrhythmias-and-conduction-disorders/reentrant-supraventricular-tachycardias-svt-psvt>
• Mitchell, L.B. 2015b, 'Overview of arrythmias', retrieved 28 April 2015, <http://www.merckmanuals.com/professional/cardiovascular-disorders/arrhythmias-and-conduction-disorders/overview-of-arrhythmias#v936668>