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Synchronised DC cardioversion is used in cases of SVT where there are adverse features (myocardial ischaemic, heart failure, syncope or shock) present.

In synchronised cardioversion, the electrical shock is delivered during ventricular depolarisation in the cardiac cycle. This is important to reduce the risk of the rhythm changing into a life-threatening cardiac arrest rhythm (e.g. VF)
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Synchronised DC cardioversion
QuestionChoice
Adenosine is contraindicated in poorly controlled asthmatics as it can cause bronchospasm. Therefore verapamil is often preferred in this cohort of patients who present with SVT if vagal manoeuvres fail
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Verapamil
QuestionChoice
Adenosine is a medication that induces a transient block at the AV node. It is used if vagal manoeuvres are unsuccessful, initially at a dose of 6mg
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Adenosine
QuestionChoice
Unsynchronised DC cardioversion (defibrillation) is used in cases of cardiac arrest in the presence of a shockable rhythm. The shock is delivered at any point in the cardiac cycle
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Unsynchronised DC cardioversion
QuestionChoice
The history and ECG findings are suggestive of a supraventricular tachycardia (SVT). In the absence of adverse features (myocardial ischaemia, heart failure, syncope or shock), the first-line management of an SVT is vagal manoeuvres. These aim to stimulate the vagus nerve to slow down the heart rate
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Valsalva manoeuvre
QuestionComment
Should really put in the adenosine option that adenosine is contraindicated in asthma patients as it causes bronchospasm...
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Initial management is usually Valsalva anyway and not adenosine......
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# Summary

Supraventricular Tachycardia (SVT) is an umbrella term for several arrhythmias originating above the ventricles, including AV re-entry tachycardia and AV nodal re-entry tachycardia. Atrial fibrillation, atrial flutter and sinus tachycardias are all technically SVTs but are usually considered separately. Emergency treatment of SVT if the patient is stable involves vagal manoeuvres then administering adenosine if these are not successful. If the patient is unstable, cardioversion should be attempted with a synchronised DC shock.

# Definition
 
A Supraventricular Tachycardia (SVT) is any rhythm with a fast heart rate (over 100bpm) that originates from anywhere in the heart above the level of the Bundle of His. Unless there is aberrant conduction (e.g. bundle branch block), these will be narrow complex (i.e. QRS width is less than 120ms).
 
Sinus tachycardia, Atrial Fibrillation, Atrial Flutter, AV Re-entry Tachycardia (AVRT) and AV Nodal Re-entry Tachycardia (AVNRT) are examples of SVTs. Sinus tachycardia, Atrial Fibrillation and Atrial Flutter are considered separately and have different emergency management.
 
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# Management 

**Unstable patients**
 
Patients with any of the following adverse features should be treated with a synchronised DC shock, which can be repeated if unsuccessful:

- Shock
- Syncope
- Heart Failure
- Myocardial Ischaemia (usually presenting as chest pain)

Patients who are conscious require sedation or anaesthesia prior to attempting cardioversion.

**Stable patients**

Patients with no adverse features should be treated initially with vagal manoeuvres, e.g. carotid sinus massage or the Valsalva manoeuvre (get the patient to blow into a 10ml syringe for 15-20 seconds)

If this fails, the next step is giving IV Adenosine 6mg, following this with 12mg then 18mg boluses if the previous one is unsuccessful. 

This should be done with continuous ECG monitoring.

If adenosine fails to terminate the SVT, verapamil or a beta-blocker could be tried, with DC cardioversion also an option if medical treatment is unsuccessful.

**Further information on Adenosine**
 
- Adenosine is a medication that works by temporarily blocking conduction through the AV node
- It is given as a rapid IV bolus over 1-3 seconds 
- Prior to administration, patients should be warned that they may experience difficulty breathing, chest tightness and flushing
- Because of the risk of bronchospasm, patients with asthma should not be given adenosine (verapamil should be used instead)
- In patients with a central line, a reduced dose of 3mg should be given

# References

[UK Resuscitation Council Adult Tachycardia Algorithm](https://www.resus.org.uk/sites/default/files/2021-04/Tachycardia%20Algorithm%202021.pdf)

[BNF Treatment Summary - Arrhythmias](https://bnf.nice.org.uk/treatment-summaries/arrhythmias/#paroxysmal-supraventricular-tachycardia)
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The Valsalva manoeuvre is the first-line treatment for stable supraventricular tachycardia, promoting vagal stimulation to restore normal heart rhythm.
A 22-year-old patient with a background of asthma is admitted with a four-hour history of palpitations.

His heart rate is 180bpm, blood pressure 110/68mmHg, respiratory rate 18, SpO2 98% on air

His ECG shows a heart rate of 183 bpm and a regular narrow complex tachycardia. The admission chest x-ray is clear, and troponin levels are normal.

Which of the following is the next best step in management?
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