I47.1
Usually paroxysmal.
Often young patients with normal hearts.
AV nodal re-entry or atrioventricular re-entry (WPW syndrome).
P waves usually not visible (hidden by QRS complexes).
GENERAL MEASURES
Vagal manoeuvres: The modified Valsalva manoeuvre is the most effective – it should be done semi-recumbent with 15 seconds of strain, followed immediately by supine positioning and passive leg raising.
Carotid sinus massage.
Should be done with the patient supine and as relaxed as possible.
MEDICINE TREATMENT
Initial therapy
If vagal manoeuvres fail:
- Adenosine, rapid IV bolus, 6 mg.
- Follow by a bolus of 10 mL sodium chloride 0.9% to ensure that it reaches the heart before it is broken down.
- Half life: ± 10 seconds.
- Run the ECG for 1 minute after the injection as a recording of method of cessation may be helpful diagnostically.
- If 6 mg fails, repeat with 12 mg.
- If this fails, repeat with another 12 mg.
- If the medicine reaches the central circulation before it is broken down the patient will experience flushing, sometimes chest pain, wheezing and anxiety.
- If the tachycardia fails to terminate without the patient experiencing those symptoms, the medicine did not reach the heart.
If none of the above is effective or if the patient is hypotensive, consider synchronised cardioversion.
Note: Adenosine is contraindicated when atrial flutter is the obvious diagnosis, administration of adenosine can precipitate 1:1 conduction at ventricular rates 250–360 bpm and should be avoided.
Long term therapy
Teach the patient to perform vagal manoeuvres. Valsalva is the most effective.
For infrequent, non-incapacitating symptoms:
- Cardio-selective ß–blocker, e.g.:
- Atenolol, oral, 50–100 mg daily.
If asthmatic, without heart failure:
- Verapamil, oral, 40–120 mg 8 hourly.
Verapamil and digoxin are contraindicated in WPW syndrome.
REFERRAL
If the patient continues to experience debilitating symptoms refer for radiofrequency ablation.