Here are some useful questions to help you decide whether or not your patient is stable.
1. Does your patient have clinical evidence of a reduced cardiac output?
Are they peripherally shut down, sweaty, hypotensive or showing signs of confusion or drowsiness?
Have they had a syncopal event or transient loss of consciousness?
Patients with excessive tachycardias (>150 bpm) are more likely to be unstable.
2. Does your patient have chest pain?
This would suggest ischaemia due to inadequate perfusion.
Many patients with SVT have mild chest discomfort or tightness however and this does not always reflect instability.
3. Does your patient have signs of heart failure?
Are they breathless with pulmonary crepitations on auscultation?
Does they have peripheral or sacral oedema with evidence of liver engorgement and a raised JVP?
4. Simple measures you should apply to all unstable patients:
A venous gas should give you a reliable and prompt K+.
Assume hypomagnasemia if hypokalaemia exists.
Order a calcium level.
5. Simple principles to remember:
Learning bite
An unstable patient requires electrical cardioversion rather than drugs regardless of the underlying rhythm.