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Stem
A 24-year-old woman presents to the emergency department with a 2-hour history of sudden-onset palpitations that began while she was watching television. She describes a rapid, regular "fluttering" in her chest and neck, associated with lightheadedness, breathlessness and chest tightness. She has had three similar episodes over the past year, each stopping suddenly — and she notes that she urinated several times after the last episode resolved. She is otherwise fit and well, takes no regular medication, and does not smoke. On examination: pulse 180 bpm, regular, blood pressure 100/64 mmHg, oxygen saturation 98% on air, respiratory rate 18, and she is alert and conversant. The JVP shows prominent regular cannon A waves. A 12-lead ECG shows a regular narrow-complex tachycardia at 180 bpm with no clearly visible P waves and a pseudo R-prime in V1.
Questions
a) What is the most likely diagnosis, and give three ECG features that support it? (2 marks)
Likely diagnosis: AV nodal re-entrant tachycardia (AVNRT), the commonest regular supraventricular tachyarrhythmia. Supporting ECG features: regular narrow-complex tachycardia (QRS under 0.12 s); RP interval at or under 90 ms favours AVNRT (retrograde P buried in the QRS); pseudo R-prime in V1 and/or pseudo S waves in the inferior leads; pseudo-r′ in aVR is a more accurate newer sign. The frog sign (regular cannon A waves in the JVP) further supports AVNRT.
b) Outline your immediate stepwise management in the emergency department. (4 marks)
- ABCDE assessment: high-flow oxygen if hypoxic, attach continuous cardiac monitoring and a defibrillator, establish IV access, and record a 12-lead ECG. She is haemodynamically stable (BP maintained, alert, no syncope/ischaemic pain/heart failure), so proceed to the drug ladder rather than cardioversion.
- Vagal manoeuvres first: perform the modified Valsalva manoeuvre (REVERT protocol) — semi-recumbent at 45 degrees, a 15-second forced strain to about 40 mmHg, then supine with legs raised to 45 degrees for 15 seconds. Record an ECG throughout.
- If unsuccessful, IV adenosine: 6 mg rapid IV bolus, then 12 mg if necessary (the randomised dose-ranging regimen — cumulative response 57.4% then 93.4%; average time to termination 30 seconds). Warn that adverse effects occurred in 36% of patients, lasted less than 1 minute, and were usually mild.
- If adenosine fails or should be avoided (e.g. asthma — bronchoconstriction in both asthmatics of a 26-patient series): IV verapamil 5 mg, then 7.5 mg if necessary (cumulative 81.3% then 91.4%). If still in SVT: IV amiodarone (PSVT conversion 61% in one CCU series) or synchronised DC cardioversion under sedation. Unstable SVT at any point = synchronised DC cardioversion, the therapy of choice when there is haemodynamic compromise. [1][2][12][11]
c) Name two contraindications to adenosine and two drugs that interact with its dosing. (2 marks)
Asthma: adenosine caused bronchoconstriction in the only two asthmatics among 26 treated — consider alternatives. Numeric transplant/dipyridamole dose reductions are conventional teaching and were not verified here. WPW with pre-excited AF: AV-nodal blockers (including adenosine) can increase the ventricular rate and have precipitated VF — that is a true contraindication to adenosine in this setting.
d) What definitive long-term treatment would you offer, and why? What would change your acute management if her ECG in sinus rhythm showed a delta wave and short PR? (2 marks)
Definitive long-term treatment is slow-pathway catheter ablation for AVNRT: acute success 95%, long-term efficacy 93% over a mean 53 months. If her sinus-rhythm ECG showed a short PR with a delta wave (WPW pattern), the acute narrow-complex tachycardia could be orthodromic AVRT — vagal manoeuvres and adenosine remain appropriate while it is regular and narrow. The critical change is pre-excited atrial fibrillation (irregular broad-complex tachycardia): AV-nodal blockers are contraindicated (VF after AV-nodal blockade is described); electrical cardioversion is first-line, then accessory-pathway ablation (treatment of choice after sudden-death survival; first long-term option for 88% in a 17-country registry).