Case 07: Palpitations

Mr Harrison, a 62-year-old man with known hypertension, presents with a 3-month history of palpitations, occasional breathlessness on exertion (SOBOE), and one episode of pre-syncope. His resting ECG shows an irregularly irregular rhythm, absent P waves, and small fibrillatory f-waves — consistent with atrial fibrillation (AF).

Atrial fibrillation is the most common sustained cardiac arrhythmia. Its electrophysiological basis is multiple ectopic foci within the atria firing at rates of up to 600 impulses per minute, generating chaotic depolarisation. Because the AV node acts as a filter, ventricular conduction is irregular, producing the characteristic irregularly irregular RR intervals on ECG. Key ECG features: no discernible P waves, f-waves (small irregular fibrillatory oscillations between QRS complexes), and irregularly irregular QRS complexes.

Hypertension is the most common cause of AF: sustained high atrial wall tension causes structural remodelling (atrial dilation and fibrosis), creating a substrate for re-entrant circuits and ectopic foci. Other causes include ischaemic heart disease, valvular heart disease (particularly mitral stenosis), thyrotoxicosis, and excessive alcohol consumption.

AF management has three goals: (1) rate control to prevent tachycardia-induced cardiomyopathy (target resting HR <110 bpm; <80–90 bpm in LV dysfunction); (2) rhythm control via pharmacological cardioversion (antiarrhythmics) or electrical cardioversion (DC cardioversion synchronised to the R-wave to avoid T-wave period and ventricular fibrillation); and (3) stroke prevention with anticoagulation. CHA2DS2-VASc score determines anticoagulation need: males with score ≥1, females with score ≥2 require anticoagulants. Antiplatelets are NOT recommended as a substitute for anticoagulation in AF.

Direct oral anticoagulants (DOACs) — particularly dabigatran (direct thrombin inhibitor) and rivaroxaban (Factor Xa inhibitor) — are preferred over warfarin for most patients with AF, offering lower stroke risk, lower intracranial bleeding risk, no INR monitoring requirement, rapid onset, and fewer drug/food interactions. Warfarin remains preferred in mechanical heart valves, valvular AF (AF with mitral stenosis), severe renal or hepatic dysfunction, and antiphospholipid syndrome. Dabigatran has a reversal agent (idarucizumab). In pregnancy, low-molecular-weight heparin (e.g. enoxaparin) is used; DOACs and warfarin are contraindicated.

Electrical cardioversion delivers a controlled DC shock synchronised to the R-wave (to avoid the vulnerable T-wave period during which unsynchronised shock could trigger ventricular fibrillation). It briefly terminates all electrical activity, allowing the sinoatrial node to re-establish normal sinus rhythm. Success rate is approximately 75%. Risks include thromboembolic stroke (mural thrombus dislodgement — mitigated by anticoagulation), superficial burns, and occasionally failure requiring external pacing.

Radiofrequency ablation (RFA) is used when symptoms remain uncontrolled. A catheter is advanced via the femoral vein to the left atrium via trans-septal puncture. Radiofrequency energy ablates tissue around the pulmonary veins, creating electrical isolation scars that block ectopic impulses from reaching the atria. Complications include stroke, cardiac tamponade, pulmonary vein stenosis, and damage to adjacent structures (oesophagus, phrenic nerve).