Case Studies

Case 2: An elderly woman with a racing heart

You are a foundation year house officer in geriatric medicine. One of your patients, a 98-year-old woman, was admitted from her nursing home with a cough productive of green sputum. She is currently being treated for community-acquired pneumonia with co-amoxiclav and clarithromycin. Three days later, she develops diarrhoea and on the consultant ward round, she complains of a ‘racing heart’. The consultant examines her and finds that her mucous membranes are dry and her pulse is 120 irregular. Auscultation of her chest reveals minimal crackles at the left base, and her heart sounds are normal. You ask one of the nurses to record an ECG. You review the ECG and note that the rhythm is irregularly irregular and that P waves are absent. You recall that her admission ECG showed normal sinus rhythm with old ischaemic changes (T wave inversion in V3–V6). You take blood and send it for a full blood count, urea and electrolytes, and C-reactive protein (CRP). You review the bloods and note that the white cell count and CRP are improving but the potassium is 3.0 (normal range 3.5–5.5 mmol/L).

• 1. What is the new ECG rhythm?

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  This patient is now in atrial fibrillation (AF) with a fast ventricular response. Fast because the rate is greater than 100. Atrial fibrillation because the rhythm is irregularly irregular and there are no P waves; recall that the P wave represents organized atrial depolarization and thus contraction.

• 2. What is the likeliest cause of this woman’s arrhythmia?

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  The likeliest causes of this patient’s arrhythmia are hypokalaemia and dehydration secondary to diarrhoea.

• 3. Why has this woman developed diarrhoea?

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  This patient has most likely developed diarrhoea secondary to the antibiotics that she was receiving for her pneumonia.

• 4. How do you treat this patient?

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  Her serum K+ and other electrolytes must be corrected. In many cases oral potassium supplements are most appro-priate, however, her dry mucous membranes suggest she is dehydrated – a slow bag of intravenous fluids containing 40 mmol/L potassium should be considered in this case. Stopping her antibiotics should be discussed with a microbiologist. Although these reversible factors likely precipitated this episode of AF, her ECG suggests underlying ischaemic heart disease. She may have paroxysmal AF and may not revert to sinus rhythm once her electrolytes are corrected. The long-term management of paroxysmal atrial fibrillation is with anticoagulants (although this is inappropriate if she is at high risk of falls), and either rhythm-control or rate-control agents.