Missed Dialysis and a Widening QRS
A 61-year-old woman with type 2 diabetes and stage 4 chronic kidney disease (baseline creatinine 3.4 mg/dL) is admitted with nausea and generalized weakness. She missed two hemodialysis sessions, and the chemistry panel sent 25 minutes ago is still pending; yesterday's potassium was 5.2 mmol/L. A 12-lead ECG is obtained: sinus rhythm at 88 beats/min, PR 236 ms, QRS 132 ms and diffusely widened, tall symmetric T waves in V2-V5 measuring 12 mm, flattened P waves in lead II, and no ST-segment elevation. The technician is asked to compare this with an ECG from 3 months ago: PR 168 ms, QRS 92 ms, T waves 4 mm. The patient is alert but says her legs feel 'like rubber.' Blood pressure is 148/86 mmHg, SpO2 96%. The nurse is preparing the dialysis line and asks the technician whether the tracing is 'just a bundle branch block.'
1. Identify the most likely cause of the conduction and repolarization changes and explain why they are not simply a new bundle branch block.
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Most likely cause: hyperkalemia until proven otherwise, given missed dialysis, stage 4 CKD, and a potassium of 5.2 mmol/L the day before.
Why the ECG fits hyperkalemia:
- PR prolongation (168 to 236 ms) reflects slowed atrial and AV nodal conduction.
- Flattened P waves in lead II are an early sign of atrial muscle effect.
- Diffuse QRS widening (92 to 132 ms) occurs because elevated extracellular potassium reduces the resting membrane potential and inactivates sodium channels, slowing phase 0 depolarization.
- Tall, symmetric, peaked T waves (12 mm) are the classic repolarization change.
- The changes are new compared with the prior ECG.
Why it is not just a bundle branch block:
- A new left bundle branch block produces a broad, notched R in I, aVL, V5, and V6 with rS or QS in V1, and it does not flatten P waves or produce peaked T waves.
- A bundle branch block would not explain the PR prolongation or the diffuse T-wave change.
- The QRS widening here is diffuse rather than confined to a typical right or left bundle morphology.
Mechanism to articulate: hyperkalemia first speeds repolarization (peaked T waves), then slows atrial and ventricular conduction (flat P, long PR, wide QRS), and can progress to a sine wave and ventricular fibrillation.
2. Rank the findings on this ECG by immediate danger and state what you would communicate and to whom.
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Ranking by immediate danger:
- QRS widening and loss of visible P waves - these signal impending sine-wave morphology and cardiac arrest, not the T-wave height alone.
- PR prolongation and flattened P waves - evidence of progressive conduction slowing.
- Peaked T waves - important but less immediately dangerous than a very wide QRS.
Communication: Report urgently to the responsible nurse and clinician, in person or by phone, using measured values rather than labels: 'Sinus rhythm at 88, PR 236 ms, QRS 132 ms and diffusely widened, P waves flattened, peaked T waves at 12 mm in V2-V5; prior QRS was 92 ms. She missed two dialysis sessions and the potassium is pending.'
What to anticipate:
- Immediate 12-lead ECG, IV access, and continuous monitoring with a defibrillator nearby.
- Orders for IV calcium, insulin with glucose, and urgent dialysis.
- Repeat ECG after treatment to document improvement.
Do not wait for the potassium result before reporting; the ECG is the urgent finding. The technician communicates and documents but does not independently order treatment.
3. How would you distinguish this from a drug effect such as a tricyclic antidepressant or flecainide?
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Tricyclic antidepressant effect: sinus tachycardia is common, QRS is widened, and there is often a terminal R wave in aVR greater than 3 mm with a rightward shift of the terminal QRS axis. Peaked T waves and flattened P waves are not typical.
Flecainide effect: QRS widening with right-axis deviation and a Brugada-like pattern in V1-V2; the drug is sodium-channel blocking and can produce wide-complex tachycardia. It does not usually produce peaked T waves or PR prolongation of this degree.
Hyperkalemia in this patient: the combination of peaked T waves, flattened P waves, PR prolongation, and progressive QRS widening in a patient with missed dialysis and CKD is more coherent than a single drug effect. The comparison ECG showing normal intervals 3 months earlier strengthens the metabolic explanation.
Practical approach: review the medication list for tricyclics, flecainide, or other sodium-channel blockers; check for a terminal R in aVR; and report both possibilities if the picture is mixed. Do not withhold the urgent report while sorting out the cause. The clinician will use the potassium, medication history, and response to treatment to confirm.