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Challenges in Clinical Electrocardiography |

Refractory Hypotension and “Ventricular Fibrillation” With Large U Waves After Overdose

Jon B. Cole, MD1,2; Samuel J. Stellpflug, MD1; Stephen W. Smith, MD2
[+] Author Affiliations
1Minnesota Poison Control System, Minneapolis, Minnesota
2Department of Emergency Medicine, Hennepin County Medical Center, Minneapolis, Minnesota
JAMA Intern Med. 2016;176(7):1007-1009. doi:10.1001/jamainternmed.2016.2065.
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A woman in her 50s with a medical history of depression, rheumatoid arthritis, hypertension, and pulmonary eosinophilia presented to a rural hospital with acute agitation following an overdose. She arrived drowsy with a blood pressure (BP) of 80/44 mm Hg. Naloxone was ineffective; she was subsequently intubated and started on an infusion of epinephrine, 0.25 µg/kg/min, and sedated with diazepam, 150 mg. She was transferred by helicopter to a tertiary care center. En route she suffered cardiac arrest secondary to reported ventricular fibrillation (VF), (not recorded), with return of spontaneous circulation after 10 chest compressions without defibrillation. On arrival the patient continued to experience refractory hypotension with systolic blood pressures (SBP) in the 70s. The patient received a bolus of 20% intravenous fat emulsion (IFE), 100 mL, with immediate hemodynamic improvement; her blood pressure 5 minutes after the IFE bolus was 115/66 mm Hg. An electrocardiogram (ECG) was obtained (Figure 1).

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Figure 1.
Patient Elecrocardiogram on Arrival to Tertiary Care Center

The 4 long thin vertical lines show the peak of the U wave in every lead. The black arrowheads in leads V2 and V3 show the largest U waves. The yellow arrowheads show the peak of the P wave in leads V1, V2, and II; it is clearly separate from the U wave. The blue arrowheads show the peak of the T wave in leads V2, V3 and (much less prominently) V4. The red arrowhead and thin horizontal lines show the PR interval. The thick horizontal lines show (in increasing order of length) the QT segment, QT interval, and QU interval. The circles in leads V5 and V6 show waves that could be mistaken for giant T-U waves; however, it is clear from comparison with leads V2 to V4 that the T wave is complete prior to the inscription of the large wave, which is therefore an isolated U wave.

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Figure 2.
Enlarged View of V1 and V2

This enlarged view (from Figure 1) demonstrates P waves that are almost completely fused into the preceding U waves. Lack of recognition of the P waves may lead to this ECG being misinterpreted as a junctional rhythm.

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Figure 3.
Second Electrocardiogram, With Serum Potassium, 3.0 mEq/L

U wave size is decreased with potassium correction.

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