{"id":835,"date":"2020-10-16T12:51:02","date_gmt":"2020-10-16T19:51:02","guid":{"rendered":"https:\/\/dhs.lacounty.gov\/emergency-medical-services-agency\/?page_id=835"},"modified":"2026-05-26T12:21:29","modified_gmt":"2026-05-26T19:21:29","slug":"emergency-medical-services-ce29","status":"publish","type":"page","link":"https:\/\/dhs.lacounty.gov\/emergency-medical-services-agency\/home\/emergi-press\/emergency-medical-services-ce29\/","title":{"rendered":"EMERGENCY MEDICAL SERVICES-CE29"},"content":{"rendered":"

[vc_row][vc_column][vc_column_text css=””]<\/p>\n

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ECG OF THE MONTH \u2013 July\/August 2025<\/strong><\/p>\n

Case:<\/h1>\n

It\u2019s August, the height of fire season! Paramedics respond to the scene of a CalFire wildfire co-response for a 21-year-old CalFire Conservation Camp worker complaining of syncope. Upon your arrival to the staging area, you see a male sitting on the grass. He is mildly \u00a0tachypneic and states that he passed out while using hand tools for spot fire suppression near the fire line. His supervisor states that he was unresponsive for approximately 35 seconds, then quickly regained a normal mental status. He reports feeling dizzy for the past two days and has been drinking significant amounts of water while participating in high-intensity activity battling the fire for the past week. This is his first fire assignment as an inmate worker, and he did not report his earlier symptoms as he wanted to \u201cmake a good impression\u201d on his supervisor.<\/p>\n

Vital signs<\/u>: BP 86\/60, HR 78, RR 26, SpO\u2082 100% on room air<\/p>\n

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[\/vc_column_text][\/vc_column][\/vc_row][vc_row][vc_column][vc_tta_accordion][vc_tta_section title=”1. WHAT IS YOUR INTERPRETATION OF THIS ECG?” tab_id=”1602848468801-c6df3840-2d2d”][vc_column_text css=””]Rate:<\/strong>\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 91 bpm<\/p>\n

Rhythm:<\/strong>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Normal Sinus Rhythm<\/p>\n

ST Segment Elevation >1mm
\nIn 2 or more contiguous
\nLeads?:<\/strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 No<\/p>\n

Other notable findings:<\/strong> Prominent U-waves in precordial leads (V2-V5), long QU interval (QT interval+ U wave).[\/vc_column_text][\/vc_tta_section][vc_tta_section title=”2. LEARN MORE ABOUT THIS EKG PATTERN:” tab_id=”1602848468870-8461451f-5b0c”][vc_column_text css=””]Question: What electrolyte abnormality is associated with these prominent U waves?<\/em><\/strong><\/p>\n

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  1. Hypernatremia<\/li>\n
  2. Hyperkalemia<\/li>\n
  3. Hyponatremia<\/li>\n
  4. Hypokalemia \u2705<\/li>\n<\/ol>\n

    Answer: Moderate to severe hypokalemia is classically associated with prominent U waves and a prolonged QU interval — the interval from the start of the QRS interval to the end of the U wave — that is longer than \u00bd the distance between adjacent QRS complexes.<\/p>\n

    This patient is suffering from critical hypokalemia secondary to heat exhaustion. He is likely hypovolemic due to volume loss from excessive sweating. Along with water loss, heavy sweating also results in salt loss and can lead to low potassium levels in the blood. Incomplete electrolyte repletion throughout the week has allowed potassium levels to drop progressively. If the patient has been drinking water only and not consuming adequate amounts of salt-containing foods, the body will be unable to replace the lost potassium. The prominent U waves and prolonged QU interval are ECG signs of hypokalemia.<\/p>\n

    Treatment per protocol 1222 should involve cooling the patient and, in this case, volume expansion with normal saline to help replete the lost water and salt. Although potassium repletion will be needed, LA County EMS crews do not carry potassium-containing fluids; this will be initiated upon arrival at the emergency department.[\/vc_column_text][\/vc_tta_section][vc_tta_section title=”3. The Case Continues:” tab_id=”1602848532145-5bb45b07-dfaf”][vc_column_text css=””]While you are treating the patient, he complains of dizziness and says he thinks he is going to pass out again. You capture an ECG and obtain the following result:<\/p>\n

    \"\"<\/p>\n

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    Question: What rhythm seen in this ECG may be precipitated by severe hypokalemia?<\/p>\n

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    1. Atrial fibrillation with RVR<\/li>\n
    2. Sinus tachycardia<\/li>\n
    3. Torsades de Pointes \u2705<\/li>\n
    4. Ventricular fibrillation<\/li>\n<\/ol>\n

      Answer: Torsades de Pointes (TdP) is a form of polymorphic ventricular tachycardia caused by a prolonged QT interval. In this case, a premature atrial contraction likely led to R-on-T phenomenon (where a premature beat occurs while the heart is depolarizing from the last heartbeat, landing on the T wave of the preceding beat), triggering TdP. The characteristic morphology of the QRS complex twisting around the isoelectric line is dramatically seen in the following example:<\/p>\n

      \"\"<\/p>\n

      You recognize this as TdP and immediately perform synchronized cardioversion at 120 J due to the patient being hypotensive and lacking IV access. The patient converts back to sinus rhythm and is transported to the hospital in stable condition.<\/p>\n

      After base contact is made, the patient is transported to the MAR where he is diagnosed with heat exhaustion and severe hypokalemia. His serum potassium level is 1.9, well below the normal range of 3.5-5.<\/p>\n

      Torsades de Pointes is treated in the hospital with magnesium infusion and defibrillation if the patient is pulseless, unstable, or the rhythm does not resolve. Although defibrillating a patient with a pulse may seem unusual, the polymorphic nature of the VT makes true synchronization impossible, so defibrillation is the appropriate electrical therapy.<\/p>\n

      Magnesium is believed to stabilize the heart\u2019s electrical activity, though the exact mechanism remains unclear. [1][\/vc_column_text][\/vc_tta_section][vc_tta_section title=”Take-Away Points” tab_id=”1659731556331-eba8d5c0-f722″][vc_column_text css=””]<\/p>\n

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      • Excessive exertion and sweating without appropriate repletion may lead to dangerous electrolyte abnormalities due to salt wasting.<\/li>\n
      • Prominent U waves and prolonged QU interval are classic indicators of hypokalemia.<\/li>\n
      • Torsades de Pointes (TdP) is a potentially deadly rhythm that can result from critical hypokalemia. It is treated via protocol 1213.<\/li>\n<\/ul>\n

        [\/vc_column_text][\/vc_tta_section][\/vc_tta_accordion][\/vc_column][\/vc_row][vc_row][vc_column][vc_column_text css=””]References<\/strong><\/p>\n

        ECGs and rhythm strips are courtesy of Dr. James Niemann and Life in the Fast Lane:<\/p>\n

        Hypokalaemia<\/a><\/p><\/blockquote>\n