容易誤判的低血鉀心電圖表現：個案報告暨文獻回顧

Easily Misdiagnosed Signs of EKG in Hypokalemia: A Case Report and Literature Review

謝秉翰(Ping-Han Hsieh) ； 李慶威(Ching-Wei Lee)

《內科學誌》 31卷3期 (2020/06) Pp. 210-217

https://doi.org/10.6314/JIMT.202006_31(3).09

摘要

低血鉀是臨床上常見且容易忽略的電解質異常，其與心律不整，心臟衰竭，心肌梗塞病患死亡率息息相關。在較嚴重低血鉀（一般定義是＜3.0 meq或只是患者因低血鉀而出現症狀），往往因為症狀表現多樣化，心電圖變化不熟悉及與其他疾患相似處多而造成診斷延遲。臨床上利用肢導的Lead II及胸前導的V3即可觀察到大部分低血鉀心電圖變化。當低血鉀發生時，最早的心電圖為減少T波的高度，隨著鉀離子下降，出現ST段下降，T波反轉，並可能伴隨PR間距與P波的高度增加，以及典型U波，與T波融合產生的巨大U波。在血鉀濃度＜2.7mEq/L時，較可以預測在心電圖上會呈現出典型低血鉀表現。而ST段下降往往需在血鉀濃度較嚴重降低時才會出現，且往往合併U波與胸前導極Lead V1-V3 ST段下降的出現。偽QT間期延長現象往往也需與實際QT或QU間期延長做鑑別診斷。心跳快與血壓是低血鉀心電圖表現的干擾因子。嚴重的低血鉀會增加心肌細胞自動性（automaticity）與減慢傳導，如未給予即時治療，可能導致致命的心律不整。心電圖U波高度，ST下降幅度與T/U比率可增加低血鉀的診斷敏感度。且在心肌肥厚，心肌缺血，服用抗心律不整藥物等病患，也有相對應可參考的鑑別診斷方式。增加低血鉀診斷的正確率而減少相關併發症與死亡之發生是第一線醫療人員所必須熟悉的。

關鍵字

低血鉀（Hypokalemia） ； 心電圖（Electrocardiogram） ； 偽QT間期延長（Pseudo QT prolongation） ； QU間距（QU interval） ； 巨大U波（Giant U wave） ； ST段下降（ST segment depression）

並列摘要

Hypokalemia is an electrolyte imbalance that is easily neglected in clinical situations. Hypokalemia increases mortality in patients with arrhythmia, congestive heart failure, and acute myocardial infarction. A patient's symptoms, being unfamiliar with EKG patterns, and EKG patterns similar to other diseases may delay the diagnosis of severe hypokalemia (the official definition is ＜ 3.0 mEq/L or symptomatic). Lead II and V3 can present a typical EKG pattern in hypokalemia. When hypokalemia occurs, the T wave decreases first. When hypokalemia is exacerbated, other signs such as T wave inversion, a decrease of the ST segment, an increase of the PR interval and the p wave, an U wave or a giant U wave may occur. The typical EKG pattern in hypokalemia usually appears when the concentration of serum potassium is ＜ 2.7 mEq/L. The ST segment usually decreases in lead V1-V3, accompanied by a U wave, when hypokalemia becomes more severe. Pseudo QT prolongation should not be confused with actual QT or QU prolongation. Tachycardia and blood pressure are confounding factors for EKG in hypokalemia. Severe hypokalemia may increase the automaticity and reducing the conduction velocity of cardiac myocytes. Fatal arrhythmia may occur if severe hypokalemia is not treated immediately. Doctors may increase diagnosed sensitivity in EKG by using the height of the U wave, the amplitude of the ST depression, and the ratio of T/U. In people with cardiac hypertrophy, ischemic heart disease, or who are using anti-arrhythmia drugs, there are other ways to differentially diagnose increased sensitivity. As the clinical staff, it is our responsibility to increase diagnostic accuracy for patients with hypokalemia and decrease the rate of related complications and mortality.