2 Cases of Metabolic Disturbances: What the ECG Shows

December 31, 2006

A 43-year-old woman presents with a 1-week history of fatigue and weakness.She has also experienced vague abdominal discomfort and constipation for thepast month. She has no history of cardiac disorders.Which of the following metabolic disturbances does the ECG implicateas the most likely cause of the patient's symptoms?

Case 1:


Woman With Fatigue, Weakness, and GI Symptoms


A 43-year-old woman presents with a 1-week history of fatigue and weakness.She has also experienced vague abdominal discomfort and constipation for thepast month. She has no history of cardiac disorders.Which of the following metabolic disturbances does the ECG implicateas the most likely cause of the patient's symptoms?

A.

Hypokalemia.

B.

Hypercalcemia.

C.

Hyperkalemia.

D.

Hypocalcemia.

Case 1: Woman with fatigue, weakness, and GI symptoms.

The ECG tracingis pathognomonic for

hypercalcemia,

B.

It demonstrates a marked shorteningof the time between Q-wave onset and the beginning of the T wave. TheST segment and T wave have a normal morphology, but the ST segment is significantlyshortened, along with the overall corrected QT interval, which is330 milliseconds (normal range, 350 to 450 milliseconds). The T wave appearsto have been "pushed to the left," abutting the QRS complex.A diagnosis of primary hyperparathyroidism was made. The patient'sserum calcium level was 12.8 mg/dL (normal range, 8 to 10.4 mg/dL). Followingtreatment with intravenous fluids and diuretics, the serum calcium levelnormalized and the ECG changes resolved.The most common causes of hypercalcemia are hyperparathyroidism andmalignancy. Symptoms, which are frequently nonspecific, include fatigue, weakness,abdominal pain, constipation, and nephrolithiasis. Rarely, confusion anddelirium may occur, primarily if the hypercalcemia develops acutely.

Case 2:


Middle-aged Woman WithWeakness, Fatigue, and Dyspnea


A 65-year-old woman with chronicrenal disease presents with a 2-weekhistory of generalized muscle weakness,fatigue, and dyspnea.Based on the ECG tracing, whichmetabolic disturbance is the most likelycause of the patient's symptoms?

A.

Hypokalemia.

B.

Hypercalcemia.

C.

Hyperkalemia.

D.

Hypocalcemia.

Case 2: Middle-aged woman with weakness, fatigue, and dyspnea.

The ECGtracing demonstrates a prolonged QT interval but an entirely normal T-wavemorphology; this pattern is consistent with

hypocalcemia,

D.

Because the STsegment, rather than the T wave, is affected, the time interval from the Q waveto the onset of the T wave may be a more sensitive indicator of hypocalcemia.In contrast, hypokalemia and hypomagnesemia invariably result in abnormalT-wave morphology (usually flattening), whereas hyperkalemia often results inpeaked T waves.This patient had end-stage renal disease and a serum calcium level of6.3 mg/dL (normal range, 8 to 10.4 mg/dL). She was treated with oral calciumsupplements and vitamin D (calcitriol). Clinical manifestations of hypocalcemiaare often nonspecific; they include fatigue, hyperirritability, anxiety, and depression.Rarely, patients present with muscle weakness, seizures, and tetany.Common causes of hypocalcemia include hypoparathyroidism and end-stagerenal disease with concomitant vitamin D deficiency.