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Objective: To demonstrate whether ECG changes induced by hyperkalemia correspond with previously described changes.

Design: Prospective

Animals: Eighteen dogs and 22 cats with serum potassium levels >5.5 mEq/L as the result of various disease processes.

Procedure: Once hyperkalemia was documented, the following data were collected: ECG (n=40), total magnesium (mg/dl) (n=18), total calcium (mg/dl) (n=31), and venous blood gas (n=20). Animals were divided into 5 groups based on expected ECG's changes associated with hyperkalemia (mEq/L): Group 1- 5.5–6.5; Group 2- 6.6–7.0; Group 3- 7.1–8.5; Group 4- 8.6–10.0; Group 5- >10.0. ECG's were interpreted to determine if the rate, rhythm and changes in the P-QRS-T complex were similar to those previously reported.

Results: Twelve ECGs demonstrated changes previously described, while 28 did not: Group 1 (n=7)- 1/7; Group 2 (n=2)- 0/2; Group 3 (n=14)- 4/14; Group 4 (n=6)- 3/6; Group 5 (n=11)- 4/11. Many ECG abnormalities not previously described were also identified such as atrioventricular dissociation and ventricular tachyarrhythmias. Blood gas analysis revealed acidemia (19/20) with severe acidemia (pH<7.2) in the majority (16/19). Hypocalcemia was documented (5/13) and most of these patents (4/5) were in Group 5. Hypermagnesemia was documented in the majority of patients (10/18), though not in one particular group.

Clinical Implications: It is difficult to establish typical ECG changes in patients with hyperkalemia, which represents a departure from the historical description. Hypocalcemia may be involved with ECG changes and arrhythmias in Group 5. Hypermagnesemia causes electrocardiographic abnormalities similar to those described with hyperkalemia and therefore does not explain the results of this study. There likely are complex interactions with electrolytes and acid base abnormalities that affect ECG formation.