Hyperkalemia

Tall peaked T waves with a shortened QT interval are usually the first findings

Progressive lengthening of the PR interval and QRS duration

P wave may disappear, and ultimately the QRS widens further to a sine wave pattern

Ventricular standstill with a flat line on the ECG ensues with complete absence of electrical activity.

Beta blockers interfere with the beta-2-adrenergic facilitation of potassium uptake by the cells, particularly after a potassium load. An increase in serum potassium is primarily seen with nonselective beta blockers (such as propranolol and labetalol). In contrast, beta-1-selective blockers such as atenolol have little effect on serum potassium since beta-2 receptor activity remains intact