Which of the following describes the marked ECG finding?

Notice the low voltage ECG which is defined as amplitude of all qRS complexes in limb leads less than 5 mm. Also notice that amplitude of qRS complexes is variable in all the arrow marked leads. Hence, the ECG is diagnostic of electrical alternans. The triad of sinus tachycardia with low voltage ECG and electrical alternans is highly suggestive of pericardial effusion.