Hyperkalæmia

Report:

Supraventricular tachycardia, probably sinus, 128/min

Right bundle branch block

Left anterior hemiblock

Tall T waves suggest hyperkalæmia

Comment:

Hyperkalæmia diminishes the amplitude of P waves; they eventually disappear altogether, with atrial paralysis. The sinus node continues beating (yes, beating!)90 and its impulses reach the AV node via internodal tracts, more resistant to potassium than the surrounding atrial muscle. This invisible sinus rhythm is called sinoventricular conduction. Its presence here cannot be proven or disproven, as is often the case in hyperkalæmia. The rhythm may just as well be a junctional one – a non-paroxysmal junctional tachycardia (NPJT). It could also be a fascicular VT.

The peak measured potassium was 7.5 mEq/L. As it fell, the P waves reappeared and the ventricular conduction normalised (Fig 121a below, 90 minutes later). Hyperkalæmia usually prolongs the QRS complex in a diffuse, nonspecific manner, but can, as in this case, produce a classic fascicular block.