Dr.S.Venkatesan MD

Human physiology can dramatically surprise us.Here is a situation regarding K+ ion and cardiac function.

Low potassium level is a well known cause for skeletal muscle  weakness and paralysis.While,in cardiac muscle usually the opposite happens.It is the high potassium levels that depresses and cause paralysis.(That’s why,it is used in cardioplegic solutions. )

But,the classical differences between skeletal and cardiac muscle need not apply in critically  low levels of K +

What happens when K + is critically low ?

We know, K + is the vital  ion that maintain not only the membrane potential ,(Recall Nernst potential ) but also keeps the action potential floating and dipping with every beat.

Imagine the intracellular chaos when these ion levels changes in dramatic fashion . (Of course,God has ensured very tight regulatory controls at various levels within each cell ! )

However , ECG changes are expected 100 % of time with falling K +  especially below 3meq.Surprisingly , low K + levels have little  mechanical impact.(Or is it our ignorance,considering the fact , cardiac electrical mechanical activities are tightly coupled?)We have to find answer from patients like this .

A  30 year old women came with breathlessness and fatigue and her ECG.

Can we afford to miss a diagnosis of STEMI ? With all our collective wisdom STEMI was diagnosed promptly . . . of course wrongly !

She was adviced  streptokinase.A shrewd fellow who reviewed  the old records spotted the past  history  hypokalemia , and Inj streptokinase was put on hold.(Lucky patient  . . . she was not shifted to cath lab )

Her  K + was 2.3 Meq. The LV function was significantly impaired with global hypokinesia, which  improved with correction of K+.

She was later referred for  nephrology work up , they had made a possible renal tubular disorder for the Hypokalemia.

Clinical Implication.

When potassium levels are critically low myocardial  function may deteriorate.Here is a patient with dramatic STEMI like ECG with extreme hypokalemia.

Our ignorance regarding electrolytes and myocardial function  remains unexposed .In critical care units  wide swinging metabolic and electrolytic  parameters are common.ECG is just a marker  for these .Similarly all LV dysfunctions are not primary myocardial disorders (Sepsis, Hypoxia, Extreme acidois , Uremia ,drugs,toxin  can lead to myocardial dysfunction.)

Experienced  physicians  do not form hurried opinion.Wait . . . allow things to settle down and assess again.After all ,there is long list of causes for ST elevation other than STEMI !

Reference