LOW POTASSIUM: THE FORGOTTEN FACTOR IN SUDDEN CARDIAC DEATH
I needed to revisit my studies on potassium, heart health and electrolytes just before Christmas when my husband suffered a low-potassium induced cardiac arrest. Fortunately, he survived as he was in A and E at the time, which is the best place to have a cardiac arrest if you are going to have one! A year earlier, he suffered a single catastrophic blood clot in the main artery to the small intestine. Since that time, his nutrition, including electrolyte balance, has been severely compromised. This Newsletter covers why potassium should be closely monitored in all cardiac patients.
The heart is an electrical organ
As the name suggests, electrolytes are minerals that are capable of conducting electricity and therefore play a vital role in the health of the heart. Examples of electrolytes are sodium, potassium, chloride, calcium, magnesium and phosphate. The electrical conduction system of the heart receives electrical signals that cause the chambers of the heart to contract. Right after the heart contracts, it needs to relax. These electrical activities of the heart are what is captured on an ECG reading, a basic test that your GP or cardiologist runs to determine if you are having heart rhythm problems.
Low potassium induced sudden cardiac death
According to the British Heart Foundation, someone dies from sudden cardiac death in the UK every 8 minutes. The traditional concept of why this occurs is the ischaemic heart disease model i.e. when the heart is starved of oxygen due to lack of blood flow to the coronary arteries. Less well known is that a substantial number of sudden cardiac deaths occur because of low potassium in the blood (hypokalaemia).
Potassium Regulation
Long-term potassium regulation in the body depends upon excretion of potassium from the kidneys. However, short-term regulation (seconds to minutes) depends upon several different body tissues. The largest single pool of potassium reserves is in the skeletal muscles. This is approximately 225 times higher than the total potassium content in the blood. The intricate mechanism of the body’s sodium/potassium pumps can shift potassium from the blood to storage muscles, causing low blood (serum) potassium within seconds to minutes!
LOW POTASSIUM AND SUDDEN DEATH
Why is this significant? When potassium moves from blood to muscle stores, the serum potassium level drops. The standard hospital range for potassium in blood serum (the fluid part of the blood) is from 3.5 to 5.0 millimoles per litre (mmol/L). The balance between potassium in the serum and the muscles is key. Potassium needs to be kept within a strict range for optimal beating of the heart. When serum potassium drops too low (or rises too high) this can trigger serious disruption to heart rhythms (ventricular tachycardia) which can lead to sudden cardiac death. In this Newsletter, I will focus on low potassium.
Optimal potassium in cardiac patients
The MacDonald and Struthers (2004) scientific paper What is the optimal serum potassium level in cardiovascular patients? states that the more at risk of fatal arrhythmia and sudden cardiac death a patient is, the more attention should be given to potassium regulation. It points to the increasing evidence that the serum potassium level should be maintained above 4.5 mmol/L in heart failure patients. Therefore, rather than following the standard hospital potassium reference range of 3.5 -5.0, the advice is that serum potassium levels should be maintained between 4.5 - 5.0 in the cardiac risk patient.
Potassium and Magnesium
As most cardiologists know, the ability to successfully correct low potassium levels depends upon the successful reversal of low magnesium. Magnesium and potassium work together to get optimal balance between serum and muscle stores. You need magnesium on board to get potassium into the cells; you need potassium to get magnesium into cells. Low magnesium can trigger low potassium. Therefore, the ability to correct low potassium mandates the simultaneous reversal of low magnesium. So, the message is - don’t forget magnesium when supplementing potassium! Correction of low potassium will prove difficult unless magnesium is first replaced. Both are common in critically ill patients.
Potassium and the QTc interval
On an ECG is a measurement known as the QTc interval. This is used to assess the electrical performance of the heart. It is calculated from the start of the Q wave to the end of the T wave, and reflects the time taken from when the cardiac ventricles (large chambers at the bottom of the heart) start to contract to when they finish firing. QTc prolongation occurs when the heart muscle takes longer to contract and relax than usual. This can result in dangerous heart rhythms that lead to sudden cardiac arrest.
The Kallergis et al., (2012) paper Mechanisms, Risk factors, and Management of Acquired Long QT Syndrome: A Comprehensive Review states that both low potassium and severely low magnesium are risk factors for QTc prolongation and cardiac rhythm disorders and recommends correction of potassium to the high normal range to shorten the QTc interval and reduce the incidence of associated sudden cardiac death. So, the QTc interval can act as an indirect monitor of potassium and magnesium status.
Potassium, magnesium and stress
What happens to electrolytes under severe stress? In the paper A dyshomeostasis of electrolytes and trace elements in acute stressor states; impact on the heart, the authors Whitted et al.,2010 state that stress can rapidly deplete potassium, magnesium and other electrolytes. The resulting altered electrical behaviour with prolonged QTc interval, increases vulnerability to heart rhythm problems like atrial fibrillation and ventricular tachycardia. Then, the critical balance between the pro oxidant and antioxidant defences of the body influences whether heart cells will survive or die and get replaced by fibrous scar tissue compromising the muscular efficiency of the heart.
Potassium and Diet
The hormone insulin promotes a shift of potassium from blood to muscle stores, predisposing towards low serum potassium. What triggers insulin secretion and spikes? High-refined carbohydrate meals! What if you eat a hyper-refined diet? Could a meal of pasta, following by dessert, coke and coffee trigger a few moments of potentially catastrophically low serum potassium? You bet! No matter how much you eat, or whatever else is going on in your gut, if you have meal that induces an insulin spike, it is going to start shifting potassium from your blood to your muscles. That is why studies find a correlation between low potassium and diabetes type 2.
Potassium and The Dark Side of Fasting
Friedli et al. (2017) in the paper Revisiting the referring syndrome; Results of a systematic review outline what happens to the serum potassium level after having a refined carbohydrate meal after a period of starvation. Remember that insulin is secreted after high carb intake? The term ‘Refeeding Syndrome’ was coined at the end of World War 2 after an unexpectedly high mortality rate was observed in prisoners who had been freed by the Allies from the Nazi concentration camps. After a long period of starvation and malnutrition, soldiers hasted to feed the starving prisoners, mostly with what they had in their pockets - K rations and chocolate. Disaster struck with many dropping dead of dehydration and heart attacks. The reason - after such a starved and catabolic state, glucose concentration and insulin secretion rose suddenly, leading to an overwhelming shift in electrolytes, low serum potassium and cardiac arrest.
Can we see that in a modified form in some of our elderly population? Many of our elderly don’t bother to eat properly. Can a person who hasn’t eaten for about 10 hours, get a catastrophic sudden insulin spike followed by low potassium, then suffer a cardiac arrest? Absolutely!
The same can be seen with intermittent fasting, which has become increasingly popular. The message here is that intermittent fasting only works safely with healthy food. If you’re going to fast, don’t eat highly-processed sugary crap!
Potassium and excessive exercise
In his paper Hormonal and pharmacological modification of plasma potassium homeostasis, Clausen (2010) outlines the potential risk of sudden cardiac death associated with excessive exercise. The risk was seven times higher in those who rarely engaged in physical exercise. The game of squash has been studies in the medical literature following a high incidence of ventricular arrhythmias and sudden death after the game. Struthers et al., (1988) suggest that this may be related to the following sequence of events - excessive exercise triggers muscle destruction - triggers release of stored potassium in muscle - triggers excess potassium - triggers rebound low potassium - triggers cardiac arrest. Another study on 21 squash players showed two thirds had arrhythmia on their ECG tests immediately after the game.
Cooking up a perfect cardiac storm
To sum up, here is a recipe of ingredients that can cook up the perfect cardiac storm leading to altered heart rhythms and sudden cardiac death:
Baseline potassium below 4.0 (despite the hospital standard reference range).
Baseline magnesium below 2.0 (keep in mind the 4:2 potassium: magnesium ratio for cardiac health).
Prolonged QTc interval (>460) - indicates the need for potassium and magnesium supplementation.
Sarcopenia (loss of muscle mass) - depletion/dysregulation of potassium stores.
Psychological stress
Diet-induced changes in insulin metabolism (high refined carb diet).
Some pharmaceuticals i.e. some diuretics that deplete the body of potassium.
Excessive exercise
Recipe for optimising potassium
Serum potassium 4.5-5.00 in cardiac patients. Speak to your consultant to arrange regular potassium blood tests.
Serum magnesium at least 2.0 ng/dl. Red Cell magnesium is a better marker for potassium status than serum magnesium.
Monitor QTc interval (can get economical ECG monitoring devices online). If above 460, indicates need for potassium.
Monitor first morning urine - if pH is below 6.4, indicates need for potassium and magnesium.
Monitor symptoms - muscle cramps can indicate both potassium and magnesium deficiencies, confusion/ slurring of speech in the elderly can reflect low potassium and magnesium.
Check you are not taking pharmaceutical drugs which deplete your body of potassium and other electrolytes like sodium. Speak to your prescribing doctor about this.
Pin prick home electrolyte monitors (however, these can be rather expensive). There is a need for the development of a home potassium measuring device for cardiac patients, similar to glucose monitors for diabetics.
Don’t eat high sugar, refined carbohydrate crap!
Electrolyte supplementation - ideally this should be monitored by a qualified health professional. Oral potassium is safe when well monitored as the body knows what to with it, in contrast to intravenous potassium which is only delivered in hospital settings.
Potassium bicarbonate and citrate are considered safe and effective. Avoid potassium chloride.
Don’t forget the magnesium! There are different types - glycinate, malate, threonate, citrate. Avoid magnesium oxide which is unabsorbable and will give you diarrhoea.
If you would like help with any chronic issues, please get in touch with the Good Health Clinic on goodhealthclinic@outlook.com to request a free 30 minute Enquiry Call or book an appointment. Please note that an Enquiry Call is not a consultation but an exploratory call to see if this a clinical approach you wish to pursue.
Disclaimer:
All advice given out by Suzanne Jeffery and the Good Health Clinic is for general guidance and informational purposes only. All advice relating to other health professionals’ advice is for general guidance and information purposes only. Readers are encouraged to confirm the information provided with other sources. Patients and consumers should review the information carefully with their professional health care provider. The information is not intended to replace medical advice offered by other practitioners and physicians. Suzanne Jeffery and the Good Health Clinic will not be liable for any direct, indirect, consequential, special, exemplary or other damages arising therefrom.