Kidney disease is both a cause and a consequence of heart disease, the number one global killer.

Chronic kidney disease is common, affecting 9 per cent to 13 per cent of the general adult population, and these figures are on the rise.

Cardiovascular disease is quite prevalent in people with CKD regardless of age, stage of kidney disease, or if they had a kidney transplant.

It is estimated that 25 to 70 per cent of patients with kidney disease have concomitant heart condition(s). This association strengthens more as the kidney (or renal) function declines, placing patients with kidney disease at the “highest cardiovascular risk” level, according to the recommendations of the National Kidney Foundation task force on cardiovascular disease in chronic renal disease. In fact:

• Most patients with renal failure do not die from their kidney disease, but from a cardiovascular problem.

• Having CKD amplifies the risk of death from cardiovascular disease, whether or not other risk factors for heart disease are present.

• Even early or mild CKD places a person at higher risk of heart attacks, other heart ailments and cardiac death.

• Death from cardiovascular disease is 20 times more likely in kidney dialysis patients than in the general population.

• While high blood pressure and diabetes are major risk factors for both kidney and heart diseases, the development of CKD in persons with either diabetes or hypertension, or both, further increases their risk of developing cardiovascular conditions.

How CKD causes heart disease remains largely unknown, as 60 per cent of major cardiac disease trials have excluded patients with kidney insufficiency.

The following are complications that develop from renal disease and can lead to cardiovascular pathology:

• Anaemia. When your body does not have enough red blood cells the kidneys manufacture a hormone called erythropoietin, which drives the bone marrow to make more. If your kidneys are damaged, your erythropoietin level can fall and your marrow will not make enough red blood cells. Fewer red blood cells mean less oxygen going to the different tissues and organs, including the coronary vessels, and a person may be susceptible to a heart attack.

• High renin levels. The kidneys make renin, which is an enzyme that helps to control blood pressure. Damaged kidneys may release too much renin, which can lead to hypertension. The latter may increase the risk for a heart attack, congestive heart failure, and strokes.

• High homocysteine levels. Damaged kidneys cannot remove extra homocysteine, an amino acid in the blood. High levels of homocysteine can lead to coronary and cerebrovascular diseases.

• Calcium-phosphate levels. Damaged kidneys cannot keep calcium and phosphorus levels in balance. Often, there is too much phosphorus and calcium in the blood. When this happens, there is a risk for coronary plaque (or blockage) build-up.

• Decreased salt and fluid elimination. The kidneys are responsible for the elimination of excess fluid and sodium. When damaged, they will cause fluid and salt retention, overtaxing the heart and vessels and, again, causing high blood pressure, accelerated atherosclerosis, cardiac pump failure, and stroke.

Conversely, how heart disease leads to kidney failure is not very clear but the following mechanisms are likely:

• Vascular disease, in general related to smoking, high cholesterol, diabetes and hypertension, can also involve the renal vessels leading to kidney shrinkage and functional decline.

• A weak cardiac muscle, in the setting of congestive heart failure, would not pump enough blood to the kidneys leading to progressive renal insufficiency.

• Some medications used to treat the heart could unmask or accelerate kidney issues.

In many patients, the above interplay between the two organs is quite complicated, setting the stage for a vicious cycle of negative feedbacks where one organ’s decline harms further the other and vice versa, often leading to a multi-organ damaging situation, referred to as “cardio-renal syndrome”.

However, trials have conclusively shown that early detection and aggressive treatment of cardiac and kidney diseases along with tight control of their risk factors may markedly slow the progression of both conditions.

• Joe Yammine is a cardiologist at Bermuda Hospitals Board. He trained at the State University of New York, Brown University and Brigham and Women’s Hospital. He holds five American Board certifications. He was in academic practice between 2007 and 2014, when he joined BHB. During his career in the US, he was awarded multiple teaching and patients’ care recognition awards. The information herein is not intended as medical advice nor as a substitute for professional medical opinion. Always seek the advice of your physician. You should never delay seeking medical advice, disregard medical advice or discontinue treatment because of any information in this article.