Examining the Link Between Heart and Kidney Disease

Illustration of male kidneys and heart

To one extent or another, all the body’s organs are interdependent—the normal functioning of one organ relies to at least some degree on the normal functioning of all the others. This interdependency is particularly striking between the heart and the kidneys.

It is distressingly common for people with significant heart disease to eventually develop chronic kidney disease. It is also common for people with kidney disease to develop heart disease. This means that people who have a problem with one of these organ systems must be alert (along with their doctors) to the possibility of developing a problem with the other, and to take reasonable steps to lower the risk of this happening.

The Relationship Between Heart Disease and Kidney Disease

Heart disease and kidney disease often go together. Experts have defined at least five ways in which cardiac disease and renal disease are interrelated:

So, if either the heart or the kidneys are affected by some form of the disease, there is a relatively high risk that the other organ will develop medical problems. This general relationship between them has sometimes been called the cardiorenal syndrome.

It should not be surprising that having the disease in both of these organ systems is worse than having the disease in just one. People with chronic heart failure who also have kidney disease are at a substantially higher risk of early death. And among people with chronic kidney disease, cardiovascular problems end up causing death in almost half.

Although the many ways in which heart disease can lead to kidney disease, and vice versa, are not yet completely understood, in recent years our understanding of this relationship has advanced greatly, helping us develop reasonable steps to lower the risk of this happening.

Heart Disease Can Cause Kidney Problems

Heart failure is a clinical condition that can result from almost any form of heart disease. In general, when heart disease produces kidney disease, heart failure is already present. There are several ways in which heart failure can lead to kidney disease. The main ones are:

Drop in cardiac output. In chronic heart failure, the amount of blood being pumped by the heart can be reduced. This can lead to a reduction in the volume of blood being filtered by the kidneys, which causes renal function to deteriorate.

Neurohumoral changes. To compensate for the drop in cardiac output that often occurs in heart failure, a number of changes occur in the sympathetic nervous system and in the hormones that control the volume of salt and water in the circulation—that is, in the renin-angiotensin-aldosterone system.

These changes lead to increased salt and water retention, which in the short term can improve the amount of blood reaching vital organs. However, in the long term, these neurohumoral changes lead to edema (swelling) and to even further reductions in the cardiac output. So, chronically, these changes reduce blood flow to the kidneys, and kidney function suffers.

Increased pressure in the renal veins. In heart failure, reduced cardiac efficiency increases the pressure within the veins. Higher pressure in the renal veins (the veins that drain the kidneys) makes it more difficult for the kidneys to filter blood. Again, renal function gets worse.

As a result of these and other mechanisms, chronic heart failure places several stresses on the kidneys that prevent their normal functioning, and that, over time, can cause permanent damage to the kidneys.

How Kidney Disease Causes Heart Problems

On the other hand, kidney disease often leads to cardiac problems. It does this in two major ways.

First, chronic kidney disease commonly produces salt and water retention, which can place significant strain on the heart. If any degree of underlying heart disease is present, whether it is CAD, heart valve disease or cardiomyopathy (heart muscle disease), this increase in the body’s fluid volume can cause cardiac function to deteriorate and can lead to overt heart failure.

Second, chronic kidney disease is a major risk factor for developing CAD, and for worsening any underlying CAD that might be present. People with chronic kidney disease who also have CAD tend to have significantly worse symptoms, and worse outcomes, than people who have CAD without kidney disease.

Chronic Kidney Disease Often Leads to CAD

There are two reasons people with chronic kidney disease have a high risk of developing CAD.

For one thing, population studies have shown that people with chronic kidney disease tend to have a high incidence of typical risk factors for CAD. These include smoking, diabetes, high cholesterolhypertension, sedentary lifestyle, and older age.

In addition, chronic kidney disease itself greatly increases the risk of CAD. Kidney disease increases this risk by several mechanisms. For instance, the toxins that accumulate in the blood because of abnormal kidney function (the so-called uremic toxins) increase the risk for CAD. Other blood and metabolic abnormalities associated with chronic kidney disease also increase the risk. These include abnormal calcium metabolism, anemia, a chronic inflammatory state (with elevated CRP levels), poor nutrition, and elevated blood protein levels.

Taken together, these factors appear to produce generalized endothelial dysfunction, a condition associated with CAD and other cardiovascular conditions including hypertension, diastolic dysfunction, and cardiac syndrome x.

How to Prevent Diseases in Both Organs

Because heart disease and kidney disease go together so frequently, anyone who has a problem with one of these organ systems should work with their doctors to prevent disease from occurring in the other.

Heart disease. If you have a cardiac diagnosis, the best way to avoid developing kidney disease is to make sure you are receiving all the appropriate therapy for your heart condition. This means not only getting all the treatment you need for the underlying heart condition itself (whether it’s CAD, heart valve disease, cardiomyopathy, or any other condition), but also doing everything you can to achieve and maintain the optimal health of your cardiovascular system in general. This means aggressively treating hypertension, diabetes, and elevated lipids, maintaining a healthy weight, not smoking, and getting plenty of exercise.

Kidney disease. As we have seen, kidney disease itself is now considered a major risk factor for developing CAD. This means that if you have kidney disease, it becomes critically important to get control of all your other cardiovascular risk factors (which we have just mentioned). Aggressive risk factor management should become a chief focus for you, and you should take whatever steps are necessary to optimize your risk.

In addition, most experts recommend that anyone with chronic kidney disease should be placed on a statin drug, and that serious consideration should be given to prophylactic aspirin. These measures can help to prevent the more serious consequences of CAD.

The Bottom Line

Having kidney disease can greatly increase the risk of developing serious heart disease, and vice versa. Anyone with a medical issue involving either of these organ systems needs to take every measure available not only to optimize therapy for the existing diagnosis, but to prevent the development of a new medical problem in another vital organ.

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