Frequently Asked Questions: Cardiotoxicity

The most common form of cardiotoxicity caused by chemotherapy consists of weakening of the muscle tissue that is responsible for the heart’s pumping function. This condition of reduced pumping strength of the heart is called cardiomyopathy. Cardiomyopathy can result in symptoms such as fatigue, reduced capacity to perform physical activities, shortness of breath with modest physical exertion and fluid retention. Together, these symptoms comprise a syndrome that doctors call “heart failure.”

Other forms of cardiotoxicity include:

• Inflammation of the sac that surrounds the heart (pericarditis), which can result in dangerous accumulation of fluid around the heart
• Impairment of the conduction of the electrical impulses among the four heart chambers, which can result in slowing of the heart beat and reduced pumping efficiency
• Blockage of the coronary arteries, which can lead to a heart attack
• Damage to the heart valves, which can lead to obstruction of blood flow across the valves or to backflow across the valves

Your oncologist and/or radiation oncologist will inform you of the potential for cardiotoxicity of any cancer treatment under consideration. He or she may refer you to a cardiologist with expertise in assessing and treating cancer patients at risk for heart damage.

Cardiotoxicity is diagnosed by a noninvasive ultrasound test called an echocardiogram. This test takes about 45 minutes, and provides detailed information concerning the strength of the heart muscle, function of the four heart valves, blood flow and blood pressure within the chambers of the heart.

Cancer of the left breast and lymphomas are the cancers most likely to require cardiotoxic treatments--chemotherapy and radiation therapy--to cure the cancer. If you have a pre-existing heart condition, whether it is a prior heart attack or coronary artery disease, cardiomyopathy, uncontrolled hypertension, heart valve dysfunction or an irregular heartbeat, you should have a thorough assessment by a cardiologist familiar with the cardiotoxicity of anticancer treatments and with the risks and benefits of treatment with a cardiotoxic agent.

Only a relatively limited number of cancer drugs have the potential for major adverse cardiac side effects. However, these include some of the most powerful and effective anticancer agents, such as doxorubicin (Adriamycin), trastuzumab (Herceptin) and cyclophosphamide (Cytoxan), which are used to treat a wide variety of cancers, including those of the breast, colon and blood.

Because these agents are so effective in treating the target cancer, the potential for cardiotoxicity is accepted as a risk worth taking. Furthermore, we now have a good understanding of the risk factors and doses that are associated with cardiotoxicity, and can modify risk factors as well as dosing regimens to minimize the likelihood of damage to the heart incurred as a result of potentially lifesaving chemotherapy.

Radiation therapy directed to the chest can cause heart damage when given in doses exceeding a certain threshold. However, to the extent possible, the heart is physically shielded from the radiation beam in order to minimize exposure of the heart.

Radiation therapy applied to the chest for cancer of the left breast or for certain cancers involving blood-forming cells (such as lymphoma) can also lead to cardiotoxicity. Radiation therapy for cancer involving the right breast but not the left breast does not cause cardiotoxicity.

Unfortunately, no. Many of the established cancer drugs kill cancer cells by interfering with the replication and metabolism of DNA. This means that any rapidly dividing cell type (such as blood-forming cells) might be susceptible to the cell-killing effect of the drug. Newer anticancer agents target specific biochemical reactions within cancer cells that are critical for the unregulated proliferation of the cancer cell. Unfortunately, in some cases the biochemical reactions that are responsible for cancer cell growth are also required for the normal functioning of heart muscle.

An example of a drug that targets such a reaction is trastuzumab (Herceptin), which is used to treat certain forms of breast cancer. When used as a single agent, it has a very low probability of causing cardiotoxicity. However, when administered as part of a multi-drug regimen that includes doxorubicin, the likelihood of cardiotoxicity can be as high as 28 percent.

Most forms of chemotherapy-induced cardiotoxicity appear within a year of treatment, but sometimes the first manifestation occurs many years after treatment is completed. This is particularly true for radiation-induced cardiac injury, which has been known to appear as many as 20 years after exposure to chest radiation.

In general, the higher the cumulative dose of cardiotoxic chemotherapy or radiation therapy, the more likely it is that cardiotoxicity will ensue. This means that for some patients receiving anticancer treatments exceeding certain threshold doses, doctors recommend lifelong cardiac monitoring.