Certain drugs used in Chemotherapy have serious side effects on the patient’s heart. These effects are collectively referred to as Cardiac Toxicity. As a result of this disorder, the patient’s heart is unable to pump enough blood to meet the body’s requirements of essential oxygen and nutrients. The most well-known cause of this disorder in cancer patients occurs a result of the treatment with a class of drugs known as Anthracyclines.
Cardiac Toxicity
Cardiac toxicity occurs when the heart muscles are damaged by a toxin. It may result in Arrhythmias ( abnormal changes in the heart rhythm) or it can lead to the weakening of the heart’s pumping action.
Causes
- Radiation applied to the chest and a few drugs used in Chemotherapy may result in Cardiac toxicity in cancer patients.
- Doxorubicin (Adriamycin®), a frequently prescribed drug – Anthracycline. is a well known cause of cardiac toxicity. Anthracyclines also include the following drugs: Liposomal doxorubicin, Idarubicin, Daunorubicin, Epirubicin, and Mitoxantrone. These are mainly used to treat Leukemia, Lymphoma, Multiple Myeloma and Breast Cancer.
These drugs are intercalating agents that inhibit DNA and cellular replication, a fundamental process in cancer progression. Unable to replicate, these cancer cells eventually die by a process known as ‘Apoptosis’. Anthracyclines are also known to enhance the production of free radicals and since free radicals are not easily detoxified by cardiac tissues, this has been implied as the cause of the cardiac disorder that results from Anthracylcines.
Symptoms of Cardiac Toxicity
- Fatigue
- Shortness of breath on exertion
- Discomfort while lying on ones back
- Swelling of the ankles and weight gain
Diagnosis
The following examinations and tests are usually carried out for the diagnosis of Cardiac Toxicity:
- Chest X-ray: An enlargement of the heart seen on a chest x-ray may indicate that the heart muscle was damaged
- Electrocardiogram (ECG): Irregularities in an ECG test record may indicate occurrence of Arrhythmias
- Heart Sounds: The doctor listens for abnormal heart sounds with a stethoscope. An additional sound other than the normal sound, referred to as a ‘murmur’, may indicate possible damage to the heart.
- Echocardiogram: It shows up if there is any irregularity in the filling up of blood in the heart and pumping to the rest of the body.
- Multi Gated Acquisition (MUGA) Scan: In this procedure, a radioactive substance is injected into a vein and specialized images of the heart are taken. The entire activity of the heart can be visualized from these images.
Prevention of Cardiac Toxicity
Method of administration
The method of drug administration also has an effect on the risk of cardiac toxicity. Rapid administration of drugs results in high blood levels, which may cause more heart damage than the same amount of drug given over a longer period of time. Administration of smaller doses more frequently may also reduce the toxicity when compared to large doses of drugs at longer intervals.
Liposomal Anthracyclines: The risk of heart problems is considerably lower with Liposomal formulations than with conventional Anthracyclines. Liposomal Anthracyclines are Anthracyclines encapsulated in a Liposome (a tiny globule of fat). Due to this, it remains in the body for some time as the immune system doesn’t target it for elimination and it is not broken down quickly by the liver.
Dexrazoxane (Zinecard®): This drug has been shown to reduce the severity of damage caused by Doxorubicin. It protects the heart muscles by blocking the formation of oxygen free radicals, which are the main cause of cell damage.
Treatment
Initial treatment of Cardiac Toxicity is done by stopping or reducing the dosage of the medication that is causing damage to the heart muscles. In later stages, this disorder is treated the same as any other case of heart failure.
- Diuretics: Damage to the heart may cause the patient to retain excess water and will lead to the swelling of their ankles. Diuretics like Furosemide (Lasix®) are prescribed to increase the amount of water excreted in the urine.
- Digitalis Drugs: Digitalis, like Digoxin (Lanoxin®), makes the heart beat more efficiently and also increases the amount of blood that is pumped to the rest of the body.
- ACE Inhibitors: These drugs improve blood flow to kidneys and the rest of the body by opening the arteries and lowering the blood pressure.
- Beta-Blockers: These medications are used if the patient has experienced a myocardial infarction (heart attack.)
