The Emerging Role of Cardio-Oncology

Patients diagnosed with cancer are most often bound to receive chemotherapy and/or radiation therapy, which can cause severe damage to the heart and blood vessels. Likewise, cancer treatments can worsen a preexisting cardiovascular condition, accelerating its progression and aggravating its prognosis.

As early diagnosis and new cancer therapies have significantly extended the life expectance of cancer patients, an increasing number of people are now surviving their malignancies long enough to face the risk of cardiovascular disease.

Clinical vigilance and cardiac monitoring carried out before, during, and after the administration of chemotherapy plays a central role in limiting the development of cardiovascular complications.

The doctor supposed to look after the heart of cancer patients is called a cardio-oncologist.

This article will focus on providing answers to common questions regarding the role of cardio-oncology, and explaining how the practice of cardio-oncology can improve the medical care of cancer patients.

1. What is cardio-oncology?

Cardio-oncology is a new cardiology sub-specialty, whose primary goal is to prevent and treat cardiovascular complications of cancer, chemotherapy, and/or radiation therapy.

2. What are the specific training requirements to become a cardio-oncologist?

A growing number of academic institutions in the USA have established a cardio-oncology fellowship program, adding cardio-oncology to the other cardiology subspecialties. The cardio-oncology training usually starts after completion of a general cardiology fellowship and usually lasts one year. 

3. What is the most common manifestation of cardiac toxicity in cancer-treated patients?

The most common cardiovascular complications in cancer-treated patients depend on the type of chemotherapeutic agent used, which in turn depends on the type of cancers, which are the most common in the population. Leaving aside prostate cancer, which is the most frequent cancer in man, but is seldom treated by chemotherapy, the most common cancer among women is breast cancer, and the second most common cancer for both genders is lung cancer. Doxorubicin and trastuzumab are commonly used for the treatment of breast cancer; while tyrosine kinase inhibitors are often used for lung cancer. Since the most common complication of doxorubicin, trastuzumab, and tyrosine kinase inhibitors is a weakening of the heart function, leading to heart failure, such complication is thus the most common manifestation of cardiac toxicity, for which cardio-oncologists are consulted. Left ventricular heart failure caused by cancer therapy, also known as "cancer therapy-related cardiac dysfunction" (CTRCD) affects approximately 10% of patients undergoing chemotherapy.

4. Are there other manifestations of cardiac toxicity in cancer-treated patients, beyond heart failure?

Cancer-related cardiac toxicity is not just "cancer therapy-related cardiac dysfunction". Actually, the adverse effects of cancer, chemotherapy, and/or radiation therapy on the heart and blood vessels are quite broad and comprise blood pressure fluctuations, cardiac ischemia (which occurs when areas of the heart do not receive adequate amounts of blood and oxygen due to the presence of blockages in the coronary arteries), thromboembolism (such as the formation of blood clots in arteries and veins), cardiomyopathy (a condition affecting the pumping function and/or the relaxation of the heart), arrhythmias (namely abnormal rhythms of the heart, either fast or slow), valvular heart disease (affecting the valves enabling the communication between the heart chambers), pericardial disease (such as thickening of the sack surrounding the heart) and early occurrence of atherosclerosis (the pathological process leading to blockage of the coronary arteries).

5. Can cancer itself cause cardiovascular complications?

Cancer increases considerably the risk of blood clot formation. The most common cardiovascular complications triggered by cancer per se are venous thrombosis and thromboembolism. Both conditions commonly start with the formation of a blood clot in a deep vein of the legs. However, only in the case of thromboembolism, a fragment of the main clot detaches and travels to the lungs, causing a severe complication called pulmonary embolism. Venous thrombosis and thromboembolism occur in 5% to 7% of patients with malignancy, an incidence that is much greater than that observed in the general population (approximately 0.1%). Patients with cancer constitute nearly 20% of all cases of thrombosis. Approximately 10% of all noncancer patients with venous thrombosis or thromboembolism will be diagnosed with cancer within 2 years.

6. What is the most common test used to diagnose and monitor left ventricular heart failure caused by cancer therapy or CTRCD?

The diagnosis of left ventricular heart failure caused by cancer therapy is based on the evaluation of cardiac function by serial monitoring of left ventricular ejection fraction. Every heartbeat consists of a repetition of two distinct cardiac phases: relaxation of the heart muscle with filling of the heart chambers and contraction of the heart muscle with ejection of the blood into the major vessels. The first phase of relaxation and filling is called “diastole”, while the second phase of contraction and ejection is called “systole”. In normal individuals, with every contraction, the heart ejects approximately 55-65% of the blood received during the preceding filling. This percentage is called left ventricular ejection fraction (LVEF), which represents the most accurate and reliable measure of cardiac function.

A drop in ejection fraction of 10% or more in cancer patients receiving chemotherapy toxic to the heart is the criterion followed by cardiac oncologists to diagnose cancer therapy-related cardiac dysfunction. Although historically the test utilized to diagnose and monitor cardiac function was a nuclear test called MUGA scan (using radioactive agents to label red blood cells), echocardiography (that is an ultrasound of the heart) has recently replaced MUGA scan because of some advantages, including widespread accessibility and availability, lack of radiation exposure or use of radioactive agents, as well as ability to provide information, going beyond left ventricular function, such as the function of the right ventricle and the cardiac valves. An emerging test useful to assess cardiac function is cardiac MRI. Although powerful, the broad diffusion of cardiac MRI is currently limited by its prohibitive costs.

7. Is it possible to reduce the severity or prevent the development of cardiac toxicity?

The risk of left ventricular heart failure in cancer-treated patients can be significantly reduced. The key to the prevention of cardiac toxicity is a standardized and systematic risk assessment. During this evaluation, the cardiac oncologist has two responsibilities: first, the estimation of the risk posed on the heart by the chemotherapeutic agent; second, the identification of the preexisting medical conditions increasing the patient’s risk to develop cardiac toxicity. Advanced age, elevated blood pressure (hypertension), blockages to the coronary arteries causing cardiac ischemia, heart failure, dysfunction of the heart valves, and previous need for chemotherapy toxic to the heart represents the most common conditions increasing the risk of developing chemotherapy-induced cardiac complications. Once the overall cardiovascular risk has been calculated, it has to be weighed against the potential oncological benefit. In this way, it is possible to individualize the best oncological therapy for the patient, balanced against the least cardiovascular risks. In patients developing left ventricular heart failure despite the preventive measures, which may include the initiation of protective heart medications, the role of the cardiac oncologist is to promptly inform the oncology team about the ongoing cardiac complication. Chemotherapy can be temporarily held or even discontinued, to be replaced with other chemotherapeutic agents, less toxic to the heart.