Electrocardiogram — Heart Rhythm Test in Cancer

An electrocardiogram is a routine clinical procedure that translates the heart's natural electrical impulses into graphical wave patterns on paper or a digital screen. Small adhesive sensor pads, known as electrodes, are attached to designated locations across the patient's chest, arms, and legs. These sensors detect tiny electrical currents generated by each heartbeat and send the data to a recording machine.

In oncology, the test provides crucial information regarding heart rhythm, rate, and the condition of cardiac muscle tissue. It allows clinicians to identify underlying arrhythmias, detect silent ischaemia, and measure the QT interval—the time it takes for the heart ventricles to contract and recharge. Because certain antineoplastic therapies can influence cardiac conduction, having serial ECG readings enables oncology teams to detect and address treatment-related changes before they progress to serious cardiovascular complications.

Cardiovascular health and cancer therapy are closely linked, giving rise to the specialised field of cardio-oncology. Many modern cancer medicines, including anthracyclines and specific targeted kinase inhibitors, can affect heart rhythm or cause QT-interval prolongation, which raises the risk of dangerous arrhythmias. A baseline ECG provides a benchmark of your heart's normal function before therapy begins. Regular monitoring allows doctors to detect subtle electrical disturbances early, giving them the opportunity to adjust drug doses, introduce protective cardiac medications, or pause treatment temporarily to safeguard your long-term wellbeing.

The ECG itself is the diagnostic test, requiring no blood draws or invasive instruments. However, it is frequently combined with blood biomarker assays to provide a complete picture of cardiac health. Clinicians often measure serum troponin levels and brain natriuretic peptide (BNP or NT-proBNP) alongside an ECG to assess myocardial injury or heart failure. An echocardiogram or cardiac MRI may also be requested if the ECG reveals abnormal conduction patterns or if more detailed imaging of the heart chambers is required.

An ECG is not specific to diagnosing any single cancer type; rather, it is used widely across oncology whenever treatment regimens carry potential cardiotoxic risks. It is frequently ordered for patients receiving therapy for breast cancer, leukaemia, lymphoma, colorectal cancer, and lung cancer. It is also an essential component of preoperative workups for individuals undergoing major surgical resections for abdominal, pelvic, thoracic, or head and neck tumours to ensure they can safely tolerate general anaesthesia.

If an ECG shows significant abnormalities, such as severe QT prolongation or arrhythmias, oncologists may modify the cancer treatment plan. This can involve dose reductions, switching to an alternative therapy with lower cardiac risk, or correcting underlying electrolyte imbalances such as hypokalaemia or hypomagnesaemia. Drugs known to affect cardiac rhythm—including certain tyrosine kinase inhibitors, immunotherapies, or anti-nausea medications—may be temporarily held until the electrical reading returns to a safe range under the guidance of a cardio-oncologist.