Why Some Cancer Treatments Require Cardiac Monitoring

This page is for people on cancer treatments that can affect the heart, such as anthracyclines or trastuzumab. It explains why heart scans are scheduled, what they measure, and which symptoms need a call.

• Call 911 or go to an emergency department if chest discomfort does not pass within a few minutes, if you cannot catch your breath at rest or wake up gasping, or if you faint or nearly faint. Do not wait to see whether it settles. Do not drive yourself.
• Call your care team the same day if your heart is racing or beating irregularly, if breathlessness has appeared with mild activity or when lying flat, or if the scale has jumped over just a few days.
• Call your care team within a day or two if your ankles, legs, or abdomen have begun to swell, or if unusual fatigue and dizziness have crept in.

These symptoms have many harmless causes during cancer treatment. But they are worth checking, rather than waiting until your next scheduled echocardiogram (heart ultrasound).

A few cancer treatments that work well can also weaken the heart's pumping. Monitoring exists because that weakening:

• Can develop during treatment or up to several years after it ends.
• Can show up on a scan as a drop in ejection fraction.
• Can be present before heart failure symptoms appear.
• Gives your team more options when it is caught early.

Having echocardiograms scheduled does not mean your heart is failing. The scans are how teams keep that from happening.

Left ventricular ejection fraction, or LVEF, is the share of blood the heart's main pumping chamber pushes out with each beat. A normal heart does not empty completely. FDA labels for these drugs treat 50% or higher as normal.

The number comes from one of a few tests. An echocardiogram uses an ultrasound of the heart, involving gel and a probe. A MUGA scan is a nuclear medicine test that can measure the same thing. The FDA labels name either test for checking heart function.

Your team watches the trend more than any single value. A drop from your own starting number matters more than where you fall in the normal range.

Doxorubicin carries a boxed warning (the FDA's strongest label warning) for heart muscle damage. The risk grows with the total dose received over a lifetime.

The doxorubicin label says the chance of heart muscle damage rises as the total dose adds up. It can appear during treatment or up to several years after. What matters on your side is that your team is keeping track of your total.

This is why oncologists track lifetime dose carefully. It is also why the label advises checking heart function before treatment, during it, and afterward, with closer checks as the total grows. Radiation to the chest area and other heart-affecting drugs given alongside, such as cyclophosphamide and trastuzumab, add to the risk.

Trastuzumab can cause a decline in ejection fraction, with the greatest risk when it is given together with anthracyclines. The Herceptin label we checked recommends this schedule: a measurement just before starting, every 3 months during treatment and at completion, then every 6 months for at least two years after adjuvant therapy finishes. (Adjuvant therapy is treatment given after surgery to lower the chance of the cancer coming back.) Your team calendars those scans; keeping them is your half of the arrangement.

The label defines exactly how large a fall from your own baseline forces a hold, and how often to remeasure while holding — numeric rules your oncologist and cardiologist apply to your scans, not ones to apply yourself. Treatment often restarts once the number recovers.

The FDA labels point to a few situations that raise the risk:

• Higher total (cumulative) anthracycline dose.
• Radiation to the chest area.
• Trastuzumab given together with, or soon after, an anthracycline.

Other factors, such as age and existing heart disease, also matter to your team. Ask which ones apply to you.

A fall in LVEF typically leads to a few things:

• Doctors hold the drug rather than abandoning treatment.
• They refer you to cardiology or a cardio-oncology (heart care for people with cancer) clinic.
• They may start heart medicines. Ask which ones and why.

Decisions about going on with cancer treatment are made together. Your team weighs your cancer risk against your heart risk. These decisions are individual, not automatic.

• FDA - Doxorubicin Hydrochloride Injection prescribing information.
• FDA - Herceptin (trastuzumab) prescribing information. This is an older label version, so ask your team about current monitoring.
• MedlinePlus - Heart failure.