Abnormal ECG in Multiple Myeloma: What It Means and When to Be Concerned

An abnormal ECG (electrocardiogram) in someone with multiple myeloma can have several explanations, and not all are dangerous; however, it’s wise to pay attention because heart rhythm and electrical changes can reflect disease effects, treatment side effects, or unrelated heart issues. In many cases, ECG changes are due to treatable factors like electrolyte imbalances or medication effects, but they can also signal heart involvement that needs timely evaluation.

How Multiple Myeloma Can Affect the Heart

• Anemia and thickened blood (hyperviscosity) can strain the heart and contribute to symptoms like fatigue, shortness of breath, or palpitations, which sometimes accompany ECG changes. Myeloma often causes anemia and elevated blood proteins that thicken the blood. ^{[1] [2]}
• High calcium (hypercalcemia) from bone involvement can disturb heart electrical signaling and provoke arrhythmias or ECG abnormalities. Elevated blood calcium is a known feature of myeloma due to bone breakdown. ^{[1] [3]}
• Kidney problems caused by myeloma proteins can alter electrolytes (potassium, magnesium, calcium), which are essential for normal heart rhythms; disturbances often show up as ECG changes. Myeloma often affects the kidneys, which in turn can influence electrolyte balance. ^[3]

Key idea: Systemic effects of myeloma anemia, high calcium, and kidney-related electrolyte changes can each lead to abnormal ECG readings. ^{[1] [3]}

Cardiac Amyloidosis: A Specific Concern

Some people with myeloma develop light‑chain (AL) amyloidosis, where abnormal light chains deposit in the heart muscle. This can cause thickened heart walls with “low‑voltage” signals on ECG, arrhythmias, and heart failure symptoms (shortness of breath, swelling, fainting). Low‑voltage ECGs and rhythm issues are commonly described in cardiac amyloidosis. ^{[4] [5]}
AL amyloidosis is a myeloma‑related condition in which light chains misfold and deposit in organs, including the heart. ^{[6] [7]}

Practical takeaway: If your ECG shows low voltage or conduction abnormalities and you have signs like leg swelling, breathlessness, or fainting, clinicians often consider screening for cardiac amyloidosis. ^{[4] [5]}

Treatment Effects That Can Alter the ECG

• Chemotherapy and cancer therapies can sometimes affect heart rhythm and conduction, causing arrhythmias or QT interval changes on ECG. Such effects are recognized across multiple cancer treatments and may require monitoring. ^{[8] [9]}
• Certain regimens used in AL amyloidosis (for example, combinations including daratumumab) are given to many patients who already have cardiac involvement, and serious cardiac events can occur, especially in advanced cardiac stages; close monitoring is recommended. ^{[10] [11]}
• Not all agents prolong QT; for example, siltuximab did not show large average QT changes in a study of gammopathy/myeloma spectrum patients, illustrating that effects vary by drug. ^{[12] [13] [14]}

Bottom line: Some myeloma therapies can influence ECG findings, particularly QT interval and arrhythmias, so clinicians often check ECGs and electrolytes before and during treatment. ^{[9] [15]}

What Specific ECG Abnormalities Might Mean

• Low voltage: Often associated with cardiac amyloidosis and thickened heart walls but weak electrical signals. ^{[4] [5]}
• Prolonged QTc: Increases risk of dangerous arrhythmias; cancer therapies, electrolyte problems, and other medications can contribute. Monitoring and dose adjustments are typically guided by thresholds (for example, holding treatment if QTc is above certain cutoffs and correcting electrolytes). ^{[16] [17]}
• Arrhythmias (irregular rhythms): Can be due to amyloidosis, anemia, electrolyte issues, or treatment effects; may need antiarrhythmic therapy and close observation in high‑risk settings. In AL amyloidosis, there’s a recognized risk of life‑threatening arrhythmias, prompting cardiac monitoring around intensive treatments. ^{[18] [19]}

When to Be Concerned

You should be more alert and seek prompt medical review if you notice any of the following alongside an abnormal ECG:

• Symptoms: chest pain, fainting, severe shortness of breath, new leg swelling, or rapid/fluctuating heartbeats. AL amyloidosis can present with rapidly progressive heart failure and arrhythmias. ^[5]
• Marked QTc prolongation: Many oncology protocols advise interrupting or adjusting therapy if QTc crosses certain thresholds (e.g., >480–500 ms), and to correct potassium, magnesium, and calcium. ^{[16] [17]}
• New kidney or calcium abnormalities: Because they can trigger rhythm changes and ECG abnormalities. Myeloma commonly causes hypercalcemia and kidney involvement, making electrolyte monitoring important. ^{[3] [1]}

Practical Steps You Can Take

• Ask your team what specific ECG change was found (e.g., low voltage, prolonged QT, arrhythmia) and how it was measured. This directs next steps.
• Check and correct electrolytes (potassium, magnesium, calcium), especially during treatment cycles; this is standard practice in oncology to reduce arrhythmia risk. ^{[16] [17]}
• Review medications for QT‑prolonging or arrhythmia‑inducing effects; your clinicians may adjust doses or switch agents as per established thresholds and monitoring schedules. ^{[15] [16]}
• Consider cardiac evaluation (echocardiogram, biomarkers, cardiac MRI) if there’s suspicion for amyloidosis or if symptoms are present; low‑voltage ECG with thickened heart walls often prompts such work‑ups. ^{[4] [5]}
• Ongoing monitoring: Baseline and interval ECGs and blood tests are commonly used during cancer treatment, especially if heart‑affecting therapies are planned or if you have preexisting heart risk. ^{[9] [19]}

The Big Picture

• Abnormal ECGs in multiple myeloma are not uncommon and can stem from the disease itself, related conditions like AL amyloidosis, treatment side effects, or general electrolyte/medical issues. Paying attention is appropriate, but many causes are manageable with timely evaluation and correction. ^{[1] [5]}
• Your care team typically follows clear safety thresholds for QTc and arrhythmias, monitors electrolytes, and adapts therapies to reduce risk. This proactive approach helps keep treatment on track while protecting the heart. ^{[15] [16]}

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