QT Prolongation Risk Calculator
Estimated Risk Assessment
When you’re prescribed an antipsychotic, the focus is usually on calming hallucinations, reducing paranoia, or stabilizing mood. But there’s another silent risk hiding in plain sight: your heart. Combining certain antipsychotics with other common medications can stretch out the electrical cycle of your heartbeat - a dangerous condition called QT prolongation - and trigger a life-threatening rhythm called torsades de pointes. This isn’t theoretical. Between 2010 and 2022, the FDA documented 128 cases of this deadly arrhythmia linked to these drug combinations. And it’s happening more than you think.
What QT Prolongation Actually Means
Your heart doesn’t just beat - it electrically resets after each beat. The QT interval on an ECG measures how long it takes your heart’s lower chambers to recharge. If that time gets too long, your heart can misfire. Normal QTc (corrected for heart rate) is under 440 ms for men and under 460 ms for women. Once it crosses 500 ms, your risk of sudden cardiac arrest jumps more than fivefold. That’s why doctors monitor it closely when you’re on certain meds.Which Antipsychotics Are Riskiest?
Not all antipsychotics are created equal when it comes to heart risk. Some block the hERG potassium channel - the same channel that keeps your heart rhythm steady - much more strongly than others. Thioridazine, for example, is one of the worst offenders, with an IC50 of just 0.04 μM. It was pulled from the U.S. market in 2005 because of cardiac deaths, but it’s still used elsewhere. Ziprasidone and haloperidol also rank high on the danger list. On the other end, drugs like aripiprazole, brexpiprazole, and lurasidone have weak hERG effects. Their IC50 values are over 10 μM, meaning they barely touch the channel. That’s why they’re now considered low-risk options. But here’s the problem: the most commonly prescribed antipsychotics aren’t the safest ones. Quetiapine and risperidone - used in over 40 million prescriptions a year - fall into the moderate-risk category. They’re effective, affordable, and widely available. But they’re also frequently paired with other drugs that make the danger worse.The Real Danger: Drug Combinations
The biggest threat isn’t one drug alone - it’s stacking them. About 45% of people on antipsychotics are also taking at least one other medication that prolongs QT. Common culprits include antibiotics like moxifloxacin, anti-nausea drugs like ondansetron, and even some antidepressants. When you combine them, the effect isn’t just added - it’s multiplied. A 2021 study showed that patients on both an antipsychotic and another QT-prolonging drug had QTc prolongation 2.3 to 4.7 times greater than those on just one. One case from Cleveland Clinic involved a 68-year-old woman on quetiapine and ciprofloxacin. Her QTc jumped from 448 ms to 582 ms in just three days. She nearly died. That’s not rare. The 2018 JAMA Internal Medicine study found that pairing antipsychotics with antidepressants increased torsades risk by 4.3 times. Ondansetron plus an antipsychotic? QTc went up by nearly 40 milliseconds more than the antipsychotic alone.
Who’s Most at Risk?
It’s not just about the drugs. Your body matters too. Women naturally have longer QT intervals - adding 12.8 ms on average. People over 65 add another 15.3 ms. Low potassium (below 3.5 mmol/L) adds 22.7 ms. Slow heart rate (under 50 bpm) adds 18.4 ms. If you’re a 70-year-old woman on risperidone, taking ondansetron for nausea, and you’ve had diarrhea lately? You’re sitting on a ticking time bomb. Even your genes play a role. About 7-10% of Caucasians are poor metabolizers of CYP2D6, a liver enzyme that breaks down many antipsychotics. These patients end up with much higher drug levels in their blood - up to 2.4 times higher - increasing their risk even if they’re on a “low-risk” drug.What Doctors Should Be Doing
The American Heart Association says you need a baseline ECG within a week of starting a moderate- or high-risk antipsychotic. If you’re on a combo, you need weekly ECGs for the first month, then monthly. That’s the guideline. But in real life? Only about 35% of community clinics follow it. Why? Insurance denies the tests. Rural clinics don’t have ECG machines. Doctors are overwhelmed. One clinician on a psychiatry forum said she spends nearly 10 minutes a day just dealing with false alerts from her EHR system. But there’s a better way. The University of Toronto’s 2022 study showed that when electronic alerts were added to prescribing systems, dangerous combinations dropped by 53%. That’s huge. And it’s not just about ECGs. Monitoring potassium and magnesium levels prevents 82% of torsades cases, according to a 2023 JAMA Cardiology study. Simple blood tests. Low cost. High impact.
What You Can Do
If you’re on an antipsychotic, ask these questions:- Is this drug known to affect my heart rhythm?
- Am I taking any other meds that might add to that risk - even over-the-counter ones?
- Have I had an ECG since I started this medication?
- What are my potassium and magnesium levels?
- Is there a safer alternative available?
The Changing Landscape
The tide is turning. Low-risk antipsychotics like aripiprazole are growing at 8.4% per year. By 2027, they’re expected to make up over half of new prescriptions. Why? Because CMS - the agency that runs Medicare - is starting to tie reimbursement to proper QT monitoring. Starting in 2025, 2.3% of Medicare Part D payments will depend on whether doctors follow cardiac safety guidelines. New tech is helping too. The FDA approved the Zio XT patch in 2024 - a wearable ECG monitor designed specifically for psychiatric patients. It can catch dangerous QT spikes in real time, without requiring a clinic visit. And by 2026, a genetic test will identify poor metabolizers before they even start a drug.The Bottom Line
Antipsychotics save lives. But they can also end them - especially when mixed with other drugs. The risk isn’t high for every patient. But for some, it’s deadly. The solution isn’t to avoid treatment. It’s to use smarter, safer tools: better drug choices, routine ECGs, electrolyte checks, and patient education. If you’re on one of these medications, don’t wait for a crisis. Ask your doctor: What’s my QTc? And make sure you know the answer.Can antipsychotics cause sudden cardiac death?
Yes, but it’s rare when monitored properly. The absolute risk of sudden cardiac death from QT prolongation in psychiatric patients is about 0.7% per year. However, when combined with other QT-prolonging drugs, or in high-risk patients (elderly, female, low potassium), the risk increases significantly. Most deaths occur within 72 hours of starting a new combination, which is why early monitoring is critical.
Are all antipsychotics equally dangerous for the heart?
No. High-risk antipsychotics like thioridazine, ziprasidone, and haloperidol strongly block the hERG channel and carry the highest risk. Moderate-risk drugs include quetiapine and risperidone. Low-risk options like aripiprazole, brexpiprazole, and lurasidone have minimal hERG effects and are safer choices, especially when other heart-affecting drugs are needed.
What other medications can worsen QT prolongation?
Common ones include antibiotics like moxifloxacin and ciprofloxacin, anti-nausea drugs like ondansetron and promethazine, certain antidepressants (citalopram, escitalopram), and some antiarrhythmics like sotalol. Even some over-the-counter antihistamines and herbal supplements like licorice root can lower potassium and increase risk.
How often should I get an ECG if I’m on an antipsychotic?
Baseline ECG should be done within one week of starting a moderate- or high-risk antipsychotic. If you’re on a combination with another QT-prolonging drug, weekly ECGs for the first month, then monthly, are recommended. For single-agent therapy with moderate risk, ECGs at 1 week, 4 weeks, and then every 3 months are standard. Low-risk drugs typically don’t require routine monitoring unless other risk factors are present.
Can I avoid this risk by switching medications?
Yes, in many cases. Switching from a high- or moderate-risk antipsychotic to a low-risk option like aripiprazole or lurasidone can dramatically reduce cardiac risk - especially if you’re already on other QT-prolonging drugs. Many patients stabilize just as well on these alternatives. Talk to your doctor about whether a switch is appropriate for your situation.
Is it safe to take antipsychotics if I have a history of heart problems?
It’s possible, but requires extra caution. If you have a history of arrhythmias, heart failure, or long QT syndrome, your doctor should avoid high-risk antipsychotics entirely. Low-risk options are preferred, and ECG monitoring must be more frequent. You may also need a cardiologist involved in your care. Never stop your medication without medical guidance - but do insist on a full cardiac risk assessment before starting or changing treatment.
