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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Cardiology

Understanding Your ECG and Genetic Test Reports

At a Glance

Congenital long QT syndrome (LQTS) is diagnosed using both ECG readings, like the QTc measurement, and genetic testing. Finding a pathogenic genetic mutation allows for cascade screening to protect family members, even if their ECGs appear completely normal.

Understanding your medical reports is a powerful way to take control of your care. When you look at an ECG or a genetic test result, you are looking at two different “languages” that doctors use to build a complete picture of your heart’s health.

The ECG Report: Measuring the “Recharge”

The most important number on your ECG report is the QTc.

  • QT Interval: This is the actual time (in milliseconds) it takes for your heart to electrically reset [1].
  • QTc (Corrected QT): Because your heart naturally resets faster when it beats quickly (like during exercise), doctors must “correct” the measurement for your heart rate to see if the timing is truly abnormal [2].
  • The Formula: Most reports use Bazett’s Formula (QTc=QTRRQTc = \frac{QT}{\sqrt{RR}}). While standard, this formula can sometimes overestimate the risk at high heart rates, so your doctor may also look at other calculations like Fridericia’s to get a more accurate view [2][3].

The Schwartz Score: A Diagnostic Checklist

Doctors don’t just look at one number; they use a point-based system called the Schwartz Score to determine the probability of LQTS [4]. Points are awarded for:

  • ECG Findings: Longer QTc measurements and specific “notched” T-wave shapes [4].
  • Clinical History: Fainting spells (especially those triggered by stress or exercise) or unexplained deafness [4].
  • Family History: Close relatives with known LQTS or sudden, unexplained deaths at a young age [4].
    A score of 3.5 or higher suggests a high probability of LQTS [5].

Reading the Genetic Report

Genetic testing looks for “typos” in your DNA. The results are usually classified into three main categories [6]:

  1. Pathogenic or Likely Pathogenic: This is a “positive” result. It means a mutation was found that is known to cause LQTS [6][7].
  2. Variant of Uncertain Significance (VUS): This is a “gray area” result. A change was found in the DNA, but scientists don’t yet have enough data to know if it causes disease or is just a normal, harmless variation [6][8]. A VUS should generally not be used to make major medical decisions for other family members [6].
  3. Benign: No disease-causing mutations were found.

Genotype-Positive vs. Phenotype-Negative

You may hear these terms if your genetic test is positive but your ECG looks normal.

  • Genotype-Positive: You carry the genetic mutation for LQTS [9].
  • Phenotype-Negative: Your heart’s physical “expression” (the ECG) appears normal [9].
    This is often called concealed LQTS [10]. While these individuals have a lower risk of sudden events than those with long QTc intervals, they must still be cautious with certain medications and triggers [11][10][9].

Cascade Screening: Protecting the Family

If a pathogenic mutation is found, your medical team will recommend cascade screening [12]. This is the systematic process of testing your parents, siblings, and children for that same specific mutation [12][13].

  • Why it matters: Because of “concealed” LQTS, a relative might have a normal ECG but still carry the gene [14][15]. Finding the gene through cascade screening allows them to take simple, life-saving precautions [12][16].
  • Efficiency: Instead of testing every heart gene, doctors can look specifically for the “typo” already identified in your family, making the process faster and more accurate [17].

Common questions in this guide

What does the QTc number on my ECG report mean?
The QTc is your heart's electrical reset time corrected for your heart rate. It is the most important number on your ECG report for evaluating long QT syndrome risk, as your heart naturally resets faster when it beats quickly.
What is a Schwartz score?
The Schwartz score is a diagnostic checklist that helps doctors determine the probability of long QT syndrome. It assigns points based on your ECG findings, clinical history like fainting, and family history. A score of 3.5 or higher suggests a high probability of the condition.
What does a Variant of Uncertain Significance (VUS) mean on my genetic report?
A VUS means a change was found in your DNA, but scientists do not yet have enough data to know if it causes disease or is just a normal, harmless variation. This result should generally not be used to make major medical decisions for other family members.
What is concealed LQTS (genotype-positive, phenotype-negative)?
Concealed LQTS occurs when a person carries the genetic mutation for the condition, but their physical ECG results appear completely normal. Even though their risk of sudden events is lower, people with concealed LQTS still need to be cautious with certain medications and triggers.
Why is cascade screening recommended for my family members?
Cascade screening is the systematic process of testing your parents, siblings, and children for the specific genetic mutation found in your family. It is crucial because a relative might have a normal ECG but still carry the gene and require simple, life-saving precautions.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What was the specific QTc measurement, and which correction formula (like Bazett or Fridericia) was used to calculate it?
  2. 2.Based on our history and ECG, what is our Schwartz score, and what does that tell us about the certainty of the diagnosis?
  3. 3.The genetic report mentions a 'VUS'—is there a plan to re-evaluate this variant as more data becomes available in the future?
  4. 4.Since we found a pathogenic mutation, can you provide a letter or information to help us begin cascade screening for other family members?
  5. 5.For family members with 'concealed' LQTS, what specific safety protocols must they follow even if their ECG is normal?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
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    CONGENITAL LONG QT SYNDROME: A SYSTEMATIC REVIEW.

    Galić E, Bešlić P, Kilić P, et al.

    Acta clinica Croatica 2021; (60(4)):739-748 doi:10.20471/acc.2021.60.04.22.

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    Problems with Bazett QTc correction in paediatric screening of prolonged QTc interval.

    Andršová I, Hnatkova K, Helánová K, et al.

    BMC pediatrics 2020; (20(1)):558 doi:10.1186/s12887-020-02460-8.

    PMID: 33317470
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    Reproducibility of corrected QT interval in pediatric genotyped long QT syndrome.

    Ogawa Y, Tanaka T, Kido S

    Pediatrics international : official journal of the Japan Pediatric Society 2016; (58(11)):1246-1248 doi:10.1111/ped.13120.

    PMID: 27882731
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    All the things that we should think about if we want to diagnose the long QT accurately.

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    Pacing and clinical electrophysiology : PACE 2019; (42(2)):293 doi:10.1111/pace.13575.

    PMID: 30548640
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    The Yield of Genetic Testing and Putative Genetic Factors of Disease Heterogeneity in Long QT Syndrome Patients.

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    International journal of molecular sciences 2024; (25(22)) doi:10.3390/ijms252211976.

    PMID: 39596046
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    Pre-Test Probability and Genes and Variants of Uncertain Significance in Familial Long QT Syndrome.

    Waddell-Smith KE, Skinner JR, Bos JM

    Heart, lung & circulation 2020; (29(4)):512-519 doi:10.1016/j.hlc.2019.12.011.

    PMID: 32044265
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    Case Report Series: Genetic and clinical characterization of long QT syndrome in admixed Ecuadorian patients and its implications for sudden cardiac death risk.

    Paz-Cruz E, Ruiz-Pozo VA, Cadena-Ullauri S, et al.

    Frontiers in cardiovascular medicine 2026; (13()):1680300 doi:10.3389/fcvm.2026.1680300.

    PMID: 41768584
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    GENESIS: Gene-Specific Machine Learning Models for Variants of Uncertain Significance Found in Catecholaminergic Polymorphic Ventricular Tachycardia and Long QT Syndrome-Associated Genes.

    Draelos RL, Ezekian JE, Zhuang F, et al.

    Circulation. Arrhythmia and electrophysiology 2022; (15(4)):e010326 doi:10.1161/CIRCEP.121.010326.

    PMID: 35357185
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    Diagnosis, management and therapeutic strategies for congenital long QT syndrome.

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    PMID: 34039680
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    A case of congenital long QT syndrome, type 8, undergoing laparoscopic hysterectomy with general anesthesia.

    Chang SL, Chang CT, Hung WT, Chen LK

    Taiwanese journal of obstetrics & gynecology 2019; (58(4)):552-556 doi:10.1016/j.tjog.2019.05.031.

    PMID: 31307750
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    The Long QT Syndrome: A Review and Mortality Analysis.

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    Journal of insurance medicine (New York, N.Y.) 2015; (45(2)):81-7 doi:10.17849/insm-45-02-081-087.1.

    PMID: 27584843
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    Results of comprehensive genetic testing in patients presenting to a multidisciplinary inherited heart disease clinic in India.

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    Molecular genetics in 1991 arrhythmia probands and 2782 relatives in Norway: Results from 17 years of genetic testing in a national laboratory.

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    Late-onset severe long QT syndrome.

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    Exploring the impact of a KCNH2 missense variant on Long QT syndrome: insights into a novel gender-selective, incomplete penetrance inheritance mode.

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    Identification and characterization of a novel recessive KCNQ1 mutation associated with Romano-Ward Long-QT syndrome in two Iranian families.

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    Use of a chatbot to increase uptake of cascade genetic testing.

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This page explains long QT syndrome ECG and genetic test terminology for educational purposes. Your cardiologist and genetic counselor are the best sources for interpreting your specific medical reports.

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