{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"qtc-interval"},"result":{"entity_type":"calculator","id":"qtc-interval","calculator_id":"qtc-interval","canonical_url":"https://tttkmbb.com/medical/qtc-interval","name":"QTc Calculator","title":"Corrected QT Interval (QTc) Calculator – Bazett, Fridericia, Framingham and Hodges","category":"medical","category_name":"Medical & Clinical","tool_name":"calculate_qtc_interval","featured_mcp_tool":false,"description":"Corrects a measured QT interval for heart rate with the Bazett, Fridericia, Framingham and Hodges formulas and flags prolongation against the sex-specific thresholds (450 ms men, 460 ms women).","use_when":"You have a QT interval in ms and a heart rate (or RR interval) from an ECG and need the rate-corrected QTc or a prolongation check.","do_not_use_when":"The rhythm is irregular (atrial fibrillation) or QRS is wide (bundle branch block, paced rhythm), where standard QTc formulas are unreliable.","inputs":[{"name":"qt_ms","label":"QT interval","type":"number","unit":"ms","required":true,"min":150,"max":800,"description":"Measured QT interval in milliseconds.","example":400},{"name":"heart_rate_bpm","label":"Heart rate","type":"number","unit":"bpm","required":false,"min":20,"max":300,"description":"Heart rate in beats per minute (RR = 60000 / HR). Give this or rr_interval_ms.","example":75},{"name":"rr_interval_ms","label":"RR interval","type":"number","unit":"ms","required":false,"min":200,"max":3000,"description":"Optional RR interval in ms, used instead of heart rate when given.","example":800},{"name":"sex","label":"Sex","type":"enum","required":true,"values":[{"value":"male","label":"Male","aliases":["m","man"]},{"value":"female","label":"Female","aliases":["f","woman"]}],"description":"Sex used to select the formula coefficients or thresholds.","example":"male"}],"outputs":[{"name":"rr_interval_ms","label":"RR interval","type":"number","unit":"ms","decimals":0,"description":"RR interval used for the corrections."},{"name":"qtc_bazett_ms","label":"QTc (Bazett)","type":"number","unit":"ms","decimals":0,"description":"QT / √RR (RR in s)."},{"name":"qtc_fridericia_ms","label":"QTc (Fridericia)","type":"number","unit":"ms","decimals":0,"description":"QT / RR^(1/3)."},{"name":"qtc_framingham_ms","label":"QTc (Framingham)","type":"number","unit":"ms","decimals":0,"description":"QT + 154 × (1 − RR)."},{"name":"qtc_hodges_ms","label":"QTc (Hodges)","type":"number","unit":"ms","decimals":0,"description":"QT + 1.75 × (HR − 60)."},{"name":"threshold_ms","label":"Prolongation threshold","type":"number","unit":"ms","decimals":0,"description":"450 ms for men, 460 ms for women (AHA/ACCF/HRS 2009)."},{"name":"interpretation","label":"Interpretation","type":"string","decimals":4,"description":"Normal, prolonged or markedly prolonged (>500 ms), judged on Bazett at 60–100 bpm and Fridericia outside that range."}],"input_schema":{"type":"object","properties":{"qt_ms":{"description":"Measured QT interval in milliseconds. Unit: ms.","type":"number","minimum":150,"maximum":800,"examples":[400],"x-unit":"ms"},"heart_rate_bpm":{"description":"Heart rate in beats per minute (RR = 60000 / HR). Give this or rr_interval_ms. Unit: bpm.","type":"number","minimum":20,"maximum":300,"examples":[75],"x-unit":"bpm"},"rr_interval_ms":{"description":"Optional RR interval in ms, used instead of heart rate when given. Unit: ms.","type":"number","minimum":200,"maximum":3000,"examples":[800],"x-unit":"ms"},"sex":{"description":"Sex used to select the formula coefficients or thresholds.","type":"string","enum":["male","female"],"examples":["male"]}},"additionalProperties":false,"required":["qt_ms","sex"]},"output_schema":{"type":"object","properties":{"rr_interval_ms":{"description":"RR interval used for the corrections. Unit: ms.","type":"number","x-unit":"ms"},"qtc_bazett_ms":{"description":"QT / √RR (RR in s). Unit: ms.","type":"number","x-unit":"ms"},"qtc_fridericia_ms":{"description":"QT / RR^(1/3). Unit: ms.","type":"number","x-unit":"ms"},"qtc_framingham_ms":{"description":"QT + 154 × (1 − RR). Unit: ms.","type":"number","x-unit":"ms"},"qtc_hodges_ms":{"description":"QT + 1.75 × (HR − 60). Unit: ms.","type":"number","x-unit":"ms"},"threshold_ms":{"description":"450 ms for men, 460 ms for women (AHA/ACCF/HRS 2009). Unit: ms.","type":"number","x-unit":"ms"},"interpretation":{"description":"Normal, prolonged or markedly prolonged (>500 ms), judged on Bazett at 60–100 bpm and Fridericia outside that range.","type":"string"}}},"formula":"RR (s) = 60 / heart_rate_bpm (or rr_interval_ms / 1000). Bazett: QTc = QT / √RR. Fridericia: QTc = QT / RR^(1/3). Framingham: QTc = QT + 154 × (1 − RR). Hodges: QTc = QT + 1.75 × (heart_rate − 60).","method":"Bazett over-corrects at fast rates and under-corrects at slow rates, so Fridericia is used for the interpretation when heart rate is outside 60–100 bpm; QTc above 500 ms is associated with a higher risk of torsades de pointes. Results are informational only and not a substitute for clinical judgement or medical advice.","sources":[{"name":"Rautaharju PM et al. (2009) AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram, part IV: the ST segment, T and U waves, and the QT interval, Circulation 119:e241-e250","url":"https://pubmed.ncbi.nlm.nih.gov/19228821/","type":"standard","retrieved_at":"2026-09-24"},{"name":"Fridericia LS (1920, reprinted 2003) The duration of systole in an electrocardiogram in normal humans and in patients with heart disease, Ann Noninvasive Electrocardiol 8:343-351","url":"https://pubmed.ncbi.nlm.nih.gov/14516292/","type":"peer_reviewed","retrieved_at":"2026-09-24"},{"name":"Wikipedia – QT interval (Bazett 1920 and other correction formulas)","url":"https://en.wikipedia.org/wiki/QT_interval","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"QT 400 ms, 75 bpm, male","inputs":{"qt_ms":400,"heart_rate_bpm":75,"sex":"male"},"expected":{"rr_interval_ms":800,"qtc_bazett_ms":447,"qtc_fridericia_ms":431,"qtc_framingham_ms":431,"qtc_hodges_ms":426,"threshold_ms":450,"interpretation":"Normal (Bazett QTc 447 ms ≤ 450 ms for men)"},"url":"https://tttkmbb.com/api/v1/calculate/qtc-interval?qt_ms=400&heart_rate_bpm=75&sex=male"},{"name":"QT 440 ms, 100 bpm, female","inputs":{"qt_ms":440,"heart_rate_bpm":100,"sex":"female"},"expected":{"qtc_bazett_ms":568,"qtc_fridericia_ms":522,"qtc_framingham_ms":502,"qtc_hodges_ms":510,"interpretation":"Markedly prolonged (Bazett QTc 568 ms > 500 ms)"},"url":"https://tttkmbb.com/api/v1/calculate/qtc-interval?qt_ms=440&heart_rate_bpm=100&sex=female"}],"faq":[{"q":"Which formula is best?","a":"Bazett is the most widely used and the basis of most reference thresholds, but Fridericia and Framingham track risk better at heart rates outside 60–100 bpm; drug-safety studies usually report Fridericia."},{"q":"How should QT be measured?","a":"From the start of the QRS to the end of the T wave in lead II or V5, averaged over several beats; automated ECG readings can mis-measure the T-wave end."}],"tags":["qtc","qt interval","bazett","fridericia","long qt","ecg"],"related":[{"calculator_id":"heart-rate-zones","reason":"Heart-rate context for exercise ECGs."}],"links":{"html":"https://tttkmbb.com/medical/qtc-interval","markdown":"https://tttkmbb.com/medical/qtc-interval.md","json":"https://tttkmbb.com/medical/qtc-interval.json","api":"https://tttkmbb.com/api/v1/calculate/qtc-interval","schema":"https://tttkmbb.com/api/v1/calculators/qtc-interval","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T01:48:12Z","next_actions":[{"tool":"run_calculator","calculator_id":"qtc-interval","reason":"Run QTc Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/medical/qtc-interval.md"}}