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CredibleMeds (crediblemeds.org) maintains a regularly updated database of QT-prolonging drugs categorized by risk level — worth bookmarking for clinical reference.","type":"text","version":1}],"direction":"ltr","format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""},{"type":"horizontalrule","version":1},{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Limitations and Accuracy Considerations","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"heading","version":1,"tag":"h2"},{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"When Formulas Disagree","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"heading","version":1,"tag":"h3"},{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"If Bazett and Fridericia give QTc values more than 20-30 ms apart, trust Fridericia for heart rates below 60 or above 100 bpm. 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36:["$","div",null,{"className":"bg-white rounded-lg shadow-sm p-8","children":[["$","h2",null,{"className":"typo-large mb-6 text-mist-950","children":"Frequently Asked Questions"}],["$","div",null,{"className":"space-y-6","children":[["$","div","0",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"What is a normal QTc value?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"For men, normal QTc is generally below 430 ms, with 430-450 ms considered borderline. For women, normal extends to 450 ms, with 450-470 ms borderline. These thresholds reflect natural sex-based differences in cardiac repolarization.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}],["$","div","1",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"When is QTc considered dangerously prolonged?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Most clinicians consider QTc above 500 ms a serious concern — the risk of Torsades de Pointes arrhythmia increases substantially beyond this point. Values between 470-500 ms warrant close monitoring, medication review, and electrolyte optimization.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}],["$","div","2",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"Which QTc formula should I use — Bazett or Fridericia?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"For heart rates between 60-100 bpm, Bazett works fine and matches most reference standards. Outside this range, Fridericia gives more accurate results. When in doubt, look at both — if they're similar, either is reliable. If they diverge significantly, lean toward Fridericia.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}],["$","div","3",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"Why does my QTc look different on different monitors?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Automated ECG algorithms vary in how they detect the end of the T wave, especially when the T wave is flat or merged with a U wave. Manual measurement using a consistent technique gives more reliable serial comparisons than automated readings from different machines.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}],["$","div","4",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"Does QTc differ between men and women?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Yes. Women have naturally longer QT intervals, which is why normal thresholds differ by sex. Women are also at higher risk of drug-induced QT prolongation and Torsades de Pointes — something to factor in when prescribing QT-prolonging medications.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}],"$L38","$L39","$L3a","$L3b","$L3c"]}]]}]
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38:["$","div","5",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"What medications can prolong my QT interval?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Common culprits include antiarrhythmics (sotalol, amiodarone), certain antibiotics (fluoroquinolones, azithromycin), antipsychotics (haloperidol, ziprasidone), and some antiemetics (ondansetron). Combinations are particularly dangerous — two drugs with modest QT effects can add up to a big problem.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}]
39:["$","div","6",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"Can anxiety or stress affect QT measurements?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Indirectly, yes. Stress and anxiety increase heart rate and catecholamine levels, which can affect the QT interval. For the most reliable baseline measurement, try to obtain the ECG when your patient is calm and resting.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}]
3a:["$","div","7",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"How do I measure QT interval on an ECG strip?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Measure from the very start of the QRS complex to where the T wave returns to baseline. Use a lead with a clear T wave ending — II or V5 usually work well. If the T wave end is ambiguous, draw a tangent line along its steepest downslope and mark where that line crosses the baseline.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}]
3b:["$","div","8",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"What is Torsades de Pointes and why does prolonged QTc matter?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Torsades de Pointes (\"twisting of the points\") is a polymorphic ventricular tachycardia that can degenerate into ventricular fibrillation and sudden death. Prolonged QTc creates the electrical substrate for this arrhythmia — the longer the QT, the higher the risk.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}]
3c:["$","div","9",{"className":"pb-6 last:pb-0","children":[["$","h3",null,{"className":"text-lg font-medium text-mist-950 mb-3","children":"Should I use the RR interval or heart rate for calculation?"}],["$","div",null,{"className":"prose max-w-none text-mist-600","children":["$","$L33",null,{"content":{"root":{"children":[{"children":[{"detail":0,"format":0,"mode":"normal","style":"","text":"Either works — they're mathematically convertible (RR in seconds = 60/HR). This calculator accepts heart rate and automatically derives the RR interval. If you have the RR interval directly from the ECG, you can convert it to heart rate first, or use the relationship: RR (ms) = 60,000 / HR.","type":"text","version":1}],"direction":null,"format":"","indent":0,"type":"paragraph","version":1,"textFormat":0,"textStyle":""}],"direction":null,"format":"","indent":0,"type":"root","version":1}}}]}]]}]
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