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  • Writer's pictureGraham Exelby

QT Prolongation

Normal QTc Values by Age and Gender (Bazzet formula)





The sympathetic nervous system is responsible for regulating heart rate, blood pressure, and cardiac contractility. Increased sympathetic tone, as seen in sympathetic overactivity, can lead to an increase in heart rate and contractility, which in turn can prolong the QT interval.





Source: https://commons.wikimedia.org/wiki/File:QT_interval.jpg#/media/File:QT_interval.jpg



The QT interval is a measurement on an electrocardiogram (ECG) that represents the duration of ventricular depolarization and repolarization. It is measured from the start of the QRS complex (which represents ventricular depolarization) to the end of the T wave (which represents ventricular repolarization).


It is generally accepted that QT prolongation past 500 ms carries an increased risk of torsades de pointes. The degree of QT prolongation is correlated to the level of risk, with severe prolongations being associated with much higher risk.


A normal QT interval varies depending on heart rate, age, and sex, but typically ranges between 0.36 and 0.44 seconds. Prolongation of the QT interval can be a sign of certain cardiac conditions, medications, or electrolyte imbalances, and can increase the risk of developing arrhythmias.


Sympathetic overactivity can contribute to prolongation of the QT interval on an electrocardiogram (ECG) by increasing the duration of ventricular repolarization. The QT interval represents the time between the start of ventricular depolarization and the end of ventricular repolarization.


Several studies have shown an association between sympathetic overactivity and QT prolongation in various clinical settings, such as in patients with hypertension, heart failure, and diabetes. This relationship has also been observed in healthy individuals during physical and emotional stress.


Understanding the relationship between sympathetic overactivity and QT prolongation is important for the management of patients with cardiovascular disease.


From the findings of a high incidence of QT prolongation in POTS, Long Covid and dysautonomia, David Haynes (Kiiko-Matsumoto) has been researching with the research group, and has found this style of acupuncture can normalize the QT interval.


This has many ramifications in POTS and Long Covid management, as QT prolongation is often aggravated by the medications in use to stabilize the inflammatory activity. It is often needed before any pharmacotherapy can commence.


The most commonly used QT correction formula is the Bazett's formula, named after physiologist Henry Cuthbert Bazett (1885–1950).


The most common aetiology is acquired prolongation due to medication use, followed by electrolyte abnormalities. Covid has a high incidence of auto-immune disease, most commonly Hashimotos, and there is a known association between the two.


Low magnesium, potassium and calcium are potential causes, and especially when blocking mast cells, needs to be carefully watched for.


QT-Prolonging Medications


  • Antipsychotics: Haloperidol, ziprasidone, quetiapine, thioridazine, olanzapine, risperidone, droperidol, Chlorpromazine, clozapine, galantamine, haloperidol, lithium, paliperidone, pimozide

  • Antiarrhythmics: Amiodarone, sotalol, procainamide, quinidine, flecainide

  • Antibiotics: Macrolides, fluoroquinolones, erythromycin

  • Antidepressants: Amitriptyline, imipramine, citalopram, doxepin, fluoxetine, nortriptyline, paroxetine, sertraline, venlafaxine

  • Antifungals: Fluconazole, itraconazole, ketoconazole, voriconazole

  • Antihypertensives: Nicardipine

  • Antineoplastics: Lapatinib, nilotinib, sunitinib, tamoxifen

  • Antimalarials: Chloroquin

  • Immune suppressants: Tacrolimus

  • Phosphodiesterase inhibitors: Sidenafil, Vardenafil

  • Others: Methadone, sumatriptan, ondansetron, indipamide, cocaine, grapefruit juice


References:


Luca Sala, Massimiliano Gnecchi, Peter J Schwartz. Arrhythmia & Electrophysiology Review 2019;8(2):105–10. DOI: https://doi.org/10.15420/aer.2019.1.1

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