What Is A Normal QTc Calculation On An ECG

QTc Formula:

\[ QTc = \frac{QT}{\sqrt{RR}} \]

Corrected QT Interval (QTc):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What Is A Normal QTc Calculation On An ECG?

The QTc (corrected QT interval) is a heart rate-adjusted measurement of the QT interval on an electrocardiogram (ECG). It represents the time from the start of the Q wave to the end of the T wave, corrected for heart rate. Normal values are <440 ms for men and <460 ms for women.

2. How Does The Calculator Work?

The calculator uses the Bazett formula:

\[ QTc = \frac{QT}{\sqrt{RR}} \]

Where:

\( QT \) — Measured QT interval from start of Q wave to end of T wave (ms)
\( RR \) — RR interval = 60 / HR (seconds)
\( HR \) — Heart rate (beats per minute)

Explanation: The formula corrects the QT interval for heart rate variations, allowing comparison across different heart rates.

3. Importance Of QTc Calculation

Details: QTc measurement is crucial for detecting prolonged QT intervals, which can indicate increased risk of life-threatening arrhythmias such as torsades de pointes. It's essential in cardiac risk assessment and medication safety monitoring.

4. Using The Calculator

Tips: Enter the measured QT interval in milliseconds, heart rate in beats per minute, and select gender. All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is QTc correction necessary?
A: The QT interval naturally varies with heart rate. Correction allows comparison of QT values across different heart rates and between individuals.

Q2: What are the clinical implications of prolonged QTc?
A: Prolonged QTc (>440 ms men, >460 ms women) increases risk of ventricular arrhythmias and sudden cardiac death, particularly with certain medications or congenital conditions.

Q3: How is the QT interval measured on ECG?
A: From the beginning of the QRS complex to the end of the T wave, typically in lead II or V5 where T waves are most clearly defined.

Q4: Are there alternative correction formulas?
A: Yes, other formulas include Fridericia's (QTc = QT/RR^1/3) and Framingham (QTc = QT + 0.154(1-RR)), though Bazett's remains most commonly used.

Q5: When should QTc monitoring be performed?
A: Before and during treatment with QT-prolonging medications, in patients with syncope or family history of sudden death, and in congenital long QT syndrome.