1. What is QT Interval?

The QT interval represents the total time from ventricular depolarization to complete repolarization on an ECG. It's measured from the beginning of the QRS complex to the end of the T wave.

2. How Does the Calculator Work?

The calculator uses the QT interval formula:

Where:

• Small Boxes — 1 mm squares on ECG paper
• 40 — Conversion factor (ms per small box at 25 mm/s paper speed)

Explanation: At standard ECG paper speed of 25 mm/s, each small box (1 mm) represents 40 ms of time.

3. Importance of QT Interval Calculation

Details: Accurate QT interval measurement is crucial for detecting prolonged QT syndrome, which can lead to dangerous arrhythmias and sudden cardiac death.

4. Using the Calculator

Tips: Count the number of small boxes from Q start to T end on ECG paper. Enter the number of boxes to calculate the QT interval in milliseconds.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal QT interval?
A: Normal QT interval is typically 350-440 ms for men and 360-460 ms for women, but varies with heart rate.

Q2: How does heart rate affect QT interval?
A: QT interval shortens with increasing heart rate. Various correction formulas (Bazett, Fridericia) exist to account for this.

Q3: When should QT interval be measured?
A: QT interval should be measured in leads where the T wave is clearly defined, typically leads II or V5.

Q4: What causes prolonged QT interval?
A: Causes include congenital long QT syndrome, medications, electrolyte imbalances, and myocardial ischemia.

Q5: How accurate is manual QT measurement?
A: Manual measurement has some inter-observer variability. For critical decisions, automated measurements or expert consensus may be preferred.