Question

To determine the Q-T interval, measure the interval between two consecutive R waves (R-R interval). If the measured Q-T interval is less than half the R-R interval of that QRS complex and the R wave of the following complex, it is probably normal (provided the patient's heart rate is 95 beats/min or less). Alternatively, count the number of small boxes between the beginning of the QRS complex and the end of the T wave. Then multiply that number by 0.04 second. What is the method used to determine the Q-T interval?

1) Measuring the interval between two consecutive R waves
2) Dividing the measured Q-T interval by the R-R interval
3) Counting the number of small boxes between the QRS complex and the T wave
4) Multiplying the number of small boxes by 0.04 second

Answer 1

The QT interval on an ECG is determined by counting the number of small boxes between the start of the QRS complex and the end of the T wave and then multiplying that count by 0.04 seconds. Comparing this measurement to half the R-R interval helps ascertain normalcy if the heart rate is 95 bpm or less.

Step-by-step explanation:

The method used to determine the QT interval involves several steps. Firstly, count the number of small boxes between the beginning of the QRS complex and the end of the T wave. Secondly, multiply the number of small boxes by 0.04 seconds to get the duration of the QT interval. The initial step of counting the boxes correlates to counting the duration between specific points of the electrocardiogram (ECG). Multiplication by 0.04 seconds converts this count into time, as each small box represents 0.04 seconds on standard ECG paper.

To check for normality, one may compare the measured QT interval to half of the R-R interval (the time between two consecutive R waves). If the QT interval is less than half of the R-R interval, and the patient's heart rate is 95 beats/min or less, the QT interval can be considered probably normal. This comparison helps in assessing whether the depolarization and repolarization of the ventricles is occurring within a typical duration relative to the entire cardiac cycle.