Final answer:
Narrow complex tachycardia has a QRS complex that measures less than 120 milliseconds, and this complex represents the rapid electrical signal that causes the ventricles to contract. Conditions like ventricular tachycardia may alter the shape of the QRS complex, but in narrow complex tachycardia, it remains within normal dimensions. Other related ECG patterns include the second-degree block with irregular P to QRS pattern and third-degree blocks showing no P to QRS correlation.
Step-by-step explanation:
In narrow complex tachycardia, the QRS complex typically measures less than 120 milliseconds. The QRS complex in the electrocardiogram (ECG) represents the depolarization of the ventricles, which is the rapid firing electrical signal that leads to ventricular contraction. The time span and shape of the QRS complex can be influenced by the electrical pathway and shape of the heart. In conditions such as ventricular tachycardia, the QRS complex might be abnormally shaped, but in narrow complex tachycardia, the shape remains within normal dimensions. Systolic blood pressure usually peaks shortly after the QRS complex, indicating ventricular contraction.
A second-degree block might show a pattern where only half of the P waves are followed by a QRS complex, while in atrial fibrillation, there is an increased frequency of QRS complexes without a normal preceding electrical pattern. A third-degree block, also known as a complete heart block, displays no correlation between the P wave and the QRS complex.
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