|«Step 1: Rhythm||Step 3:Conduction intervals (PQ, QRS, QT, QTc)»|
What is the heart rate? To answer this question, determine the time between two QRS complexes. Previously, the ECG was registered on a paperstrip transported through an ECG writer at the speed of 25 mm/second. Nowadays, digital ECG registration is common however, the method of determining the frequency remains the same. The ECG paper has a grid with thick lines 5 mm apart (= 0,20 second) and thin lines 1 mm (0,04 second).
|There are three simple methods to determine the heart rate (HR)|
What changes the frequency of the heart?
A number of factors change the heart frequency including:
- the (para) sympathic nerve system.
- The sympathic system e.g. epinephrin (=adrenalin) increases the atrioventricular conduction and contractility. (the fight, fright, flight reaction)
- The parasympathic system (nervus vagus) e.g. acetycholin decreases the frequency and atrioventricular conduction. The parasympathic system effects mainly the atria.
- Cardiac filling increases the frequency.
- Also arrhythmias influence heart rate.