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!Use a calculator | !Use a calculator | ||
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| Count the small (1mm) squares between two QRS complexes. | | Count the small (1mm) squares between two QRS complexes. The ECG paper runs at 25 mm/sec through the ECG printer; therefore:[[Image:HFformule_en.png|none]]This method works well in case of tachycardia (>100 beats/minute)<br> | ||
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Non-regular rhythms are best determined with the "3 second marker method" Count the number of QRS complexes that fit into 3 seconds (some ECG writers register this period on the ECG paper). Multiply this number by 20 to find the number of beats/minute. | Non-regular rhythms are best determined with the "3 second marker method". Count the number of QRS complexes that fit into 3 seconds (some ECG writers register this period on the ECG paper). Multiply this number by 20 to find the number of beats/minute. | ||
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==What changes the frequency of the heart?== | ==What changes the frequency of the heart?== | ||
A number of factors change the heart frequency including: | A number of factors change the heart frequency, including: | ||
* the (para) sympathic | * the (para) sympathic nervous system. | ||
** The '''sympathic system''', e.g. epinephrine, (=adrenalin) increases atrioventricular conduction and contractility. (the ''fight | ** The '''sympathic system''', e.g. epinephrine, (=adrenalin) increases atrioventricular conduction and contractility. (the ''fight or flight'' reaction) | ||
** The parasympathic system (nervus vagus,) e.g. acetycholine, decreases the frequency and atrioventricular conduction. The parasympathic system affects mainly the atria. | ** The parasympathic system (nervus vagus,) e.g. acetycholine, decreases the frequency and atrioventricular conduction. The parasympathic system affects mainly the atria. | ||
* Cardiac filling increases the frequency. | * Cardiac filling increases the frequency. | ||