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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 print this period on the ECG paper). Multiply this number by 20 to find the number of beats/minute.
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A number of factors change the heart frequency, including:
A number of factors change the heart frequency, including:
* the (para) sympathic nervous system.  
* the (para) sympathic nervous system.  
** The '''sympathic system''', e.g. epinephrine, (=adrenalin) increases atrioventricular conduction and contractility. (the ''fight or flight'' reaction)
** 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.
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