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'''There are three simple methods to determine the hart frquency (HF):''' | '''There are three simple methods to determine the hart frquency (HF):''' | ||
# Count the small (1mm) lines between two QRS-complexes. Hens, the ECG paper runs with 25 mm/sec through the ECG writer, therefore: [[Afbeelding:HFformule.png]]This method work fine in case of tacycardia (>100 beats/minute)<br> | # Count the small (1mm) lines between two QRS-complexes. Hens, the ECG paper runs with 25 mm/sec through the ECG writer, therefore: [[Afbeelding:HFformule.png]]This method work fine in case of tacycardia (>100 beats/minute)<br> | ||
# To determine the frequency of a normal sinus ritme: Use the sequence 300-150-100-75-60-50-43-37. Count from the first QRS complex, the first thick line is 300, the next line 150 etc. Stop the sequence at the next QRS complex. When the second QRS complex is in between two lines, take the mean of the two numbers from the sequence. You can finetune this method with the following more precise sequence: *'''300'''''-250-214-187-167-'''''150''' | # To determine the frequency of a normal sinus ritme: Use the sequence 300-150-100-75-60-50-43-37. Count from the first QRS complex, the first thick line is 300, the next line 150 etc. Stop the sequence at the next QRS complex. When the second QRS complex is in between two lines, take the mean of the two numbers from the sequence. You can finetune this method with the following more precise sequence: | ||
*'''300'''''-250-214-187-167-'''''150''' | |||
*'''150'''''-136-125-115-107-'''''100''' | *'''150'''''-136-125-115-107-'''''100''' | ||
*'''100'''''-94-88-83-79-'''''75''' | *'''100'''''-94-88-83-79-'''''75''' | ||
*'''75'''''-71-68-65-62-'''''60''' | *'''75'''''-71-68-65-62-'''''60''' | ||
# Non regular ritmes are best determined with the "3 second marker method" Count the number of QRS-complexes that fitt in 3 seconds (some ECG writers register this period on the ECG paper. Multiply this number by 20 and find the number of beats/minute. | |||
# Non regular ritmes are best determined with the "3 second marker method" Count the number of QRS-complexes that fitt in 3 seconds (some ECG writers register this period on the ECG paper). Multiply this number by 20 and find the number of beats/minute. | |||
{{clr}} | {{clr}} | ||
== | ==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) | ||
** Het | ** Het parasympathic system (nervus vagus) e.g. acetycholin decreases the frequency and atrioventricular conduction. The parasympathic system effects mainly the atria. | ||
* De | * De filling of the heart. Cardiac filling increases the frequency. |