Queensland News - Australian Veterinary Association

AVA Queensland News - August 2009Continued from pg. 16Heart rateIf rhythm is regular, use:Divide 3000 by the number of small boxes (each represents 20 ms at a 50 mm/sec paper speed) within theR-R interval (or 1500 divided by number of small boxes if using the 25 mm/sec paper speed) (see Figure 1)Or use a heart rate calculator ruler.If rhythm is irregular:Count how many complexes (or R-R cycles) occur within a 6 or 10 second time frame as marked on thepaper. e.g. 9 complexes in 6 seconds, multiply this number by 10 (ie 6s x 10 = one minute) to calculate therate per minute (e.g. 9 x 10 = 90 bpm).Heart rhythmGeneral inspection:Is it a normal sinus rhythm? Are any deviations from normal occurring in a repetitive sequence? (e.g.respiratory sinus arrhythmia); are they occasional, frequent or continuous? Regular (some forms of ventriculartachycardia) or irregular (e.g. atrial fibrillation).P wave identification:Are they present, are they regular or irregular?QRS complex recognition:Are all QRS complexes uniform in appearance? Are they likely to be ectopic ventricular complexes (wideand bizarre) in origin or are they derived from a supraventricular mechanism (normal in appearance)?Figure 1: Normal canine P-QRS-T complex.Time intervals areas for a paper speed of 50 mm/sec.Amplitude as for 1 cm= 1 mVRelationship between P wave and QRS complexes:Usually a long lead II rhythm strip is used. Use calipers or a card with marks placed on it to record the durationof P-P wave intervals, P-QRS intervals, and QRS-QRS intervals for evidence of rhythm abnormalities.Measuring Complexes and IntervalsUse the lead II rhythm strip.Measurements are made in terms of width or interval length measured in milliseconds (ms) or seconds (sec)by measuring the number of small boxes, with each box measuring 20 ms (or 0.02 sec) at a paper speed of50 mm/sec.17