Cardiac Recovery Index
This parameter is finding very good application as a means of determining the fitness of horses to continue in an endurance or competitive riding event. It also has value to the individual in a training program to determine whether a horse is handling the applied level of stress, and when he is ready for further progress.
Experienced veterinarians have long recognized the setting of "fixed" pulse recoveries at check points leaves much to be desired. We know that often a given horse with a pulse of 72 may be more metabolically fit to continue than another with a pulse of 64. A single pulse measurement can not assess cardiovascular response. With the advent of onboard monitors, several things became apparent. First, there is a very rapid decline in heart rate in the fit horse after cessation of exercise. Typically, a fit horse with an "onboard" monitored heart rate will show a working rate of 120 to 160 beats per minute. By the time one can dismount and take the heart rate with a stethoscope, it will have dropped 30 to 50 percent. Thus, it is reasonable to predict that by the time a fit horse could be presented to a P/R team at a check point, it would have a heart rate of 60 to 80 beats per minute.
Next, with the use of an onboard monitor, it became evident that if you trotted a fit horse a short distance (250 feet), the heart rate would rise approximately 50 to 75 percent. Within approximately 30 seconds of conclusion of the trot out, the pulse would return to the pre-trot out rate or lower.
1. The horse is presented when it is at or below the maximum designated pulse for that check point. If the parameter is used at a "gate into a hold," the horse may be presented anytime within the hold period (as long as it is not above the maximum designated pulse). It is strongly advised that all horses should be presented within 30 minutes of arrival at any check point, regardless of the type of check used.
2. A 15 second pulse count is then taken by the examining veterinarian.
3. The horse is then briskly trotted out 125 feet and back 125 feet. A total of 250 feet. Time is started at commencement of the trot out.
4. One minute later, the pulse or heart rate is again taken.
5. To be allowed to continue, the heart rate must return to the pre-trot out level or lower.
Time is started at the commencement of the trot out because of the inherent variability in the pace of the trot out. Those who trot less briskly have less recovery time before the second pulse is taken.
During the time the horse is trotting, the examining veterinarian is evaluating the horse for soundness, willingness and coordination. It takes most horses about 25 seconds to complete the trot out. This allows an efficient veterinarian adequate time to evaluate the other parameters such as muscous membranes, capillary refill and hydration before taking the second pulse. Thus an exam need only take a minute and a half per horse.
Even horses presenting in the "normal pulse ranges" tend to show full recovery to the pre-trot out value. However, as with any criteria, judgment needs to be utilized. If the values are in the normal range, e.g. less than 56 bpm, one can allow a leeway of one count in 15 seconds. Recognize, it is also easy to miscount one beat in a 15 second count. Above 60 beats per minute, however, tend to be more critical. This is especially true if other parameters are questionable. If all other parameters are excellent, you would likely release the horse. If not, you may want to set this horse aside and recheck in another five minutes. Really know you want to send this horse on!
Horses with imminent muscle problems (such as exertional rhabdomyolysis) often exhibit a poor recovery index significantly in advance of other clinical signs. Thus, if there is a question, it is advisable to recheck the horse in about five minutes. The index also picks up some instances where lameness is imminent, since pain elevates heart rate.
One also needs to consider horses that are hyper-exciteable. Nearly always the "hyper" horse will also return to pre-trot out levels. If he does not do so and everything else checks out excellently, simply recognize what is happening and ignore this one criteria.
Experience has shown that horses not showing recovery within 30 minutes have a poor completion rate. Therefore, any rechecks allowed should fall within 30 minutes of initial presentation.
One should recognize that this parameter may not be needed on every horse early in the ride. For example, at a first check point or a crowded check point, one may choose to utilize it only on questionable cases.
The criteria is best applied at check points where there is a "gate into a hold." This allows the most rider and veterinary flexibility. For example, it allows the rider to best manage his individual horse as to feeding, watering, massaging, etc. before presenting or after presenting. It also helps assure that those riders who timed into the P/R at the same time will get out of the check point at the same time.
Used properly and with good judgment, this parameter is very effective in objectively defining those horses who should not be allowed to continue.
By Kerry J. Ridgway, DVM
Endurance News, May 1988
YouTube clip of taking a horse's pulse Click