**4.1 Heart rate**

Athlete human beings and athlete dogs have mean HR and maximum HR lower than sedentary individuals, the physical activity modulates the sinus node causing decrease of the average of these HR (Cavalcanti et al., 2009, Martinelli et al., 2005), and increasing HR variability and the average RR interval. Endurance exercise training has been established to alter autonomic nervous system activity, resulting in an apparent increase in cardiac parasympathetic tone coupled with decreases in sympathetic activity. For example, in both humans and animals, the heart rate at submaximal workloads was reduced in trained individuals compared with sedentary controls (Smith et al., 1989). A resting bradycardia is a well-established consequence of exercise training and is, in fact, used as a marker that the exercise-trained state has been achieved. Both acetylcholine content and cholineacetyl transferase were increased in the hearts of trained rats compared with control rats (DeSchryver and Mertens-Strythaggen, 1975).

The circadian variation in HR is similar to that illustrated in Figure 2. Obviously, the limits of the upper and lower HR should be calibrated in the software, according to the animal being studied.

In the thoracic region, where the adhesive electrodes are positioned, there must be ample shaving, cleaning of the area with alcohol to remove the hair and skin oils. After the gel electrodes are fixed with adhesive tape, dry the skin (Figure 1) and it should be held with a

There is the possibility of performing the examination without the use of waistcoat only conditioning the device with bandage. After placing the recording monitor, cervical or Elizabethan collar should be used to prevent dog bites and damages to the unit. In the literature, the use of cervical or Elizabethan collars did not influence the heart rate in healthy dogs (Cavalcanti et al., 2007). However, it is clear that some dogs tolerate the use of cervical

The weight of the device and the size of the vest should be compatible with the size of the

Every animal should have a sheet of notes taken during the activities along the course of the recording. It should be noted that the starting time of the examination correlates with the observed daily heart rate (HR) and, possibly, arrhythmias. The report should contain the results of the exam starting time, duration of the examination, the level of recording quality, the maximum, average and minimum HR in each hour and the same HR data on the total examination time. Some supraventricular and ventricular premature complexes may occur in healthy dogs and cats, and in humans these premature complexes increased with age. Atrioventricular blocks of first or second degrees may also occur in healthy dogs. Variations and changes unique to the T wave are not considered diagnostic of CE in small animals.

Athlete human beings and athlete dogs have mean HR and maximum HR lower than sedentary individuals, the physical activity modulates the sinus node causing decrease of the average of these HR (Cavalcanti et al., 2009, Martinelli et al., 2005), and increasing HR variability and the average RR interval. Endurance exercise training has been established to alter autonomic nervous system activity, resulting in an apparent increase in cardiac parasympathetic tone coupled with decreases in sympathetic activity. For example, in both humans and animals, the heart rate at submaximal workloads was reduced in trained individuals compared with sedentary controls (Smith et al., 1989). A resting bradycardia is a well-established consequence of exercise training and is, in fact, used as a marker that the exercise-trained state has been achieved. Both acetylcholine content and cholineacetyl transferase were increased in the hearts of trained rats compared with control rats

The circadian variation in HR is similar to that illustrated in Figure 2. Obviously, the limits of the upper and lower HR should be calibrated in the software, according to the animal

Later, you put on a denim jacket or something similar, which will remain on the animal during the exam. The CE device will be packaged in the side pocket of the jacket and the

protective bandage to prevent the electrodes to come off.

cables will remain protected (Figure 1).

collar better than the Elizabethan one.

animal; cats should use smaller devices

**4. The result of the examination** 

(DeSchryver and Mertens-Strythaggen, 1975).

**4.1 Heart rate** 

being studied.

Fig. 2. Graphics show the average of the mean HR at different times of day, observed in sedentary (S) and athlete (A) dogs of the German shepherd breed. Note that the two groups of dog exhibit the same trend to increase and decrease in mean HR over 24 hours, and lower heart rates were observed from three to six hours of the morning.

#### **4.2 Indication of the CE to evaluate clinical signs related to arrhythmias**

Monitoring with the CE for 24 hours is especially useful because it provides details of the patient's heart rhythm, the total number and type of abnormal complexes, as well as the specific time of the day when they occurred. The clinician can assess the animal's activities in the period of recording and correlate exam results with clinical signs manifested at every moment.

The method of CE does the ECG recording for long periods and during the patient's daily activities. This allows us to observe spontaneous changes and those caused by activities or situations experienced by the patient's daily routine and, above all, make sure that the reported symptom related to whether or not an electrocardiographic changes. Symptoms that may be caused by changes in heart rhythm should occur often enough to be surprised while doing the recording of the ECG; however, the direct relationship is not always present and can have situations like:


In the situation "a" it is impossible to establish any relationship and the examination should be repeated depending on the severity of the clinical suspicion, in "b", though symptoms do not occur, the type of arrhythmia observed may suggest a possible correlation with the sign mentioned above; in "c", discards the possibility of a relationship of symptoms with arrhythmia and another cause should be investigated, in "d", each case must be individualized, because we have patients that fall in both "b" and "c".

#### **4.3 Supraventricular arrhythmias**

The CE detects the same supraventricular arrhythmias than the ECG, however there are some considerations to be taken.

Continuous Electrocardiography in Dogs and Cats 147

Less than 50 May be the initial DCM, annual reassessment

More than 100 Likely to be suffering from DCM, revaluation of 3

Between 50 and 100 Suspect animal, revaluation every three to six

Table 1. Recommendations for interpretation of CE exam in Doberman dogs (Goodwin, 1998). Sudden death has been reported in young dogs of German shepherd breed, very similar to the illness of sudden death in human babies. Both are characterized by paroxysmal ventricular tachycardia at moments of parasympathetic influences, as in deep sleep and after exercise. Any animal displaying episodes of ventricular tachycardia has high risk of

This familiar arrhythmia in German shepherd dogs usually decreases after seven months of age, but can be detected in animals older than 5 years and are considered affected, the animals showing more than 240 PVC during the examination. Death was observed in 15 to 20% of affected animals and usually occurs at the age of 4-8 months (Moise et al., 1997). In Brazil, there are no reports of this hereditary disease that has been observed in North

The study of myocardial ischemia by CE was made possible by technical advances in recording systems, with enhancements to the registry of the ST segment. As the ST as a sign of low frequency response, its correct detection and registration will depend on the frequency range of recorders, which should be between 0.05 and 100 Hz. The analysis system should be able to do it automatically, exposing the behavior of the ST segment graphically in time function, with the possibility of observation and interaction of events by the analyst. In general, the electrocardiogram is superior to CE in detecting myocardial

In veterinary medicine, myocardial ischemia due to obstruction of large coronary vessels is uncommon and ST segment changes may occur in cases of hypertrophic left ventricle due to obstruction of small vessels. No healthy dogs of the Boxer, English cocker spaniel, Doberman and German shepherd breeds have shown significant change in the ST segment. The ventricular arrhythmia is a common consequence of myocardial infarction and is easily identified and quantified in dogs with induced myocardial infarction and examined by CE. Moreover, it is known that at the time of greatest oxygen demand of the heart muscle (e.g. during exercise, stress ECG) ST changes are best identified in humans and the same occurs in dogs subjected to experimental infarction and evaluated by CE, moreover, the CE has a

higher ability to detect small myocardial infarction in dogs than the resting ECG.

**4.6 CE Indication for detection of myocardial ischemia** 

ischemia due to greater number of variations of electrode placement.

Annual reassessment of the CE, if the animal is of a predisposed family

required.

months.

to 6 months.

complexes in 24 hours Interpretation

Frequency of premature ventricular

None

sudden death.

America.

The presence of supraventricular arrhythmias is typically observed in less than 25% of healthy small animals within 24 hours. The evaluation of this type of arrhythmia should be cautious; the software which reads the tapes are calibrated to values of human waves and sinus arrhythmia of normal dogs may be misinterpreted as supraventricular premature complex, and even if there are trembling in the baseline sinus, arrhythmia associated with the software can be interpreted incorrectly, such as atrial fibrillation. Solid memory devices (e.g. Memory card) work similarly to cassette and offer the advantage to be programmed to work with range of values of dogs and cats ranges, minimizing the number of premature supraventricular complexes false positive in the exam. So when the reading is done, someone familiar with sinus arrhythmia of dogs must be present to review this arrhythmia.
