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

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 ischemia due to greater number of variations of electrode placement.

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.

Continuous Electrocardiography in Dogs and Cats 149

Human beings studies of HR variability in the spectral domain have shown that the spectral power contained in certain frequency bands reflects, in part, the sympathetic and parasympathetic modulation of sinus node activity. Studies using selective autonomic blockade have shown that power in the frequencies of HR variability > 0.15 Hz can be attributed to parasympathetic modulation, whereas power in frequencies < 0.15 Hz are related to both sympathetic and parasympathetic modulation, thus spectral analyses of HR variability have been used in a variety of settings and pathologies to assess autonomic modulation. Rapid changes in sympathovagal control are known to occur in the setting of exercise and recovery from exercise. Exercise is characterized by a decrease in parasympathetic tone and an increase in sympathetic tone, resulting in an increase in heart rate. During recovery from exercise, HR gradually decreases as parasympathetic tone

In human medicine the variability of RR intervals provides useful information in defining patient prognosis after acute myocardial infarction, in the person with DCM, as well as to stratify the risk of sudden death in diabetic patients. it is known that the variability decreases in the presence of heart failure in dogs with chronic myxomatous mitral valve (Crosara et al., 2010) and in advanced DCM (Calvert and Wall, 2001), and a study of HR variability in cats has not been found yet. Perhaps with more studies, HR variability will be

Calvert, C. A.; Jacobs, G. J.; Smith, D. D.; Rathbun, S. L.; Pickus, C. W. Association between

Calvert, C. A.; Pickus, C.W.; Jacobs, G. J. Efficacy and toxicity of tocainide for the treatment of

Calvert, C. A.; Wall, M. Effect of severity of myocardial failure on heart rate variability in

Cavalcanti, G. A. de O.; Nogueira, R. B.; Gonçalves, R.S. ; Araujo, R. B. ; Muzzi, R. A. L.;

Cavalcanti, G. A. O.; Nogueira, R. B.; Sampaio, G. R.; Araujo, R. B.; Gonçalves, R.S. Avaliação

Crosara, S.; Borgarelli, M.; Perego, M.; Häggström, J.; LA Rosa, G.; Tarducci, A.; Santilli, R.

Dae, M. W.; Lee, R. J.; Ursell, P. C. ; Chin, M.C.; Stillson, C. A.; Moise, S. Heterogeneous

*Journal of Veterinary Internal Medicine*, v.4, n. 10, p.235-240, 1996.

*Veterinary Association*, v.216, n. 1, p.34-39, 2000.

*Ciências da Vida*, v. 27, p. 461-463, 2007.

*Veterinary Journal*, v. 88, n. 10, p. 386-392, 2010.

results of ambulatory electrocardiography and development of cardiomyopathy during long-term follow-up of Doberman pinchers. *Journal of the American* 

ventricular tachyarrhythmias in Doberman pinschers with occult cardiomyopathy.

Doberman pinschers with and without echocardiographic evidence of dilated cardiomyopathy. *Journal of the American Veterinary Medical Association*, v.219, n. 8,

Sampaio, G. R. Influência da utilização de colar elizabetano ou colar cervical em cães submetidos a eletrocardiografia contínua (Holter). *Revista Universidade Rural. Série* 

por eletrocardiografia contínua (holter) em cães da raça Pastor Alemão praticantes de atividade física regular. *Arquivo Brasileiro de Medicina Veterinária e Zootecnia*, v.

A. Holter monitoring in 36 dogs with myxomatous mitral valve disease. *Australian* 

Sympathetic Innervation in German Shepherd Dogs With Inherited Ventricular Arrhythmia and Sudden Cardiac Death. *Circulation*, v. 96, n. 4, p. 1337-1342, 1997.

returns and sympathetic tone withdraws.

more used in Veterinary Medicine

p.1084-1088, 2001.

61, p. 1446-1449, 2009.

**5. References** 

The ST segment analysis by electrocardiography is inadequate when there is left bundle branch block or Wolff-Parkinson-White syndrome or QRS complex with very low amplitude. Moreover, in large variations in the morphology of the QRS complex, the ST segment assessment should be undertaken with caution, even if it is caused by change of posture. It is noteworthy that a normal examination does not exclude ischemic heart disease, even by the natural variability of ischemic injury.
