**4.8 Heart rate variability**

Several types of analysis of the variability of intervals between R waves are provided by the examination. The RR variability is a way to evaluate the cardiac autonomic system functioning, and high variability of RR indicates a good heart function.

The analysis of HR variability is achieved through the study of parameters for time domain and frequency, provided directly by the computer analysis program. Although there are certain parameters in the time domain that can be analyzed by the ECG, the best method for this analysis is the CE, because this evaluation is made considering more data and obtains more consistent results.

The following variables are evaluated in the time domain: mean NN (mean of all normal RR intervals of the exam), SDNN (standard deviation of all normal sinus R-R intervals), SDANN (standard deviation of the averaged normal sinus R-R intervals for all 5-minute segments of the entire recording), SDNN index (mean of the standard deviations of all normal R-R intervals for all 5-minute segments of the entire recording), rMSSD (root mean square of the sum of squared difference of adjacent normal RR intervals throughout the exam) and pNN50 (the percentage of adjacent R-R intervals that varied by more than 50 ms).

In the frequency domain, the following variables are assessed: HF (high frequency), which comprises 0.15 to 0.4 Hz or 2.5 to 6.6 s / cycle; LF (low frequency), consisting of 0.0033 to 0.04 Hz or 5min/ciclo the 25s, ULF (ultra low frequency), which includes values less than 0.0033 Hz, and the ratio between the LF and HF components (LF / HF).

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 returns and sympathetic tone withdraws.

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 more used in Veterinary Medicine

#### **5. References**

148 A Bird's-Eye View of Veterinary Medicine

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,

The diagnosis of cardiac arrhythmias and evaluation of therapeutic results requires prolonged observation of the ECG; in addition, the long-term ECG enables clarity of paroxysmal symptoms that may occur after a therapeutic procedure. The aggravation of preexisting arrhythmias or the emergence of new arrhythmias (proarrhythmia) is a phenomenon that can occur during treatment, especially the drug induced treatment, and the CE exam can provide information, even in asymptomatic cases. The CE should not be routinely done in the monitoring of patients with artificial pacemakers; however, it constitutes a powerful tool in the elucidation of paroxysmal symptoms in this group of

In veterinary medicine, it is considered efficient the drug that causes a decrease of at least 70% in the number of premature supraventricular complexes. In dogs of the Doberman breed with DCM and treated with tocainamida, the total number of CVPs decreased between 70 and 80%, and the ventricular tachycardia 90%, which can be defined as

Several types of analysis of the variability of intervals between R waves are provided by the examination. The RR variability is a way to evaluate the cardiac autonomic system

The analysis of HR variability is achieved through the study of parameters for time domain and frequency, provided directly by the computer analysis program. Although there are certain parameters in the time domain that can be analyzed by the ECG, the best method for this analysis is the CE, because this evaluation is made considering more data and obtains

The following variables are evaluated in the time domain: mean NN (mean of all normal RR intervals of the exam), SDNN (standard deviation of all normal sinus R-R intervals), SDANN (standard deviation of the averaged normal sinus R-R intervals for all 5-minute segments of the entire recording), SDNN index (mean of the standard deviations of all normal R-R intervals for all 5-minute segments of the entire recording), rMSSD (root mean square of the sum of squared difference of adjacent normal RR intervals throughout the exam) and pNN50 (the percentage of adjacent R-R intervals that varied by more than 50 ms). In the frequency domain, the following variables are assessed: HF (high frequency), which comprises 0.15 to 0.4 Hz or 2.5 to 6.6 s / cycle; LF (low frequency), consisting of 0.0033 to 0.04 Hz or 5min/ciclo the 25s, ULF (ultra low frequency), which includes values less than

therapeutic success in the treatment of DCM in PVC (Calvert et al., 1996).

functioning, and high variability of RR indicates a good heart function.

0.0033 Hz, and the ratio between the LF and HF components (LF / HF).

even by the natural variability of ischemic injury.

patients.

**4.8 Heart rate variability** 

more consistent results.

**4.7 Evaluation of therapeutic procedures results** 


**9** 

*Brazil* 

**Arthroscopic Follow-Up After** 

Cleuza Maria de Faria Rezende,

*Escola de Veterinária – UFMG,* 

**Rupture of the Cranial Cruciateligament** 

The femoro-patellar-tibial joint is one of the most complex, with different structures that, altogether, keep the joint stability and functionality (Cook, 2010; de Rooster et al., 2010, Pozzi & Kim, 2010). Due to its big functional demand, the cranial cruciate ligament (CrCL) is the structure most frequently injured. The rupture of this ligament is of the most common causes of lameness in the dog and the resulting instability leads to the development of degenerative joint disease (DJD). Still today, the search for the ideal technique to treat CrCL rupture, with joint stabilization and prevention or minimization of DJD, persists. However, would joint stabilization be the only factor to be considered for the treatment of CrCL rupture and its sequels? Won't the effects of instability on the other structures deserve more investigation? Would the inflammatory response mediators be responsible for the looseness of the intra-articular graft or is it exclusively due to improper fixation or inadequate post-

According to literature, the joint degeneration process starts as soon as seven days after CrCL rupture and, at Day 21, signals suggesting osteoarthritis can be radiographically examined. In arthroscopic evaluation, however, lesions are already significant and

Arthroscopy is a minimally invasive exam, with minimal morbidity, which allows complete visualization of structures with magnification of images and precise diagnosis of the articular condition in its natural environment. The minimal morbidity enables periodic joint evaluations (Van Ryssen & Van Bree, 1998; Hulse et al., 2010; Goldhammer et al., 2010), what permits to monitor the lesion ( Borges, 2006; Bleedorn et al., 2011) and the treatment evolution (Case et al., 2008), allowing the articular function prognosis

Arthroscopy can be employed for evaluating and defining the DJD staging. It gives the surgeon a better understanding of the joint degeneration process, the most prevailing

The arthroscopy had a significant impact especially in our clinical practice in what concerns diagnosis and treatment of articular alterations in the dog. Non-specific arthritis,

**1. Introduction** 

operatory?

characteristic in this period.

(Ljungvall & Ronéus, 2011).

condition among all diseases in the dog.

Eliane Gonçalves de Melo and Natalie Ferreira Borges

