**2.5 Methods of ECG and ECG machine**

Bipolar lead systems (Base apex I, II, III and X, Y and Z of the orthogonal system) and Unipolar leads (aVF, aVR, aVL and thoracic) have been described in animals. In large animals for the detection of cardiac arrhythmias base lead II and Y lead of the orthogonal system are most commonly used [9].

In cattle, ECG examinations method followed is base apex limb lead II. After adequate rest, the animal is kept in standing position in a trevis. ECG gel is applied on the lead attachment sites. Three sites are selected for application of the clips (**Figure 1**). Positive lead I is attached between the 3rd-5th intercostal space on the left side behind the elbow. Negative lead II is attached to the caudal 1/3rd of the jugular furrow and neutral lead III is attached away from the other two leads at the wither point [11].

The ECG machine is simply a voltmeter or galvanometer that records the changes in the electrical potentials occurring during each cardiac cycle. These changes are recorded on an ECG paper with a grid by a stylus. The stylus gets deflected according to the intensity of the electrical activity. The ECG machine is connected to a monitor and has an inbuilt printer. The results are obtained almost immediately. The clip used in ECG examinations is called an alligator clips. These clips have a pointed mouth with serrated ends for firm holding of the thick cattle skin. The serrated ends are very sharp and hence before usage it should be rasped or blunted to prevent injury to the animals. Before application of the alligator clips the sites should be cleaned with surgical spirit and adequate ECG gel should be applied for better contact.

#### **Figure 1.**

*Positive lead I attached at the 3rd-5th intercostal space. Negative lead II attached at the caudal 1/3rd of the jugular furrow. Neutral lead III attached away from the first two leads at the point of withers.*

#### **2.6 Guidelines for reading the ECG**

The ECG machine is equipped with a printer that generates a graphical representation on gridded paper of the electrical activity of the heart. The speed of the paper is set at 25 mm/second and the stylus present in the ECG records the deflection produced by the electrical impulses. The vertical axis of the grid denotes the voltage and direction of the deflection, either positive or negative, with respect to the baseline. The horizontal axis represents the time taken for each event in the cardiac cycle as well their sequence. The ECG paper is composed of a grid with small and large boxes. Each small box on the horizontal axis corresponds to a 0.04 second interval. Five small boxes form a large box which consequently represents 0.2 seconds. On the vertical axis, each small box corresponds to 0.1 mV.

#### **2.7 ECG graph and its Normal waves**

An ECG gives a graphical representation of the electrical changes occurring in the heart as a P-QRS-T complex. The electrical depolarization starting at the SA node travels across the atria creating a brief upward deflection of the stylus forming the P wave, representing atrial depolarization. The P-R interval is formed when the depolarization passes from the SA node to the AV node and into the ventricular tissue. The ventricular septum is the first to get depolarized in a direction away from the positive electrode creating a small negative deflection called the Q wave. A large positive/negative deflection, termed R wave, is created when the bulk of the ventricular myocardium gets depolarized. The S wave is formed when the remaining basilar portion of the ventricles gets depolarized. Thus the ORS complex is representative of ventricular depolarization. Complete ventricular depolarization is followed by repolarization before the next cardiac cycle. There is a difference in repolarization of the ventricular tissue creating a potential difference across the ventricular myocardium which forms the T wave.

The normal P wave amplitude and duration in Holstein cattle is 0.05–0.32 mV and 0.05–0.12 seconds respectively (**Figure 2**). In cattle, the QR and QS amplitudes are recorded separately and the normal values are 0.05–0.95 mV and 0.9–1-1 mV

**Figure 2.** *Normal ECG pattern in cattle.*

*Electrocardiogram and Its Interpretation of Cardiac Diseases in Cattle DOI: http://dx.doi.org/10.5772/intechopen.105042*


#### **Table 1.**

*Normal ECG values in cattle.*

respectively. The normal duration of the QRS complex is 0.04–1.0 seconds. The P-R interval and Q-T interval in normal Holstein cattle was found to be 0.12–0.26 seconds and 0.22–0.48 seconds respectively. In large animals, the T wave is more variable than in small animals and is generally not relevant in the detection of cardiac problems. The normal T wave amplitude and duration are 0.05–0.8 mV and 0.05–0.16 seconds respectively [10]. In **Table 1** the normal ECG values of cattle is given.

### **2.8 ECG graph and its interpretation**

Variations in an ECG from the normal values of amplitude and duration in the P-QRS-T complex is indicative of cardiac dysfunction. In general, an increase in the amplitude of the P wave is suggestive of right atrial enlargement and increase in duration of the P wave is seen in left atrial enlargement (**Figure 3**). The QRS complex in bovines is negative and an increase in amplitude of QRS complex and duration of Q-T interval is characteristic of ventricular hypertrophy (**Figure 3**). A positive S wave is indicative of myocardial infarction. Variations in T was may be helpful in the

#### **Figure 3.**

*ECG shows notching of P wave indicative of atrial enlargement and increase in amplitude of QRS complex and QT interval indicative of ventricular enlargement in cattle.*

**Figure 4.** *ECG shows sinus tachycardia in cattle.*

diagnosis of electrolyte and mineral imbalances. ECG alterations in some of the common cardiac diseases and electrolyte imbalances are described below.

Atrial fibrillation (AF) is occurs due to focal ectopic firing arising from within the pulmonary veins and spreading to the atria [12]. AF is the most common cardiac arrhythmia present in milking cows. 50% of the cows with AF were previously diagnosed with ketosis suggestive of a relationship between the two conditions [13]. ECG recording of AF reveals absence/decreased amplitude of the P wave with a series of rapid and irregular waves (F wave) on the base line. The QRS complex is normal in amplitude and duration but irregular [12]. In cattle, the heart rate exceeds 90 beats/ minute, it is called as sinus tachycardia (**Figure 4**) and if it is less than 47 beats/minute it is called as sinus bradycardia (**Figure 5**).

Endocarditis is an inflammatory disease affecting the layers of the endocardium in cattle due to bacterial infection. Bacterial endocarditis is most commonly of vegetative form (Healy, 1996). ECG examination in bovine vegetative endocarditis revealed deep QRS complex (1.7–2.5 mV) and tall T waves (0.8–1.5 mV) shown in the **Figure 6** [14].

Pericarditis is the inflammation of the pericardium with accumulation of serous or fibrinous inflammatory debris [15]. The most common cause of pericarditis in cattle is traumatic pericarditis [16] due to penetration of the pericardium by a hard foreign body. ECG taken in cattle affected with traumatic pericarditis shows decreased

**Figure 5.** *ECG shows sinus bradycardia in cattle.*

*Electrocardiogram and Its Interpretation of Cardiac Diseases in Cattle DOI: http://dx.doi.org/10.5772/intechopen.105042*

#### **Figure 6.**

*ECG shows deep QRS complex and tall T wave in cattle with endocarditis.*

#### **Figure 7.** *ECG shows regular alteration in P, QRS or T wave and elevation of ST interval in cattle with pericarditis.*

amplitude of QRS complex (<1.5 mV), regular alteration of P, QRS or T complexes and slurring/elevation in ST interval [17–19] shown in **Figure 7**.

In **Table 2**, ECG pattern of cattle with electrolyte and mineral imbalance was given. Hyperkalemia in an increase in potassium ion concentration in the blood caused by renal failure, severe dehydration and acidosis in calves with diarrhea [20]. The ECG in such animals shows wider QRS complex, tall T waves and deeper and higher S-T segment. A decrease in potassium ion concentration or hypokalemia occurs in case of inappetance, metabolic acidosis and increased excretion due to corticosteroid therapy combined with treatments used for ketosis [20]. The ECG recordings have tall and tent shaped T wave with an absence of P wave.

Hypocalcemia or parturient paresis is a condition common in periparturiant cattle due to deficiency of calcium characterized by progressive neuromuscular degeneration, circulatory collapse and depressed consciousness [21]. Hypocalcemia is a common finding in case of Milk fever, Downer cow syndrome, Creeper cows, etc. The ECG is has a characteristic prolonged Q-T interval and lengthened S-T segment (**Figure 8**). Cows with hypocalcemia may have arrhythmias and sometimes complete heart block. Hypercalcemia is an increase in the levels of serum calcium most commonly due to primary hyperparathyroidism and malignancy [22, 23] as well as over supplementation of calcium in treatment of milk fever. Hypercalcemia decreases the atrial activity and increases ventricular activity [24]. ECG reveals short Q-T interval,


**Table 2.**

*ECG patterns in cattle with electrolyte and mineral imbalance.*

*Clinical Use of Electrocardiogram*

*Electrocardiogram and Its Interpretation of Cardiac Diseases in Cattle DOI: http://dx.doi.org/10.5772/intechopen.105042*

#### **Figure 8.**

*ECG shows prolong QT interval and lengthened ST segment in cattle with hypocalcemia.*

#### **Figure 9.**

*ECG shows short PQ interval and QRS complex with negative T wave in cattle with hypomagnesemia.*

flattened/widened T wave and short S-T segment. Hypercalcemia may cause acute myocardial infarction.

Hypomagnesemia tetany or grass tetany is caused by a deficiency of magnesium characterized by ataxia, recumbency, neuromuscular irritability, convulsions and tetanic spasms [25]. Cattle with hypomagnesemia (**Figure 9**) subjected to ECG shows short P-Q interval and QRS complex. The T wave is negative and there is a lesser degree of shortening of the Q-T interval.

### **3. Conclusions**

Electrocardiography is currently the best method available for the detection of cardiac arrhythmias and conduction abnormalities [26]. Since Einthoven's invention of the first electrograph in 1895, there have been major advances in the study of cardiac diseases in both humans and animals. In cattle the base apex lead system is the most suitable for monitoring of cardiac function in cattle [9, 10]. Today, ECG is widely used in the field of veterinary medicine for the detection of cardiac arrhythmias and conduction abnormalities as well as to identify electrolyte and mineral imbalances which is valuable in the diagnosis of various disease conditions.
