2.1 Electrocardiograph, Electrocardiography and Electrocardiogram

Electrocardiograph is a device/machine used to diagnose heart diseases by measuring electrical potentials on the surface of the body. Electrocardiography is the process of producing an electrocardiogram using an electrocardiographic machine. ECG stands for electrocardiogram, or electrocardiograph. In some countries, “EKG” is abbreviated for electrocardiogram. An electrocardiogram is a graphic record of the voltage produced by cardiac muscle cells during atrial and ventricular depolarization and repolarization plotted against time. In other words it is a graphic representation of electrical activities going on in the heart during depolarization and repolarization. It can provide useful information even about congenital heart diseases. A normal electrocardiogram does not rule out cardiac malformation or other cardiac changes. An abnormal ECG may suggest side of the heart affected or about some other abnormalities related to rate and rhythm of the heart.

2.2 Landmarks in the Development of Electrocardiography

2.3 Application of Electrocardiography in Canine Medicine

2.4 Utility of Electrocardiography

2.5 Limitations of Electrocardiogram

Despite a very useful technique, it has its limitation as with any other technique. It cannot provide definite diagnosis of congestive heart failure. Prognosis during anesthesia or surgical procedures is unpredictable. Heart chamber wall thickness cannot be measured. Diseases of heart valves, endocardium, or pericardium cannot be diagnosed. Obstructive blood flow diseases also remain undiagnosed. Wide variations among breeds and dogs of different body conformations make the interpretation of ECG difficult. Normal electrocardiogram may not always rule out cardiac disease.

2.6 The Electrocardiograph and Recording

2.6.1 Machine

The electrocardiograph is a sensitive voltage metering instrument capable of recording differences of electrical potential up to 1000th of a volt, i.e., 1 mV. The machine consists of a voltage meter and amplifier that is combined with a strip recording device (Fig. 2.1a, b) to give a permanent record. Electrocardiographic tracings are created by the movement of a heated stylus on heat-sensitive recording graph paper. The control panel of electrocardiograph depicts speed, sensitivity, lead selector, off/on switch, and filter (Fig. 2.1c). Electrocardiographic machine is able to run electrocardiograms at the paper speed of 25 or 50 mm/s. The sensitivity switch controls amplification. Normally this switch is positioned at 1, i.e., 1 mV input will cause the stylus to move 1 cm on the paper. Position 2 means 2 cm = 1 mV and 0.5 position means 0.5 cm = 1 mV. Filter is used to reduce disturbances. Stylus position is kept in the center by the position control switch in manual machines. Lead selector switch is used to select the leads or in automatic six channels machine there is no need to select the leads manually. Electrocardiographic machine by different companies may have different setup but basics are the same. It is always advisable to follow the instructions given in the operating manual of the machine for operation.

2.6.2 Electrodes

There are four wire electrodes in standard electrocardiographic cable (shown in bundle marked as 1—Fig. 2.2) and are labeled as right arm (RA), red colored; left arm (LA), yellow colored; right foot or leg (RL), black colored; and left leg or foot (LL), green colored. The other cable (marked as 2—Fig. 2.2) has V leads or exploring chest leads (consisting of six separate electrodes marked as V1, V2, V3, V4, V5, and V6). Alligator clips (Fig. 2.2), flat contact clips, or needles (Fig. 2.3) are used to attach to these electrodes so that these can be attached to the skin of the dog.