Читать книгу Predicting Heart Failure - Группа авторов - Страница 53

This ECG is generated by a method called electrocardiography, where several electrodes are placed on the patient’s heart, legs, and arms and monitor the pulses for around 10 minutes. The technique measures the electrical activity of each heartbeat resulting in an electrocardiogram that shows the heart’s functionality. The electrocardiogram generated during the electrocardiography technique is a graph that depicts the characteristic of voltage versus time of the heart’s electrical activity. During each cardiac cycle, these electrodes detect the minor electrical changes that occur as a result of cardiac muscle depolarization and repolarization. Several cardiac anomalies, such as cardiac rhythm disruptions (e.g. atrial fibrillation and ventricular tachycardia), insufficient coronary artery blood flow (e.g. myocardial ischemia and myocardial infarction), and electrolyte disturbances (e.g. hypokalemia and hyperkalemia) cause changes in the usual ECG pattern. An illustration of the ECG test is shown in Figure 2.2. An ECG test is required only if the patient has any risk factors, such as hypertension, or physical discomforts, such as angina or palpitations including irregular heartbeats or rapid heartbeats. Patients with an existing history of heart disease are required to do the ECG test. Moreover, healthy individuals with a family history of heart disease are advised to do the ECG test if they are going to begin any heavy exercise routine or heavy labor routine.

Figure 2.2 ECG. E denotes electrodes placed for detecting the small electrical changes induced by cardiac muscle depolarization. The graph of voltage versus time of the heart’s electrical activity is showing in the ECG monitor. A physician/nurse is assigned to supervise the ECG test.

The major waves of a single ECG pattern and the normal values of ECG signals for normal heart rate are given in Figure 2.3. Arrhythmia is detected by verifying against the intervals shown in the table.

Figure 2.3 Major waves of a single ECG signal and the normal values of ECG signals.