ECG is the primary method for diagnosing cardiac arrhythmias. This publication summarizes the signs of a normal ECG. ECG recording is carried out in a comfortable position for the patient, the breathing should be quiet. For the ECG registration often use 12 main leads: 6 extremity lead and 6 chest leads. The project Ecg4me.com offers microalternatnation analysis of the six leads (applicable only electrodes that are imposed on limbs). They allow you to identify probable deviations of the heart itself. Through the project Ecg4me.com is possible analysis and by 12-lead. But an untrained person may experience difficulty with a regular arrangement of electrodes at home. This can lead to incorrect recording of the electrocardiogram. Therefore, the device CARDIOVISOR, which records 12 leads, cardiologists acquire it mainly.
To get six standard leads the electrodes, their impose in the following way:
• I lead: left arm (+) and right arm (-)
• II lead: left foot (+) and right arm (-)
• III lead: left foot (+) and left arm (-)
• aVR – augmented unipolar right lead
• aVL - augmented unipolar left lead
• aVF - augmented unipolar foot lead
The figure shows the electrocardiogram obtained by the client in the Ecg4me.com project
Each lead characterizes the work of a certain area of ??the myocardium. I and aVL leads reflect the potentials of the anterior and lateral wall of the left ventricle. III and aVF leads reflect the potentials of the posterior wall of left ventricle. II lead is an intermediate and confirms the changes in the anterolateral or posterior wall of the left ventricle.
The heart consists of two atriums and two ventricles. The mass of atrial is much smaller than that of the ventricles. Electrical changes associated with atriums are small therefore. These are related to P-wave. In turn, high-amplitude oscillations recorded on the ECG during ventricular depolarization – it is QRS complex. T-wave associated with the return of the ventricles in the resting state.
When analyzing the ECG follow a strict sequence:
• Heart rhythm
• Waves, which reflect the conduction
• Electrical axis of heart
• Description of the QRS complex
• Description of the ST segment and T-wave
Heart rhythm and heart rate
Heart rhythm is an important heart work indicator. In normal sinus rhythm (the name is associated with sinus node - pacemaker. Its work is related to momentum transfer and the heartbeat). If the depolarization begins not in sinus node, then the talk about arrhythmias and rhythm is named after the parts where to start depolarization. Heart rate (HR) determined by the distance between P-waves on ECG. Heart rhythm is normal, if the duration of R-R- waves is the same or has slight variation (10%). The heart rate is 60-80 beats per minute in normal state. ECG machine holds out a paper at a speed of 25mm s, therefore, a large square (5mm) corresponds to 0.2 seconds (sec) or 200 milliseconds (ms). Heart rate is measured by the formula
HR = 60/R-R,
where R-R is the distance between the highest waves are associated with ventricular contraction.
Acceleration of the rhythm is called tachycardia, and bradycardia is slowing of the rhythm.
ECG analysis should conduct a cardiologist. The client of the project Ecg4me.com can do their own ECG using CARDIOVISOR. All calculations will done computer program. The patient sees an already the end result, which is analyzed by the system.
Waves, which reflect the conduction
Over the waves between P-QRS-T waves we can judge about conductivity of the electrical impulse between parts of the heart. PQ interval makes 120-200 ms (3-5 small squares) in normal state. You can judge about conduct of the pulse from the auricles through the atrioventricular node to the ventricles by the PQ-wave. QRS complex characterizes ventricles activation. The width of the QRS complex is measured from the beginning of Q-wave till the end of S-wave. This width is 60-100 ms in normal state. Also look at the nature of this complex waves. Q-wave should be no more than 0.04 seconds in duration and shall not exceed 3 mm in depth in normal state. Abnormal Q-wave may indicate a myocardial infarction.
QT interval describes the total duration of systole (contraction) of ventricular. QT interval includes interval from the beginning of QRS complex to the end of T-wave. For the calculation of the QT interval is often used Bazett formula. This formula takes into account the dependence of the QT interval on the frequency of the rhythm (QTc). QTc interval makes 390-450 ms in normal state. QT-wave prolongation indicates the development of coronary heart disease, arteriosclerosis, rheumatism, or myocarditis. The shortening of the QT interval may be indicative of hypercalcemia.
All intervals that reflect the conduction of the electric pulse, calculated by a special program that provides a fairly accurate test results, which are visible in the mode of the cabinet diagnostics in system Ecg4me.com.
Electrical axis of heart
Position determination of the electrical axis of heart allows to reveal conduction disturbances of the electric pulse area. Evaluation of the electrical axis of heart makes by cardiologists. When using Ecg4me.com, data on the status of electrical axis of the heart are automatically calculated and the patient can see the results in his cabinet of diagnosis. Look at the height of the wave to determine the electrical axis of heart. R-wave must be greater than S-wave (counting from the isoelectric line) in I, II and III leads in the normal state. Right axis deviation (S-wave more than R-wave in I lead) indicates problems in the right ventricle, and the deviation to the left (S-wave more than R-wave in II and III leads) may indicate left ventricular hypertrophy.
Description of the QRS complex
QRS complex arises from the conduct of the pulse on the septum and ventricular myocardium. This is characteristic of their work. Pathological Q-wave is absent in the normal state (no wider than 20-40 ms, and no deeper than 1 / 3 R-wave). P-wave is negative in aVR lead. QRS complex is oriented downward from the isoelectric line. The width of the QRS complex is less than 120 ms in the normal state. Increasing this interval may be because of His' bundle blockade (conduction disturbances).
Figure. Negative P-wave in aVR lead (isoelectricline shown in red).
P-wave reflects the propagation of the electric pulse in both atriums. The initial part of P-wave characterizes the activity of the right atrium, and the final part - the left atrium. P-wave should be positive in I and II leads, aVR - negative, positive in aVF and it is unstable in the III and aVL leads usually (can be positive, inverted or diphasic) in the normal state. The width of the P-wave is not less than 0.12 seconds (120ms) in the normal state. When the width of the P-wave is increased, or if it doubles, you can talk about disorder of impulse conduction. There is atrioventricular heart block(Figure).
Figure. Doubling and increase width of the P-wave
ST segment and T-wave description
ST segment corresponds to the period when both ventricles are fully covered by the excitation. It is measured from the end of S to the beginning of the T-wave. The duration of ST depends on the pulse. ST segment is located on the isoline in the normal state, ST depression may be up to 0.5 mm, its rise in the standard leads should not exceed 1 mm. ST-segment elevation is observed in acute myocardial infarction and pericarditis, and depression indicates ischemia or the effect of cardiac glycosides.
T-wave characterizes the process of repolarization (ventricular return to the initial state). T-wave is directed upwards in I and II leads, but in aVR lead it will always be negative during normal heart function. Tall and tapered T-wave observed in hyperkalemia, and flat and elongated wave indicates the reverse process - hypokalemia. Negative T-wave in leads I and II may be indicative of ischemia, infarction, hypertrophy of the right and left ventricle, or of pulmonary embolism.
We describe the main parameters that are used for ECG analysis by the standard method. Ecg4me.com project, offers ECG analysis, which is based on the method of dispersion mapping. It is based on creating an information and topological models of small electrocardiogram oscillations - miсroalternations of ECG-signal. Analysis of these deviations allows to reveal pathology in work of heart at earlier stages, in contrast to standard method of ECG analysis.