Snímka 1 Electrocardiography basics This presentation will deal with the basics of ECG description as well as the physiological basics of Snímka 2 Lecture overview 1. Cardiac conduction system functional anatomy 2. ECG basics Lead placement peaks and waves electrical axis conduction system and ECG 3. ECG description methodology approaches to ECG description Example of ECG description In the first section we will be talking about the heart conduction system and how is electric impulse transmitted through cardiac muscle. Understanding this point is important in order to understand the electrocardiography itself. In the second part, we will try to explain what peaks and waves electrocardiogram (ECG) consists of. In addition, conduction system in relation to ECG will be described. Lastly, the ways of ECG description are going to be introduced. Snímka 3 1. Cardiac conduction system The components of cardiac conduction system includes: Sinoatrial node Atrioventricular node His bundle Left bundle branch - Left anterior fascicle - Left posterior fascicle E. Right bundle branch F. Purkinje fibers
Snímka 4 1. Cardiac conduction system Action potential and the subsequent electrical impulse is created in sinoatrial node which is also referred Sinoatrial node Atrioventricular node to as primary heart pacemaker, and further propagated into atrioventricular node. Here the electrical impulse is slowed down in order to let the ventricles fill with blood due to atria contraction, and further transmitted to His bundle and left and right bundle branches, where the later one speeds up the electrical impulse again, so all muscle fibers in ventricles are stimulated/depolarized at the same time. Snímka 5 2. Electrocardiography basics The heart generates its own electrical signal as mentioned before, (also called an electrical impulse), and this can be recorded by placing electrodes on the chest or limbs. This is called an electrocardiography and the result of electrocardiography is electrocardiogram. Snímka 6 2. Lead placement The standard 12-lead electrocardiogram is a representation of the heart's electrical activity recorded from electrodes on the body surface Generally, we recognize the so called bipolar and unipolar leads. To bipolar leads, the standard limb leads I, II, III (full circle) belong. The unipolar leads include the augmented leads avr, avl and avf (dashed circle) and chest leads V1-V6 (dotted circle).
Snímka 7 2. Bipolar lead placement For bipolar leads, we place electrodes as follows: The red color electrode goes to right arm, yellow goes to left arm, green goes to left foot, and black (which is earthed electrode) goes to right foot. The standard lead I looks to electrical activity of heart from the right arm to left arm (or lateral direction), lead II looks to heart from right arm to left foot (or left superior to inferior direction), and lead III reflects the electrical activity from left arm to left foot (or right superior to inferior direction). Note: The colors of electrodes are typical and standard for a particular region, i.e. in Europe. Nevertheless, in other regions (e.g. in USA) these colors may be different, but they remain the same throughout the region. Snímka 8 2. Unipolar lead placement Augmented leads are named as avr, avf and avl, where a stands for augmented V stands for voltage R stands for right arm L stands for left arm F stands for foot Practically, the augmented leads are hidden inside the standard leads, so the correct positioning of standard limb leads (and vice versa) ensures also the correct position of augmented leads. Augmented leads looks to electrical activity of heart from frontal plane.
Snímka 9 2. Unipolar leads placement V1 The unipolar chest leads (or precordial leads) look to electrical V6 activity of heart from the horizontal plane. The proper positioning of chest leads ensures the proper interpretation of ECG. The positioning of electrodes is as follows: V1 (red color electrode) - right 4 th intercostal space V2 (yellow color electrode) - left 4 th intercostal space V3 (green color electrode) - halfway between V2 and V4 V4 (brown color electrode) - left 5 th intercostal space, mid-clavicular line V5 (black color electrode) - horizontal to V4, anterior axillary line V6 (violet color electrode) - horizontal to V5, mid-axillary line Note: The colors of electrodes are typical and standard for a particular region, i.e. in Europe. Nevertheless, in other regions (e.g. in USA) these colors may be different, but they remain the same throughout the region. Snímka 10 2. Electrocardiogram J point Generally, there are 2 waves and 3 peaks on the ECG. The waves represents the P and T wave, peaks are Q, R, and S. Besides we also recognize (important for ECG description) PQ/PR segment, ST segment, QT interval and RR interval. PQ/PR segment from the beginning of P wave to Q peak ST segment from the end of S peak (J point) to the beginning of T wave QT interval from the beginning of QRS to the end of T wave PQ/PR segment from the end of P wave, to the beginning of QRS complex RR interval distance between 2 consecutive R peaks
Note: Sometimes after T wave, another smaller wave can be found. This is a U wave, and its origin is not clear. However, it is hypothesized, that this U wave represents either afterdepolarizations" in the ventricles, or repolarization of interventricular septum. Snímka 11 2. Principle of electric activity detection The reference point is electrode If the depolarization wave is moving towards electrode, the amplitude is positive If the depolarization wave is moving away from electrode, the amplitude is negative What is important for electric activity detection, is the fact, that the electrode is a reference point. Whenever the electric impulse (depolarization wave) travels towards this electrode, the amplitude of the ECG amplitude (peak or wave) is mostly positive (upwards on ECG). Whenever the depolarization wave travels away from this electrode, the ECG amplitude (peak or wave) is mostly negative (downwards on ECG). Note: Since we have a 12-lead ECG, each lead represents a reference point. In other words, we have 12 reference points, each looking on heart from different side. Since the ventricle myocardium has the largest amount of muscle fibers and therefore electrical activity, these rules reflect mainly the ventricle depolarization through QRS complex.
Snímka 12 2. Principle of electric activity detection If the electrode is in the middle of the electrical axis, the amplitude is biphasic (postive and negative) When this electrode is in the middle of electrical activity of heart, the amplitude is biphasic (both negative and positive). The reason for this, is, that the impulse travels to the electrode (positive amplitude) and then it turns away from the reference point (negative amplitude). Note: Since we have a 12-lead ECG, each lead represents a reference point. In other words, we have 12 reference points, each looking on heart from different side. Since the ventricle myocardium has the largest amount of muscle fibers and therefore electrical activity, these rules reflect mainly the ventricle depolarization through QRS complex. Snímka 13 2. Principle of electric activity detection The above mentioned can be best presented on this ECG. Look for the precordial leads V1 to V6. Each lead represents one reference point. V1 is positioned in the 4th intercostal space parasternally right (see previous slides) in the region of sinoatrial node. This means that the electrical impulse or depolarization wave would move away from this electrode. Therefore QRS complex in V1 would be mostly negative. On the other hand, lead V6 is positioned in 5th intercostal space midline axillary line, in the region of lateral-posterior wall of left ventricle, therefore the QRS complex would be mostly positive. Note: The lead V3 has equally positive and negative amplitude in QRS complex. This is because the lead lies exactly in the middle of electrical activity, thus the impulse travels equally towards and equally away from the V3 reference point.
This is referred to also as to transition zone. Snímka 14 2. Electrical axis Is given by the sum of vectors of electrical potentials at the given time The heart's electrical axis refers to the general direction of the heart's depolarization wavefront (or mean electrical vector) in the frontal plane. RA II I LF LA III The electrical axis is a sum of electrical potentials at a given time. Under normal circumstances, the impulse travels from sinoatrial node (right up side) to the left ventricle (left bottom side). This is the normal electrical axis of the heart, reflected by the QRS complex in standard and augmented unipolar leads, reflected by the most positive QRS complex which would be in lead II. Snímka 15 2. Electrical axis Approach to electrical axis determination +ve stands for positive QRS complex - ve stands for negative QRS complex A panel lead I & avf are +ve = normotype lead I & avf are -ve = os v NW zone lead I -ve & avf are +ve = rightward axis lead I +ve & avf is -ve - than the lead II is important B panel lead II +ve = normotype lead II -ve = leftward axis Firstly, start with A panel, when the last criteria (lead I +ve and avf ve) is met, then continue to panel B.
Snímka 16 Applying the above mentioned rule, this is the normal electrical axis. The lead I and lead avf, both are +ve Snímka 17 2. Conduction system and ECG The conjunction of impulse conductance through heart muscle to P R Q S T ECG output is as follows: Sinoatrial node depolarizes and send electrical impulse to atrioventricular node. Atria depolarize. This is on ECG represented by the P wave. In the atrioventricular node, the impulse is slowed down, in order to let the ventricles fill with blood from atria contraction. This on ECG is represented by PQ segment (from the end of P wave to beginning of QRS complex). The electrical impulse is then quickly propagated through the His bundle to both bundle branches and ventricle myocardium. Fast ventricle depolarization is reflected by the QRS complex, where Q represents depolarization of interventricular septum. RS then depolarization of the ventricles themselves. After ventricle depolarization, ventricle repolarization occurs. This is represented by ST segment on ECG.
Snímka 18 2. Conduction system and ECG R P T Q S Snímka 19 3. Electrocardiogram description methodology 1. Rhythm sinus, non-sinus atrial fibrillation?, AV junction?, malign rhythm? 2. Action regular, irregular 3. Heart rate 4. Electrical axis rightward, leftward, normal 5. Conduction times PQ, QRS, QT 6. Deformities of P, QRS mitral P, biphasic P, QRS deformities rsr config., delta wave 7. Transition zone in precordial leads 8. ST segment isoelectric, depression and elevation 9. T wave positive, negative, flattened, peak 10. Other This represents a step by step guide how to correctly describe ECG without possibility to omit some important stuff. This detailed ECG description is a need-to-know basis for all medical students. 1. First point includes the rhythm, the basic rhythm is a sinus rhythm. The definition of sinus rhythm is when we see a P wave in front of each QRS complex in any, but at least one lead. If You cannot see a sinus rhythm, then think describe the rhythm as nonsinus. (The special attention goes to so-called malign rhythms, which include asystole, pulseless electric activity, ventricular tachycardia and ventricular fibrillation. This is because a patient with such rhythm requires immediate cardiopulmonary resuscitation). 2. Secondly, action is described. This can be either regular or irregular. You can find out regularity by counting RR distance between 2 consecutive QRS complexes, in at least 3 different places within one lead. If the distance is all the same, the action is regular 3. Heart rate, can be calculated by formula 300 divided by [number of big (5mm) squares between two consecutive R peaks] 4. Electrical axis is determined by the formerly mentioned rules. 5. Conduction times in PQ, QRS, and QT segments/intervals. One mm on
ECG paper represents 0.04s, if the paper is moving with speed 25mm/s. The PQ interval should for example measure between 0.12-0.20 s, what means 3-5 mm on ECG paper. 6. Deformities of P wave and QRS complex in each lead we determine, whether the P and QRS are not deformed. The P wave for example may be mitral, biphasic or peaked, on the other hand, the QRS may be deformed by delta wave, or may have a RSR configuration (please refer the next chapter). 7. Transition zone in precordial leads we trie to find where is the middle of the electrical axis, i.e. where is the QRS complex equally positive AND negative. 8. ST segment evaluation we try to find in each lead separately, whether the ST segment isoelectric, depressed or elevated. 9. T wave configuration T wave may be positive, negative, flattened or peaked. Again, we observe T wave in each lead separately. Snímka 20 3. Electrocardiogram description methodology 1. Heart rate (slow-normal-fast) 2. Rhythm (regular-irregular) 3. QRS width (narrow-broad) 4. ST segment (elevation, depression) The above mentioned method is an ultimate method for ECG description. It represents complete view, however, requires much skill, experience, and still is also time consuming. Nowadays, in hastened world, much faster but safe methods of ECG evaluation were developed. For clinical practice, especially when You are not going to be an internist or cardiologist, this method should be sufficient to exclude most life threatening situations. You look to heart rate and You try to answer the most relevant question...is it slow, normal, or fast? You look for rhythm is it regular or irregular? If irregular, then arrhythmias may be the answer
QRS width if the QRS complex is widened, then this could mean a bundle branch blockade ST segment is it elevated or depressed? ST segment points towards cardiac ischemia (ST depression) or myocardial infarction (ST elevation). Answering these 4 questions should rule out or confirm the most dangerous ECG diagnosis. Still, if it is not Your specialty and You are in doubt, call a specialist. Snímka 21 ECG description for surgeons ECG description methodology for surgeons... NB: more of a joke, so please do not take this slide seriously Snímka 22 3. Some physiological values PQ interval 0.12 0.20 sec. QRS complex < 0.12 sec QT interval - < 0.36 sec QT c = (QT/RR 2 ) = <0.44 sec Heart rate 60-90 beats per minute Transition zone V3, V3/V4, V4 Just some basic physiologic values, You should be aware of, when want to describe the ECG.
Snímka 23 4 300/ 4 = 75 bpm Example ECG the description step by step Please find attached ECG protocol In this case: Sinus rhythm (P wave is in front of each QRS complex), best seen in lead II Regular action (distance between RR in lead II is 20 mm Heart rate is 75/min (there are 4 five mm squares between two R peaks, what means 300/4 = 75) Normal electrical axis PQ interval is 0,2sec (5 small squares), QRS interval is 0,1sec (2,5 small square) and QT interval is 0,36sec (9 small squares) P negative in avr (however avr is a mirror reflection of lead II, therefore, no abnormalities are observed). No QRS abnormalities in all leads Transition zone is in V3 (QRS equally positive and negative) ST segment is in isoelectric line, seems to be elevated by 2mm in V2 T wave flattened in avl, otherwise positive Little high-frequency noise in lead III. The final ECG description should read: sinus rhythm, regular action, HR 75/min, normal axis, PQ0,2s, QRS 0,1s, QT 0,36s, P and QRS without deformities, transition zone V3, ST segment elevation in V2 by 2mm otherwise isoelectric, T wave flattened in avl otherwise positive, noise in lead III. Conclusion: normal ECG.
Snímka 24 Interesting ECG - STEMI Snímka 25 Interesting ECG - STEMI Snímka 26 Interesting ECG Ventricular tachycardia This is a 12-lead ECG with monomorphic ventricular tachycardia. Although it might be difficult to describe this ECG according to 10- points description, it is easy to describe with the 4-point description. Heart rate Fast/Slow? fast (approx. 130/min) Rhythm regular/irregular? regular QRS width narrow or broad? broad ST elevation, yes/no? cannot determine Result: broad QRS complex tachycardia, i.e. ventricular tachycardia. Since QRS complexes look the same, it is monomorphic tachycardia. HR is around 130/min, the patient will be most probably
Snímka 27 Interesting ECG Ventricular fibrilation stable, i.e. suitable for pharmacology conversion.