Library of Congress Cataloging-in- Publication Data. ECG interpretation made incredibly easy!. —. 5th ed. p. ; cm. Includes bibliographical references and index . Interpreting the ECG. •Rate. •Rhythm. - Ectopic beats? •Axis. •Intervals. - Blocks? •Atrial Abnormalities. •Ventricular hypertrophy. •ST/T changes. P wave = atrial depolarisation. PR Interval = impulse from atria to ventricles to ventricles. QRS complex = ventricular depolarisation. ST segment = isoelectric -.
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Confidential. 12 Lead ECG Interpretation. Deborah Klein, MSN, RN, ACNS-BC, CCRN, CHFN, FAHA. Clinical Nurse Specialist, Coronary ICU, Heart Failure ICU, . To get the most out of the Basic ECG Interpretation Study Day please read this Package prior to If you are not confident in your ECG knowledge and / or it has. A simple, step-by-step guide to reading an ECG (also known as ECG interpretation), with included ECG examples.
An ECG is simply a representation of the electrical activity of the heart muscle as it changes with time, usually printed on paper for easier analysis. Like other muscles, cardiac muscle contracts in response to electrical depolarisation of the muscle cells. It is the sum of this electrical activity, when amplified and recorded for just a few seconds that we know as an ECG.
Basic Electrophysiology of the Heart see Figure 1 The normal cardiac cycle begins with spontaneous depolarisation of the sinus node, an area of specialised tissue situated in the high right atrium RA. A wave of electrical depolarisation then spreads through the RA and across the inter-atrial septum into the left atrium LA.
The atria are separated from the ventricles by an electrically inert fibrous ring, so that in the normal heart the only route of transmission of electrical depolarisation from atria to ventricles is through the atrioventricular AV node.
The AV node delays the electrical signal for a short time, and then the wave of depolarisation spreads down the interventricular septum IVS , via the bundle of His and the right and left bundle branches, into the right RV and left LV ventricles.
Hence with normal conduction the two ventricles contract simultaneously, which is important in maximising cardiac efficiency. After complete depolarisation of the heart, the myocardium must then repolarise, before it can be ready to depolarise again for the next cardiac cycle.
Figure 1. The wave of electrical depolarisation spreads from the atria down though the IVS to the ventricles. So the direction of this depolarisation is usually from the superior to the inferior aspect of the heart.
The direction of the wave of depolarisation is normally towards the left due to the leftward orientation of the heart in the chest and the greater muscle mass of the left ventricle than the right. This overall direction of travel of the electrical depolarisation through the heart is known as the electrical axis.
A fundamental principle of ECG recording is that when the wave of depolarisation travels toward a recording lead this results in a positive or upward deflection. When it travels away from a recording lead this results in a negative or downward deflection. Figure 2. Six of these are recorded from the chest overlying the heart — the chest or precordial leads. Four are recorded from the limbs — the limb leads. It is essential that each of the 10 recording electrodes is placed in its correct position, otherwise the appearance of the ECG will be changed significantly, preventing correct interpretation.
The limb leads record the ECG in the coronal plane, and so can be used to determine the electrical axis which is usually measured only in the coronal plane. A horizontal line through the heart and directed to the left exactly in the direction of lead I is conventionally labelled as the reference point of 0 degrees 0 o.
A detailed explanation of how to determine the axis is beyond the scope of this article but the principles mentioned here should help readers to understand the concepts involved.
Figure 3. Transverse section of the chest showing the orientation of the six chest leads in relation to the heart Voltage and timing intervals It is conventional to record the ECG using standard measures for amplitude of the electrical signal and for the speed at which the paper moves during the recording.
This allows: Easy appreciation of heart rates and cardiac intervals and Meaningful comparison to be made between ECGs recorded on different occasions or by different ECG machines. The amplitude, or voltage, of the recorded electrical signal is expressed on an ECG in the vertical dimension and is measured in millivolts mV.
On standard ECG paper 1mV is represented by a deflection of 10 mm. An increase in the amount of muscle mass, such as with left ventricular hypertrophy LVH , usually results in a larger electrical depolarisation signal, and so a larger amplitude of vertical deflection on the ECG.
Lateral ventricular infarction. Pre- excitation. Left ventricular hypertrophy.
Inferior infarction. Probably misplaced electrodes. If the rhythm is wide QRS complex tachycardia, then the cause is probably ventricular tachycardia. Up to baseline.
ST-segment depression is particularly suspicious in the chest leads. Prinzmetal's angina coronary vasospasm. Early repolarization. Nonspecific intraventricular conduction disturbance. Brugada syndrome. Takotsubo cardiomyopathy. Post cardioversion. Pulmonary embolism. Aortic dissection engaging the coronary arteries. Left ventricular aneurysm.
Physiological ST-segment depression. High sympathethic tone. Heart failure. Should be positive accepted in lead V1 and lead III. In some instances the T-wave in most leads. Rarely, all T-waves normal in chest leads.
One type of post-ischemic T-wave inversion is especially acute, namely Wellen's syndrome characterized by deep T-wave inversions in V1—V6 in patient with recent episodes of chest pain. Cerebrovascular insult bleeding. Perimyocarditis after normalization of the ST-segment elevation, T-waves become inverted in perimyocarditis.
Occasionally perimyocarditis. A complete list of malignant ventricular drugs causing QT prolongation can be found here. May cause malignant ventricular low heart rate.
It is largest in V3— arrhythmia. All changes are of interest and may indicate pathology. Clinical context ECG changes should be put into a clinical context. For example, ST-segment elevations are common in the population and should not raise suspicion of myocardial ischemia if the patient do not have symptoms suggestive of ischemia.
The guide continues on the next page. The axis is calculated to the nearest degree by the ECG machine. These leads must have evident R-waves, or R-waves larger than S-waves.