As explained in Figure 1, leads II and AVR are best suited for recording the P wave. Characteristics of a normal p wave: [ 1 ] The maximal height of the P wave is 2.5 mm in leads II and / or III. R-wave peak time (Figure 9) is the interval from the beginning of the QRS-complex to the apex of the R-wave. ST segment deviation occurs in a wide range of conditions, particularly acute myocardial ischemia. Right ventricular hypertrophy. An isolated and often large Q-wave is occasionally seen in lead III. The ST segment must always be studied carefully since it is altered in a wide range of conditions. This is rather easy to understand because lead II is angled alongside the P-wave vector, and the exploring electrode is located in front of the P-wave vector (Figure 2, right-hand side). The P-wave is frequently biphasic in V1 (occasionally in V2). Some leads may display all waves, whereas others might only display one of the waves. Three criteria were used to distinguish right from left PV: 1) a positive P-wave in lead aVL and the amplitude of P-wave in lead I ≥50 μV indicated right PV origin (specificity 100% and 97%, respectively); 2) a notched P-wave in lead II was a predictor of left PV origin (specificity 95%); and 3) the amplitude ratio of lead III/II and the duration of positivity in lead V1were also helpful in distinguishing left versus right PV origin. The second positive wave is called “R-prime wave” (R’). P-waves travel sooner than other seismic waves and therefore are the first signal from an earthquake to reach at any affected place or at a seismograph. aVF: positive T-wave, but occasionally flat. If the R-wave is missing in lead V2 as well, then criteria for pathology is fulfilled (two QS-complexes). However, it is not rare to have an additional – accessory – pathway between the atria and the ventricles. This is shown in Figure 3 (upper panel). If QRS duration is ≥ 0,12 seconds (120 milliseconds) then the QRS complex is abnormally wide (broad). The P-wave is frequently biphasic in V1 (occasionally in V2). Write. Published by Elsevier Inc. All rights reserved. The time dependence of the displacement at any single point in space is often an oscillation about some equilibrium position. The vector is directed backward and upwards. Heart failure may cause ST segment depression in the left lateral leads (V5, V6, aVL and I) and these depressions are generally horizontal or downsloping. These waves travel in a transversal direction. Septal q-waves are small q-waves frequently seen in the lateral leads (V5, V6, aVL, I). Sinus Bradycardia. P waves are the fastest seismic waves and can move through solid, liquid, or gas. The negative deflection is normally <1 mm. These waves can travel through solid, liquid, and gas. PLAY. The next discussion will be devoted to characterizing important and common ST-T changes. Thus, in this chapter, you will learn the physiological basis of all ECG waves and how to determine whether the ECG is normal or abnormal. Note that the upper reference limit (0.22 seconds) should be related to the age of the patient; 0.20 seconds is more suitable for young adults because they have faster impulse conduction. T-wave inversions are frequently misunderstood, particularly in the setting of ischemia. In each of these conditions, the depolarization is abnormal and this affects the repolarization so that it cannot be carried out normally. They may be gigantic (10 mm or more) or less than 1 mm. The term block is somewhat misleading since it is actually a matter of abnormal delay and not a block per se. U-wave inversion is rare but when seen, it is a strong indicator of pathology, particularly for ischemic heart disease and hypertension. Trough = Lowest point of the wave. However, there is one notable exception, when an upsloping ST segment is actually caused by ischemia and the condition is actually alarming. The ST segment corresponds to the plateau phase of the action potential (Figure 13). Panel B in Figure 6 shows a net negative QRS complex because the negative areas are greater than the positive area. Some expert consensus documents also note that any ST segment depression in V2–V3 should be considered abnormal (because healthy individuals rarely display depressions in those leads). This is considered a normal finding provided that an R-wave is seen in V2. Characteristics of normal P waves include A. one P preceding each QRS complex. The U-wave is seen occasionally. The S waves are the second wave to reach a seismic station measuring a disturbance. Impulse originates in the SA Node-One P per QRS -All waves, intervals, and rate WNL. The ST segment may be displaced upwards (ST segment elevation) or downwards (ST segment depression). Please refer to Figure 37. P waves travel at speeds between 1 and 14 km per second, while S waves travel significantly slower, between 1 and 8 km per second. These arrive after P waves. Figure 15 B. By applying a P‐wave recognition program to eliminate extra systole, a signal of >250 beats was averaged from a standard 12‐lead ECG and the noise amplitude was reduced to <0.5 μV. The negative deflection is normally <1 mm. However, apart from the delta wave, the R-wave will appear normal because ventricular depolarization will be executed normally as soon as the atrioventricular node delivers the impulse to the His-Purkinje system. Spell. Recall that the P-wave in V1 is often biphasic, which is also shown in Figure 3. The first positive wave is simply an “R-wave” (R). The amplitude of any deflection/wave is measured by using the PR segment as the baseline. A normal PR interval ranges between 0.12 seconds to 0.22 seconds. Depolarization of the ventricles generates three large vectors, which explains why the QRS complex is composed of three waves. Assessment of the T-wave represents a difficult but fundamental part of ECG interpretation. The U-wave is most frequently seen in leads V2–V4. The direction of the depolarization (and thus the electrical axis) is generally alongside the hearts longitudinal axis (to the left and downwards). The explanation for this is as follows: As evident from Figure 7, the vector of the ventricular free wall is directed to the left (and downwards). There are two types of ST segment deviations. It should be noted that the term “biphasic” is unfortunate because (1) biphasic T-waves carry no particular significance and (2) a T-wave is classified as positive or inverted based on its terminal portion; if the terminal portion is positive then the T-wave is positive and vice versa. T-wave changes are frequently misunderstood in clinical practice, which the discussion below will attempt to cure. A short QRS complex is desirable as it proves that the ventricles are depolarized rapidly, which in turn implies that the conduction system functions properly. Normal PR interval: 0,12–0,22 seconds. Its amplitude is generally one-fourth of the T-wave’s amplitude. They can still propagate through the solid inner core: when a P wave strikes the boundary of molten and solid cores at an oblique angle, S waves will form and propagate in the solid medium. Study this figure carefully. ECG changes in myocardial ischemia are discussed in section 3 (Acute & Chronic Myocardial Ischemia & Infarction) and a specific chapter discusses ST depression. QRS duration is the time interval from the onset to the end of the QRS complex. This is explained by the fact that T-wave inversions do occur after an ischemic episode, and these T-wave inversions are referred to as post-ischemic T-waves. It is very rare but may cause malignant arrhythmias. Light does not actually pass through the location on the other side of the mirror; it only appears to an observer as though the light is coming from this location. This is seen in bundle branch blocks (left and right bundle branch block), pre-excitation, ventricular hypertrophy, premature ventricular complexes, pacemaker stimulated beats etc. A complete QRS complex consists of a Q-, R- and S-wave. It should be noted, however, that up to 20% of Q-wave infarctions may develop without symptoms (The Framingham Heart Study). This may be explained by right bundle branch block, right ventricular hypertrophy, hypertrophic cardiomyopathy, posterolateral ischemia/infarction (if the patient experiences chest pain), pre-excitation, dextrocardia or misplacement of chest electrodes. This is often (but not always) seen on ordinary ECG tracings and it is explained by the fact that the atria are depolarized sequentially, with the right atrium being depolarized before the left atrium. It is called Wave Propagation Direction. Hyperventilation brings about the same ST segment depressions as physical exercise. aVR displays a negative T-wave. Spontaneous action potentials discharged within the ventricles may depolarize the ventricles. Includes a complete e-book, video lectures, clinical management, guidelines and much more. Volgman AS(1), Winkel EM, Pinski SL, Furmanov S, Costanzo MR, Trohman RG. Short QTc syndrome (QTc <0,390 seconds) is uncommon and can be seen in hypocalcemia and during digoxin treatment. Small Q-waves (which do not fulfill criteria for pathology) may be seen in all limb leads as well as V4–V6. The J point is the point where the ST segment starts. Flashcards. All positive waves are referred to as R-waves. The following must be noted regarding the ST segment: It must also be noted that the J point is occasionally suboptimal for measuring ST segment deviation. It is initially directed forward but then turns left to activate the left atrium (Figure 2, left-hand side). Numerous conditions can diminish the capacity of the atrioventricular node to conduct the atrial impulse to the ventricles. Same as normal sinus rhythm except:-Rate: 40-60. Enlargement of the right atrium is commonly a consequence of increased resistance to empty blood into the right ventricle. The magnitude of depression/elevation is measured as the height difference (in millimeters) between the J point and the PR segment. It reflects the time interval from the start of atrial depolarization to start of ventricular depolarization. R-wave peak time is prolonged in hypertrophy and conduction disturbances. Normal R-wave progression implies that the R-wave gradually increases in amplitude from V1 to V5 and then diminishes in amplitude from V5 to V6 (Figure 10, left-hand side). QT duration and corrected QT (QTc) duration, left anterior descending coronary artery (LAD), Acute & Chronic Myocardial Ischemia & Infarction. Terms in this set (28) Normal Sinus Rhythm. Dominant R-wave in V1/V2 implies that the R-wave is larger than the S-wave, and this may be pathological. ECG interpretation: Characteristics of the normal ECG (P-wave, QRS complex, ST segment, T-wave) – ECG & ECHO. Electrocardiographic P-wave characteristics in patients with end-stage renal disease: P-index and interatrial block This is seen in ischemia, electrolyte disorders (calcium, potassium), tachycardia, increased sympathetic tone, drug side effects etc. A negative T-wave is also called an inverted T-wave. Low amplitudes may also be caused by hypothyreosis. QT duration is inversely related to heart rate; QT duration increases at low heart rate and vice versa. Therefore, the slender individual may present with much larger QRS amplitudes. They leave behind a trail of compressions and rarefactions on the medium they move through. Many of these conditions cause rather characteristic ST segment changes. The electrical currents generated by the ventricular myocardium are proportional to the ventricular muscle mass. The PR interval is the distance between the onset of the P-wave to the onset of the QRS complex. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. Morphological characteristics of P waves during selective pulmonary vein pacing. An algorithm predicting the paced PV was developed and prospectively evaluated in a different population of 20 patients. T-wave progression follows the same rules as R-wave progression (see earlier discussion). Note that the T-wave inversion may actually persist for a period after normalization of the depolarization (if it occurs). Clinicians often perceive this as a difficult task despite the fact that the list of differential diagnoses is rather short. At the heart of ECG interpretation lies the ability to determine whether the ECG waves and intervals are normal. The term ST-T segment changes (or simply ST-T changes) is used to refer to such ECG changes. A common cause of abnormally large T-waves is hyperkalemia, which results in high, pointed and asymmetric T-waves. S ingh (2006) Effects of soil layering on the characteristics of basin-edge induced surface waves and differential ground motion, Jr. of Earthquake Engineering 10, 595-616. First, realize that this “radially-directed” plane wave is in fact a plane wave, and not a cylindrical wave. T-waves that are higher than 10 mm and 8 mm, in men and women, respectively, should be considered abnormal. Left bundle branch block. It is crucial to differentiate normal from pathological Q-waves, particularly because pathological Q-waves are rather firm evidence of previous myocardial infarction. Characteristics of P wave: P waves are the primary waves similar to sound waves in which particles move to and fro in the direction in which the wave is travelling.They have short wavelength and high frequency and are the first wave to arrive a seismograph and can move through solid , liquid and gas. Leads V1-V2 (right ventricle) <0,035 seconds, Leads V5-V6 (left ventricle) <0,045 seconds. The longer the Q-wave duration, the more likely that infarction is the cause of the Q-waves. Figure 16 displays characteristics of ischemic and non-ischemic ST segment elevations. A rather extensive discussion is provided in order to give the reader firm knowledge of normal findings, normal variants (i.e less common variants of what is considered normal) and pathological variants. These ST segment depressions display an upsloping ST segment, typically depressed <1 mm in the J-60 point and the depressions are normalized rapidly after the exercise has ended. As evident from the figure, the normal heart axis is between –30° and 90°. Test. It is negative in lead aVR. The QRS complex is net positive if the sum of the positive areas (above baseline) exceeds that of the negative areas (below baseline). Notice the following wave characteristics and particle motion of the P wave: The deformation (a temporary elastic disturbance) propagates. The atrioventricular (AV) node is normally the only connection between the atria and the ventricles. Pacing from the different PVs produced a P-wave with distinctive characteristics that could be used as criteria in an algorithm to identify the PV of origin with an accuracy of 79%. Prolonged QT duration predisposes to life-threatening ventricular arrhythmias and therefore QT duration must always be assessed. The T-wave amplitude is highest in V2–V3. Ischemic ST depressions display a horizontal or downsloping ST segment (this is a requirement according to North American and European guidelines). This is illustrated in Figure 11. QTc duration is calculated automatically in all modern ECG machines. If an atria becomes enlarged (typically as a compensatory mechanism) its contribution to the P-wave will be enhanced. aurieulaire normale et rétrograde. In leads I, II, aVf, and V2 through V6, the deflection of the P wave is characteristically Most waves move through a supporting medium, with the disturbance being a physical displacement of the medium. Thus, it is the same electrical vector that results in an r-wave in V1 and q-wave in V5. It is not known what engenders the U-wave. Occasionally, the negative deflection is also seen in lead V2. 2. As noted above, the transition from the ST segment to the T-wave should be smooth. The T-wave reflects the rapid repolarization of contractile cells (phase 3) and T-wave changes occur in a wide range of conditions. This explains why these individuals display T-wave inversions in the chest leads. The flat line between the end of the P-wave and the onset of the QRS complex is called the PR segment and it reflects the slow impulse conduction through the atrioventricular node. Left posterior fascicular block is diagnosed when the axis is between 90° and 180° with rS complex in I and aVL as well as qR complex in III and aVF (with QRS duration <0.12 seconds), provided that other causes of right axis deviation have been excluded. If the ectopic focus is located close to the sinoatrial node, the P-wave will have a morphology similar to the P-wave in sinus rhythm. 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