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Waves and INTERVAL
A typical ECG trace of a normal heartbeat (or cardiac cycle) consists of a P wave, a QRS complex and a T wave A small U wave is normally visible in 50-75% of ECGs. The baseline voltage of the electrocardiogram is known as the isoelectric line. Typically the isoelectric line is measured as a portion of the tracing following the T wave and preceding the next P wave.
Analysis and rhythm
Analysis and rhythm
There are some basic rules that can be followed to identify a patient's heart rhythm. What is the rate? Regular or irregular? Are there P waves? Are there QRS complexes? Is there a 1:1 ratio between P waves and QRS complexes? Konstankah PR interval?
P wave
During normal atrial depolarization, the main electrical vector is directed from the SA node to AV node, and spreads from the right atrium into the left atrium. This turns into the P wave on ECG, which is upright in leads II, III, and aVF (since the general electrical activity is toward the positive electrode in those leads), and inverted in aVR (since it is going away from the positive electrode to that lead). A P waves should be upright in leads II and aVF and inverted in aVR to signify cardiac rhythm as Sinus Rhythm.• The relationship between P waves and QRS complexes helps distinguish various cardiac arrhythmias.• The shape and duration of P waves may indicate atrial enlargement.
PR interval
PR interval is measured from the beginning of the P wave to the beginning of the QRS complex, which is usually the length of 120-200 ms. On an ECG tracing, is associated with 3-5 small boxes.• PR interval of more than 200 ms may indicate a first degree heart block.• short PR interval may indicate pre-excitation syndrome via an additional pathway leading to early ventricular activation, as seen in Wolff Parkinson White syndrome.• A variable PR interval may indicate other types of heart block.• PR segment depression may indicate atrial injury or pericarditis.• The morphology of P waves on a single lead ECG can indicate an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia.
QRS complexes
Structure of the ECG QRS complex is associated with ventricular depolarization. Because the ventricles contain more muscle mass than the atria, the QRS complex is greater than P waves In addition, because the system of His / Purkinje coordinate ventricular depolarization, the QRS complex tends to look "straight" rather than rounded due to the speed of conduction. Normal QRS complex duration 0,06-0.10 s (60-100 ms) is indicated by three small squares or less, but any abnormality of conduction takes longer, and causes the expansion of the QRS complex.Not every QRS complex contains a Q wave, R wave and S wave By convention, any combination of these waves can be referred to as the QRS complex. However, interpretation of the ECG is difficult to actually naming a definite need in a number of waves. Some authors use lowercase and large, depends on the relative size of each wave. For example, an Rs complex would show a positive deflection, while a rS complex would show a negative deflection. If both complexes were labeled RS, it would be impossible to appreciate this distinction without viewing the actual ECG.• The duration, amplitude, and morphology of the QRS complex is useful for diagnosing cardiac arrhythmias, conduction abnormalities, ventricular hypertrophy, cardiac infarction bibs, electrolyte disturbances, and other sickness.• Q waves can be normal (physiological) or pathological. If there is, normal Q waves represent depolarization of the interventricular septum. For this reason, it can be referred to as septal Q waves and can be assessed in the lateral leads I, aVL, V5 and V6.• Q waves greater than 1 / 3 R wave height, length greater than 0.04 s (40 ms), or in the right precordial leads is considered abnormal, and may represent myocardial infarction.
ST segment
P wave
During normal atrial depolarization, the main electrical vector is directed from the SA node to AV node, and spreads from the right atrium into the left atrium. This turns into the P wave on ECG, which is upright in leads II, III, and aVF (since the general electrical activity is toward the positive electrode in those leads), and inverted in aVR (since it is going away from the positive electrode to that lead). A P waves should be upright in leads II and aVF and inverted in aVR to signify cardiac rhythm as Sinus Rhythm.• The relationship between P waves and QRS complexes helps distinguish various cardiac arrhythmias.• The shape and duration of P waves may indicate atrial enlargement.
PR interval
PR interval is measured from the beginning of the P wave to the beginning of the QRS complex, which is usually the length of 120-200 ms. On an ECG tracing, is associated with 3-5 small boxes.• PR interval of more than 200 ms may indicate a first degree heart block.• short PR interval may indicate pre-excitation syndrome via an additional pathway leading to early ventricular activation, as seen in Wolff Parkinson White syndrome.• A variable PR interval may indicate other types of heart block.• PR segment depression may indicate atrial injury or pericarditis.• The morphology of P waves on a single lead ECG can indicate an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia.
QRS complexes
Structure of the ECG QRS complex is associated with ventricular depolarization. Because the ventricles contain more muscle mass than the atria, the QRS complex is greater than P waves In addition, because the system of His / Purkinje coordinate ventricular depolarization, the QRS complex tends to look "straight" rather than rounded due to the speed of conduction. Normal QRS complex duration 0,06-0.10 s (60-100 ms) is indicated by three small squares or less, but any abnormality of conduction takes longer, and causes the expansion of the QRS complex.Not every QRS complex contains a Q wave, R wave and S wave By convention, any combination of these waves can be referred to as the QRS complex. However, interpretation of the ECG is difficult to actually naming a definite need in a number of waves. Some authors use lowercase and large, depends on the relative size of each wave. For example, an Rs complex would show a positive deflection, while a rS complex would show a negative deflection. If both complexes were labeled RS, it would be impossible to appreciate this distinction without viewing the actual ECG.• The duration, amplitude, and morphology of the QRS complex is useful for diagnosing cardiac arrhythmias, conduction abnormalities, ventricular hypertrophy, cardiac infarction bibs, electrolyte disturbances, and other sickness.• Q waves can be normal (physiological) or pathological. If there is, normal Q waves represent depolarization of the interventricular septum. For this reason, it can be referred to as septal Q waves and can be assessed in the lateral leads I, aVL, V5 and V6.• Q waves greater than 1 / 3 R wave height, length greater than 0.04 s (40 ms), or in the right precordial leads is considered abnormal, and may represent myocardial infarction.
ST segment
The ST segment connects the QRS complex and T wave and a duration of .08 to .12 s (80-120 ms). This segment begins at the J point (junction between the QRS complex and ST segment) and ends at the beginning of the T wave However, since it is usually difficult to determine exactly where the ST segment ends and the T wave begins, the relationship between ST segment and T wave should be examined together. Typical ST segment duration is usually around 0.08 sec (80 ms), which is basically equivalent to the level of PR and TP segment.• The normal ST segment slightly concave upward.• ST segments flat, slightly sloping, or declining may indicate coronary ischemia.• ST segment elevation may indicate myocardial infarction. An elevation of 1 mm and longer than 80 ms after the J-point Rate this size could be a false positive rate of 15-20% (which is slightly higher in women than men) and false negatives by 20-30%.
T wave
The T wave represents the repolarization (or recovery) of the ventricles. The interval from the beginning of the QRS complex to the peak of the T wave is called the absolute refractory period. The last half of the T wave is referred to as the relative refractory period (or vulnerable period).In most leads, positive T wave. However, the normal negative T waves in aVR. Lead V1 may have a positive T wave, negative, or biphasic. In addition, it is not uncommon to have an isolated negative T wave in lead III, aVL, or aVF.• inverted T waves (or negative) can be a coronary ischemia, Wellens' syndrome, left ventricular hypertrophy, and CNS disorders.• High T waves or "tented" may indicate hyperkalemia. Flat T waves may indicate coronary ischemia or hypokalemia.• earliest electrocardiographic finding of acute myocardial infarction is sometimes the hyperacute T wave, which can be distinguished from hyperkalemia by the broad base and slight asymmetry.• When a conduction abnormality (eg, bundle branch block, paced rhythm), the T wave should be deflected opposite the terminal deflection of the QRS complex, known as appropriate T wave discordance.QT interval
QT interval was measured from the beginning of the QRS complex to the end of T wave Normal QT interval is usually about 0.40 s. QT interval corrected in addition to the essential in the diagnosis of long QT syndrome and short QT syndrome. QT interval varies based on heart rate, and various correction factors have been developed to correct the QT interval for heart rate.The most commonly used to correct the QT interval for rate ever formulated by Bazett and published in 1920. Bazett formula isWhere QTc is the QT interval corrected for rate, and RR is the interval from the beginning of one QRS complex to the beginning of the next QRS complex, measured in seconds. However, this formula tends to be inaccurate, and over-corrects at high heart rates and under-corrects at low heart rates.U wave
U wave is not always visible. It is typically small, and by definition, follows the T wave U waves are thought to represent repolarization of the papillary muscles or Purkinje fibers. Prominent U waves are often seen in hypokalemia, but may exist in hypercalcemia, thyrotoxicosis, or exposure to digitalis, epinephrine, and Class 1A and 3 antiarrhythmics, as well as in congenital long QT syndrome and intracranial hemorrhage in the circumstances. An inverted U wave that may reflect myocardial ischemia or volume overload in the left ventricle.
