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Normal axis. Normal variant e. Restrictive cardiomyopathy Rheumatic heart disease [14] Constrictive pericarditis. Combination of P mitrale and P pulmonale. The appearance of pathological Q waves greater than 0. Further evaluation of the ECG for changes associated with ischemia and infarction involves examination of the ST segment and T waves. Myocardial ischemia implies a decreased blood supply to an area or areas of the heart, and is reversible once blood flow is restored.
Acute myocardial injury is indicated by ST segment elevation, and like ischemia, is reversible with rapid treatment. Remember that injury is reversible with treatment, but infarction is not. A J point elevation in leads V2 through V4 indicates acute injury in the anterior wall. Often, reciprocal changes ST depression appear in other leads.
These patients are considered to have left dominant coronary circulation. Elevated J points and ST segment elevation in the precordial leads V2 through V6, as well as in leads I and aVL, indicate acute anterolateral wall injury.
Deep Q waves suggest that the possibility of scarring has already occurred in the anterior wall. Anterior wall infarct involves the left anterior descending coronary artery; lateral wall injury is often caused by disease in the left circumflex artery.
In the acute stages of MI, ST segments generally elevate within minutes or hours and may stay elevated for several days. During evolution of the MI, the ST segments slowly migrate toward the baseline and the T waves become inverted.
Over the next few weeks, the T waves usually return to normal. Q waves may or may not evolve. Less frequently seen causes include electrolyte abnormalities and central nervous system abnormalities.
ST-T wave abnormalities associated with LVH most commonly occur in the anterolateral leads, and are typically seen as a horizontal or downsloping ST segment and inverted T wave. This pattern is often referred to as "strain" and thought to be related to conduction delays through the thickened diameter of the muscle wall.
Pericarditis, an inflammation of the pericardium, typically produces diffuse ST segment elevation in most leads. Again, as with any ECG evaluation, it is critical to evaluate the clinical context in which the ECG abnormalities occur. Pericarditis typically produces a friction rub that is heard on auscultation; the pain is generally sharp and stabbing in nature, and is often relieved by anti-inflammatory medications see Acute Pericarditis.
Early repolarization is a normal variant and is not indicative of coronary disease. It often occurs in young, healthy individuals, but in the setting of chest pain, it may be confused with myocardial injury. Most of the ST changes that occur in early repolarization involve the precordial leads with J point elevation and a pattern of concave upward ST segments. Electrical impulses reach the ventricles by way of AV junction.
Depolarization then occurs in a wave-like fashion in the ventricles by way of the right and left bundle branches. The left bundle branch bifurcates into the anterior and posterior branches, whereas the right bundle branch is undivided. Any condition that affects the normal electrical conduction in the ventricles will cause a delay, resulting in a widening of the QRS complex.
The next step is to determine in which branch or branches the conduction is delayed or blocked. Once widened, QRS complexes are identified. After an electrical impulse leaves the AV node, it normally travels downward and activates the intraventricular septum in a left to right direction. Since V1 is to the right of the septum and the impulse is coming toward it, a small R wave normally appears in V1.
In RBBB, the impulse travels normally down the left bundle branch, activating the septum and then the left ventricle. In case of sale of your personal information, you may opt out by using the link Do not sell my personal information. Cookies Policy. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. Out of these cookies, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website.
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This category only includes cookies that ensures basic functionalities and security features of the website. All leads of the ECG record the same electrical impulses of the heart muscle. Diagnosis of arrhythmias may be made easier by examination of different leads. The lead ECG tracing is standard. Six leads are recorded by placing wires on each limb. The other six leads are recorded by placing wires on the chest in six specific positions. Chest Leads: , , , , ,. For diagnosis of most arrhythmias, lead II is most commonly used.
Lead II and the chest leads most consistently show the most clear P Wave which can be diagnostic of many common arrhythmias. If changes in the ECG tracing are seen in a group of the above leads, the disease can be localized to a particular area of the heart. If the MD can thus localize the damage to the heart they can also diagnose other possible problems in the heart. Valvular problems may show up as a specific change in one or more leads of the ECG tracing.
Blockages in one of the major arteries of veins may also show up as an altered deflection in the ECG. Below is a diagram of the chest and the placement of leads of the chest so as to trace leads I and II. When the patient is being monitored for a specific arrhythmia, it will help to connect the wires to the spot of the chest that will show that arrhythmia most clearly.
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