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Effect of right atrial enlargement. P mitrale. Effect of left atrial enlargement. P biatrial combination of P mitrale and P pulmonale. Effect of biatrial enlargement. References: [11].

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Patients with ventricular hypertrophy may not exhibit these signs on their ECG: These may become apparent later in the course of the disease or they may even be absent in some cases e. However, ECG changes associated with clinical signs confirm the diagnosis of hypertrophy! References: [12] [13]. References: [14] [15]. A new pathological Q wave represents myocardial infarction until proven otherwise!

References: [16] [17]. Associated with Brugada syndrome : rare autosomal dominant condition that affects sodium channels and disturbs repolarization. ST elevation from a descending R is likely caused by a myocardial infarction! References: [18] [19] [20] [21] [22] [23] [24] [25] [26]. The stages of myocardial ischemia are associated with characteristic but variable ECG findings:. References: [23].

New occurrence of a left bundle branch block associated with angina chest pain is defined as a STEMI! References: [27] [28] [29]. References: [5] [30] [31] [32]. Clinical science Electrocardiography ECG is an important diagnostic tool in cardiology. Holter monitor Definition : A continuous, ambulatory battery operated ECG worn by patients for hours Indications Daily or near-daily symptoms of: Syncope Palpitations Patients who are unable to use other ambulatory ECG monitoring devices Assessing effect of new atrial fibrillation rate control medication e.

When interpreting an ECG, it is important to keep the individual patient in mind and, if possible, to compare it with previous ECGs. A thorough, algorithmic approach to ECG interpretation that assesses every aspect of the ECG ensures that no abnormalities are overlooked. Determination of the heart rate The heart rate i. The atrial rate is sometimes calculated e. Implementation If the QRS rhythm is regular see determination of the heart rhythm below , then the heart rate can be estimated by dividing by the number of large 5 mm squares between successive QRS complexes , or by counting the number of QRS complexes in 6 seconds and multiplying by This method is only a rough estimate.

This method of measuring the heart rate is not very precise and only for initial orientation. Implementation P wave assessment Are they visible in any lead? Determine the atrial rate i. Determine the morphology of the P waves. If not present: Determine the atrial and ventricular heart rates. Is there an abnormal number of P waves compared to QRS complexes? QRS morphology Normal duration: 0. Like all medical tests, what constitutes "normal" is based on population studies.

The heartrate range of between 60 and beats per minute bpm is considered normal since data shows this to be the usual resting heart rate. Interpretation of the ECG is ultimately that of pattern recognition. In order to understand the patterns found, it is helpful to understand the theory of what ECGs represent.

The theory is rooted in electromagnetics and boils down to the four following points:. Thus, the overall direction of depolarization and repolarization produces a vector that produces positive or negative deflection on the ECG depending on which lead it points to. For example, depolarizing from right to left would produce a positive deflection in lead I because the two vectors point in the same direction. In contrast, that same depolarization would produce minimal deflection in V 1 and V 2 because the vectors are perpendicular and this phenomenon is called isoelectric.

Normal rhythm produces four entities — a P wave, a QRS complex, a T wave, and a U wave — that each have a fairly unique pattern. However, the U wave is not typically seen and its absence is generally ignored. Changes in the structure of the heart and its surroundings including blood composition change the patterns of these four entities.

ECGs are normally printed on a grid. The horizontal axis represents time and the vertical axis represents voltage. The standard values on this grid are shown in the adjacent image:. The "large" box is represented by a heavier line weight than the small boxes. Not all aspects of an ECG rely on precise recordings or having a known scaling of amplitude or time. For example, determining if the tracing is a sinus rhythm only requires feature recognition and matching, and not measurement of amplitudes or times i.

An example to the contrary, the voltage requirements of left ventricular hypertrophy require knowing the grid scale. In a normal heart, the heart rate is the rate in which the sinoatrial node depolarizes since it is the source of depolarization of the heart.

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Heart rate, like other vital signs such as blood pressure and respiratory rate, change with age. In adults, a normal heart rate is between 60 and bpm normocardic , whereas it is higher in children. A complication of this is when the atria and ventricles are not in synchrony and the "heart rate" must be specified as atrial or ventricular e.

In normal resting hearts, the physiologic rhythm of the heart is normal sinus rhythm NSR.

Generally, deviation from normal sinus rhythm is considered a cardiac arrhythmia. Thus, the first question in interpreting an ECG is whether or not there is a sinus rhythm. Once sinus rhythm is established, or not, the second question is the rate. For a sinus rhythm, this is either the rate of P waves or QRS complexes since they are 1-to If the rate is too fast, then it is sinus tachycardia , and if it is too slow, then it is sinus bradycardia.

If it is not a sinus rhythm, then determining the rhythm is necessary before proceeding with further interpretation. Some arrhythmias with characteristic findings:. The heart has several axes, but the most common by far is the axis of the QRS complex references to "the axis" imply the QRS axis. Each axis can be computationally determined to result in a number representing degrees of deviation from zero, or it can be categorized into a few types.

The QRS axis is the general direction of the ventricular depolarization wavefront or mean electrical vector in the frontal plane. It is often sufficient to classify the axis as one of three types: normal, left deviated, or right deviated. The normal QRS axis is generally down and to the left , following the anatomical orientation of the heart within the chest.

An abnormal axis suggests a change in the physical shape and orientation of the heart or a defect in its conduction system that causes the ventricles to depolarize in an abnormal way. All of the waves on an ECG tracing and the intervals between them have a predictable time duration, a range of acceptable amplitudes voltages , and a typical morphology. Any deviation from the normal tracing is potentially pathological and therefore of clinical significance.

It may also affect the high frequency band of the QRS. The earliest sign is hyperacute T waves, peaked T waves due to local hyperkalemia in ischemic myocardium. Over a period of hours, a pathologic Q wave may appear and the T wave will invert. Over a period of days the ST elevation will resolve.

Basic ECG Theory, Recordings, and Interpretation

Pathologic Q waves generally will remain permanently. The left anterior descending LAD artery supplies the anterior wall of the heart, and therefore causes ST elevations in anterior leads V 1 and V 2. An ECG tracing is affected by patient motion. Some rhythmic motions such as shivering or tremors can create the illusion of cardiac arrhythmia.

Electrocardiography - Wikipedia

Distortion poses significant challenges to healthcare providers, [37] who employ various techniques [39] and strategies to safely recognize [40] these false signals. Improper lead placement for example, reversing two of the limb leads has been estimated to occur in 0.

9 Steps to ECG Interpretation

Numerous diagnoses and findings can be made based upon electrocardiography, and many are discussed above. Overall, the diagnoses are made based on the patterns. For example, an "irregularly irregular" QRS complex without P waves is the hallmark of atrial fibrillation ; however, other findings can be present as well, such as a bundle branch block that alters the shape of the QRS complexes.

ECG 2 - P,Q,R,S & T Waves