Left axis deviation occurs if lead I is positive and II is negative. Right axis deviation is negative in I and positive in II. Left axis deviation may occur in left ventricular hypertrophy (LVH), along with ST depression in lateral leads. Right axis deviation occurs in situations where there is right heart strain, such as pulmonary embolisms and atrial septal defect.

Left axis deviation (LAD) involves the direction of depolarisation being distorted to the left (between -30° and -90°). This results in the deflection of lead III becoming negative (this is only considered significant if the deflection of lead II also becomes negative). Conduction abnormalities usually cause left axis deviation. Left Axis Deviation (LAD) The QRS Complex (0.3 secs) – this is the ventricles contracting, so once again, any abnormalities that form in the QRS complex would represent an issue with the two lower chambers. RAD is commonly associated with conditions such as pulmonary hypertension, as they cause right ventricular hypertrophy. RAD can, however, be a normal finding in very tall individuals. Right Axis Deviation Left axis deviation

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Heart failure, COPD, thyrotoxicosis, constrictive pericarditis, ischemic heart disease, sepsis, pulmonary embolus, rheumatic heart disease, hypertension, mitral stenosis, atrial irritation, complication of coronary bypass or valve replacement surgery In healthy individuals, the electrical activity of the heart begins at the sinoatrial node then spreads to the atrioventricular (AV) node. It then spreads down the bundle of His and Purkinje fibres to cause ventricular contraction. When electrical activity (or depolarisation) travels towards a lead, the deflection is net positive. When the activity travels away from the lead the deflection is net negative. If it is at 90 degrees then the complex is ‘isoelectric’ i.e. the R and S wave are the same size. This can often be seen in V4 (see Figure 3). EKG/ECG proficiency is required for many nursing jobs. Telemetry, cardiac, and stepdown units all require some level of proficiency. Nurses interested in working in the intensive care unit or cardiac care unit are required to be proficient in reading EKGs. These jobs are also in high demand. The ECG can be broken down into the individual components. For the purpose of this we will look at lead II (see Figure 4). All boxes are based on the assumption that the paper speed is running at 25mm/sec, therefore 1 large square is equivalent to 0.2 secs and a small square to 0.04 secs.

PR interval: Represents the time taken for excitation to spread from the sino-atrial (SA) node across the atrium and down to the ventricular muscle via the bundle of His. Can you see a p-wave? If the rhythm is atrial fibrillation, atrial flutter or a junctional tachycardia you may not be able to. Each deflection (a.k.a. wave) on the ECG represents the average direction of electrical travel (calculated using the ECG machine’s mathematical formulae).

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Count the number of QRSs on one line of the ECG (usually lead II – running along the bottom) and multiply by six. This is not always easy for busy physicians. This article outlines a few pitfalls for the non-specialist ECG interpreter. Do the R waves increase gradually and normally across the chest leads (the R wave should be bigger than the S wave by V4)?

Right axis deviation (RAD) involves the direction of depolarisation being distorted to the right (between +90º and +180º). When confronted with an ECG it is best to start with the basics: rate, rhythm and axis. Then consider the PQRST complexes in all the leads with some basic questions in mind: So how do we perform a 12 lead ECG? There are 10 electrodes: 6 precordial; these are the chest leads commonly known as the ‘V’ leads and 4 extremity electrodes, commonly known as the limb leads. Let’s start with the limb leads as these can also be used to perform a 3 lead ECG. Whenever the direction of electrical activity moves towards a lead, a positive deflection is produced. Rhythm can be difficult to assess especially in bradycardia or tachycardia. It may be helpful to use the ‘paper test’.Observe the distribution of the T wave inversion (e.g. anterior/lateral/posterior leads). You must take this ECG finding and apply it in the clinical context of your patient. Inverted T wave Biphasic T waves The more familiar you are with different rhythms, the easier interpretation becomes. Don’t forget your colleagues are great resources as well; let them know you are working on your 12 lead EKG interpretation skills and ask them to save interesting tracings for your review. When the electrical activity within the heart travels towards a lead, you get a positive deflection.