Basics of ECG PDF

Basics of ECG  Electrocardiography (ECG or EKG) Electrocardiography (ECG or EKG) is a quick, simple, painless procedure in which the heart’s electrical impulses are amplified and recorded. ECG is a diagnostic tool that is routinely used to assess...

Basics of ECG  Electrocardiography (ECG or EKG) Electrocardiography (ECG or EKG) is a quick, simple, painless procedure in which the heart’s electrical impulses are amplified and recorded. ECG is a diagnostic tool that is routinely used to assess the electrical and muscular functions of the heart as well as provide indirect evidence of blood flow to the heart muscle. ECG also can measure the rate and rhythm of the heartbeat.  ECG procedure To obtain an ECG, an examiner places electrodes (small round sensors that stick to the skin) on the person's arms, legs, and chest. These patches are connected to an ECG machine that records the tracings and prints them onto paper. Ten electrodes are needed to produce 12 electrical views of the heart. Four electrode lead, or patch, are placed on each arm and leg (limb leads) and six are placed across the chest wall (chest leads). The signals received from each electrode are recorded. The printed view of these recordings is the electrocardiogram.  Parts of an ECG The standard ECG has 12 leads. Six of the leads are considered “limb leads” because they are placed on the arms and/or legs of the individual. The other six leads are considered “precordial leads” because they are placed on the torso (precordium). The six limb leads are called lead I, II, III, aVL, aVR and aVF. The letter “a” stands for “augmented,” as these leads are calculated as a combination of leads I, II and III. The six precordial leads are called leads V1, V2, V3, V4, V5 and V6. Diagrammatic representation of an ECG complex The vertical axis represents amplitude in millivolts (10mm=1millivolt). The horizontal scale represents time (5mm=0.20second, 1mm=0.04 second). How to Read an ECG Strip ECG paper is a grid where time is measured along the horizontal axis. Each small square is 1 mm in length and represents 0.04 seconds. Each larger square is 5 mm in length and represents 0.2 seconds. Voltage is measured along the vertical axis. 10 mm is equal to 1mV in voltage.  ECG Interpretation (parts of the ECG) P waves P waves represent atrial depolarization. In healthy individuals, there should be a P wave preceding each QRS complex QRS complex The QRS complex represents depolarization of the ventricles. It appears as three closely related waves on the ECG (the Q, R and S wave) T wave The T wave represents ventricular repolarization. It appears as a small wave after the QRS complex PR interval The PR interval begins at the start of the P wave and ends at the beginning of the Q wave. It represents the time taken for electrical activity to move between the atria and the ventricles. ST segment The ST segment starts at the end of the S wave and ends at the beginning of the T wave. The ST segment is an isoelectric line that represents the time between depolarization and repolarization of the ventricles (i.e. ventricular contraction).  The ECG records the heart tracing in12 leads: Six limb leads (I, II, III, AVR, AVL, AVF) and six chest leads (V1-V6). The P wave looks at the atria. The QRS complex looks at the ventricles and the T wave evaluates the recovery stage of the ventricles while they are refilling with blood. The time it takes for electricity to travel from the SA node to the AV node is measured by the PR interval. The QRS interval measures electrical travel time through the ventricles and the QT interval measures how long it takes for the ventricles to recover and prepare to beat again. Basic P-QRS-T wave sequence: Strip shows a simple sequence where M equals 1.0 millivolts.