Cardio P4 ECG 2 PDF

Cardiovascular Block The Electrocardiogram 2 Dr Simon Harrison [email protected] Room S3-76 1 Good sources: http://ww...

Cardiovascular Block The Electrocardiogram 2 Dr Simon Harrison [email protected] Room S3-76 1 Good sources: http://www.practicalclinicalskills.com Good resource: https://www.youtube.com/watch?v=9TRYM7IdnDY Fun You-tube video of cardiac dysrhythmias: http://youtu.be/x5oq4ErAmW0 Suggested reading: 1  Introduction to the ECG 2 - Learning Objectives 11. Determine parameters from a typical ECG tracing: e.g. heart rate, P-R interval and segment, Q- T interval, QRS duration, T-P interval and correlate these with electrical events at the level of the heart such e.g. AV conduction time, duration of ventricular depolarization and of diastole and systole. 12. Identify the ECG traces produced by each of the following: sinus tachycardia and bradycardia, LQTS, AV blocks (1st, 2nd, 3rd degree), junctional rhythm, atrial and ventricular fibrillation. 13. Identify the rhythm of ECG traces (regular, regularly irregular, irregularly irregular) and how to systematically read an ECG trace. Identify the ECG changes associated with an inferior myocardial infarction and how the 12 leads are grouped together. 14. Define mean electrical axis of the heart and give the normal range (+90 to -30 degrees). 15. Correlate changes in the mean electrical axis with alterations in ventricular size caused by left and right ventricular hypertrophy. 16. Determine the direction of the mean electrical axis using the net direction of QRS complexes in the six limb leads (semi-quantitative method) and the net zero lead method. 17. Estimate the mean electrical axis using the net direction of QRS complexes in Lead I and aVF to determine right/left axis deviation and correlate with causes of right and left axis deviation. 2 Excellent ECG resource : http://en.ecgpedia.org/wiki/Main_Page 2  ECG trace paper is standardized worldwide 0.2 sec = 5 mm 0.04 sec = 1 mm 0.1 mV = 1 mm 0.5 mV = 5 mm Height of the QRS: Sokolow-Lyon Criteria V1 depth plus V5/6 height >35 mm (7 big boxes) signals LVH Time (sec)- 25 mm/sec = paper speed LO11 3 An ECG trace can be used to calculate heart rate and the duration (length) of events during an ECG. The divisions marked on ECG paper are standardized. Along the vertical axis (voltage), the distance between two major divisions equals 0.5 mV. Along the horizontal axis (time), each little box on an ECG trace corresponds to 0.04 seconds, and the bigger boxes correspond to 0.2 seconds. The most common way to measure heart rate from an ECG recording is to count the small boxes between two R-waves. What does the height of the QRS complex tell us? The more aligned the spread of depolarization is with a particular vector the greater the height of the QRS on that lead. To explain further for a normal heart, if the spread of depolarization is directly towards the positive electrode of lead II, then the QRS complex will be the most positive on that lead. So, taking this a step further, if Lead II is the strongest positive, the QRS on leads I and III will also be positive but less so. Further if ventricular mass increases- let’s say the left ventricle, then for the larger mass, a greater signal will be generated. Therefore, in a condition like left ventricular hypertrophy (enlargement) the height of the QRS complexes will be increased compared to a normal heart. Increased QRS voltage is often taken to infer the presence of left ventricular hypertrophy. However, high left ventricular voltage (HLVV) may be a normal finding in patients less than 40-45 years of age, particularly slim or athletic individuals. There are multiple “voltage criteria” for left ventricular hypertrophy. Probably the most commonly used are the Sokolow-Lyon criteria (S wave depth in V1 + tallest R wave height in V5-V6 > 35 mm or 3.5 mV, 7 big boxes). The QRS is said to be low voltage when: The amplitudes of all the QRS complexes in the limb leads are < 5 mm (0.5 mV 1 big box); or The amplitudes of all the QRS complexes in the precordial leads are < 10 mm (1.0 mV, 2 big boxes). 3  Calculate Heart Rate from an ECG R R paper speed = 25 mm/s 20 x 0.04 sec = 0.80 seconds per beat (60 seconds/minute) / (0.80 seconds/beat) = 75 bpm Exact measure of heart rate: Determine time interval between successive heart beats (R-R interval). Time interval divided into 60 sec/min = HR (bpm) 4 Exact calculation of Heart Rate from an ECG trace: On the trace above, there are approximately 20 boxes between two R-waves: 20 x 0.04 sec = 0.8 seconds per heart beat (cardiac period) If one heartbeat takes 0.80 sec., then the number of heartbeats per minute would be: (60 seconds/minute) / (0.8 seconds/beat) = 75 beats/minute 4  Estimate Heart Rate from an ECG Quick estimate of heart rate 300 150 100 75 60 50 43 R R 0.2 0.4 0.6 0.8 1.0 1.2 1.4 OR 300/4 = 75 bpm 5 Estimation of Heart Rate from an ECG trace: 1. On the trace above, choose one R-wave and draw a vertical line through it. 2. Count over 5 small boxes on the trace and draw another vertical line. If the next R wave is here, the heart rate is 300 BPM. If the next R-wave is not here, repeat this step for each big box (0.2 s) 3. If the next R wave occurs after 2 big boxes the heart rate is 150 BPM. 4. The sequence of Heart Rates is: 300, 150, 100, 75, 60, 50, 43, 37 BPM for 1, 2 ,3, 4, 5, 6, 7, 8 big boxes, respectively So if the R-R interval is within 4 or 5 big boxes that is within normal limits for HR (between 100 and 60 bpm). Another way is to just use the big boxes each of which represent 0.2 seconds. If you count the big boxes between R waves - lets say it is 4 big boxes, then you divide 300 by the number of big boxes, i.e. 300/4 = 75. If is 3.5 big boxes then divide 300 by 3.5 so 300/3.5 = 86 beats per min. 5  Calculate Intervals from an ECG R-R interval =.80 s R R QRS complex PR Interval QT Interval 1.5 sm boxes 4 sm boxes 8 sm boxes 0.06 s 0.16 s 0.32 s PR interval should be 0.12 – 0.20 seconds QRS complex should be less than 0.10 seconds QT interval is generally less than 0.4 s at rest (QTc=0.36).LO11 6 To calculate the time duration of a segment or interval. 1. Count the number of small boxes that makeup the duration of the interval/segment that you want to measure. 2. Multiple the number of small boxes by 0.04 sec. 3. The answer is the time duration of that segment/interval. 4. QTc = 0.32 /root 0.8 = 0.36s 6  What does the Mean Electrical Axis tell us? The net direction of electrical conduction during ventricular depolarization. Indicates: – Orientation of heart – Size of ventricular chambers – Conduction block LO14 7 The MEA tells us the net direction of electrical conductance during ventricular depolarization. It can indicate several things, such as the orientation of the heart, the size of the ventricles, and conduction blocks. The three standard limb leads (I, II, III) can be viewed as forming an equilateral triangle (Einthoven’s triangle) in the frontal plane with the heart at its center. The angles of an equilateral triangle are each 60o so each standard limb lead represents a point on a circle that is 60o away from the previous limb lead. The horizontal lead, Lead I, forms the 0o – 180o line and all other leads are positioned relative to Lead I. The augmented limb leads (aVR, aVL, aVF) bisect each of the angles of the triangle so they fall on the circle, halfway between each standard limb lead as shown in the figure above. The arrowhead in each case represents the positive electrode in each of the leads. Using this radial projection of the six limb leads, the mean electrical axis of the heart can be determined. As indicated previously, the general direction of conduction through the heart is from upper right to lower left on the body. The mean electrical axis of the heart can be thought of as a vector or arrow pointing down and to the left on the body (or from left and downwards to the right on the diagram above (i.e. from -120 to +60 above). By using the size and direction of the QRS complex in each lead, the mean electrical axis can be determined. 7  Interpreting changes in the MEA Normal axis = +900 to -300 Left axis deviation = -300 to -900 Commonly seen in any condition causing left ventricular hypertrophy, inferior STEMI Right axis deviation = +900 to +1800 Normal finding in children and tall thin adults Commonly seen in any condition causing right ventricular hypertrophy Extreme axis deviation+1800 to -900 Lateral STEMI, COPD, Dextrocardia LO15 8 A mean electrical axis from +90 to -30 degrees is considered normal. (NOTE: some sources state +90 to 0 degrees as within the normal range) A left heart axis is present when the QRS in lead I is positive, weakly positive or negative in lead II and negative in AVF. (between -30 and -90 degrees) A right heart axis is present when lead I is negative and AVF positive. (between +90 and +180) An extreme heart axis is present when both I and AVF are negative. (axis between +180 and -90 degrees). This is a rare finding. Some possible causes of left axis deviation include: Left ventricular hypertrophy inferior myocardial infarction Emphysema. This is caused by displacement of the heart posteriorly, by the hyper-expanded emphysematous lungs thus the left ventricle and therefore the MEA move into the upper right quadrant Some possible causes of right axis deviation include: normal finding in children and tall thin adults right ventricular hypertrophy chronic lung disease with pulmonary hypertension pulmonary embolus 8  Three ways to determine the MEA 1. Semi-Quantitative Method: from the net direction of QRS complexes of all six limb leads. 2. Net Zero Lead Method: can use if a lead has a net zero QRS complex (or very close to net zero). 3. Quadrant Method: from the net direction of QRS complexes in Leads I and aVF. LO16 9 Determining the MEA is all about interpreting the direction of the QRS complexes in the 6 frontal leads. If the QRS is more positive than negative it is called net positive. If the negative deflection is greater than the positive deflection- net negative. If both positive and negative deflections are the same, this is called net zero, isoelectric or eqiphasic. 9  1. Semi-Quantitative Method Arrow Heads denote the +ve electrodes LO16 10 Semi-quantitative method: estimating the MEA from the net direction of QRS complexes in the six limb leads. 1. Draw a radial axis 2. Determine if the QRS complex is net positive or net negative for Lead I. 3. If the QRS complex is net positive put a dot on the positive side of lead I on the radial axis. If the QRS complex is net negative, put a dot on the negative side of lead I on the radial axis. 4. On the radial axis, draw a 90 degree arc (three segments) in each direction from the dot. It is best to do this as close to the center of the radial axis to give room for all the other arcs to be drawn. 5. Repeat each of these steps for Leads II, III, aVR, aVL and aVF effectively drawing concentric semicircles around the radial axis- one for each lead. 6. Find the 30 degree segment where there are the most overlapping lines and that is the range in which the patients MEA will be found. 7. In this case the MEA lies between +60 and +90 and therefore is normal. 10  2. Net Zero Lead Method: Arrow Heads denote the +ve electrodes LO16 11 Net Zero Lead Method: If there is a net zero lead on the ECG trace (see Lead III), then you can easily determine the MEA of the person. 1. Determine if any lead has net zero QRS complex (positive and negative deflection is approximately equal). In this case lead 3 is net zero. 2. Find the lead that is exactly perpendicular (90 degrees or three segments) from the net zero lead. In this case that is the +30 position or -150 of the aVR lead. One of the ends of this lead (positive or negative) will be the MEA of the person. 3. Look at the QRS complex of the perpendicular lead. If the QRS complex is net positive, then the positive end of the lead is the person’s MEA; if it is net negative, then the negative end of the lead will be the MEA. In this case the aVR lead has a negative QRS and so the MEA of the individual is the negative aVR direction, i.e. +30 and therefore normal. 11  3. Quadrant method: From the net direction of QRS complexes in Leads I & aVF. Normal MEA Lead I = + Lead aVF = + Right Axis Deviation Lead I = - Lead aVF = + Left Axis Deviation Lead I = + LO17 12 Arrow Heads denote the +ve electrodes Lead aVF = - Right and left axis deviation can be determined by examining the QRS complexes in Lead I and aVF. This method places the MEA in any of the three sectors of Normal, left and right axis deviation. 12  Explaining QRS and MEA https://en.ecgpedia.org/index.php?title=QRS_axis 13 13  Irregularities in the ECG Normal Sinus Rhythm: 1:1 ratio between P, QRS and T waves (60-99 bpm). 300/3.6 = 83 bpm Junctional Rhythm: SA node non functional. Heart paced by AV node (40-60 bpm). Note inverted P waves. 300/5.6 = 54 bpm LO12 14 The identification of arrhythmias is complex requiring a thorough understanding of heart anatomy, the normal conduction pathways through the heart, and how subtle changes in the ECG trace reflect alterations in conduction. In this lecture we will include some common irregularities but this is by no means an exhaustive list and you will become familiar with other irregularities later in the course. A normal sinus rhythm indicates that the SA node is acting as the pacemaker of the heart. You should see: Rhythm - Regular Rate - (60-100 bpm) actually 83 bpm QRS Duration - Normal P Wave - Visible before each QRS complex P-R Interval - Normal (100 bpm at rest 300/2.4 = 125 bpm Sinus Bradycardia 28 sm boxes = 1.12 s = HR ~ 54 bpm 100 bpm) or reduced (bradycardia, < 60 bpm) it is called either sinus tachycardia or sinus bradycardia, respectively. The use of the word “sinus” indicates that the elevated or depressed rate originates within the sinoatrial node. Sinus tachycardia Looking at the ECG you'll see that: Rhythm – Regular Rate - More than 100 beats per minute QRS Duration – Normal (