The Electrocardiogram part II. Dr. Adelina Vlad, MD PhD

Transcription

1 The Electrocardiogram part II Dr. Adelina Vlad, MD PhD

2 Basic Interpretation of the ECG 1) Evaluate calibration 2) Calculate rate 3) Determine rhythm 4) Determine QRS axis 5) Measure intervals 6) Analyze the morphology and interrelation of ECG elements (P, P-Q, Q, QRS, ST, T, QT) in frontal and in precordial leads OR 6) Asses for Hypertrophy 7) Look for evidence of Infarction

3 1) Voltage and Time Calibration Vertically One small box mv Two large boxes 1mV Horizontally One small box s One large box s

4 The direct method 2) Calculate Rate Heart rate = nr. heart beats / min = 60 s/ duration of cardiac cycle One cardiac cycle measures the number of seconds between waves of the same type, for example, the R-R interval R R = 16 x 0.04 = 0.64 Rate = 60/ 0.64 = 94 beats/min

5 Calculate Rate R wave The quick method Find a R wave that lands on a bold line Count the number of large boxes to the next R wave. If the second R wave is 1 large box away the rate is 300, 2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc. (cont) A bit less than 100 beats/min 94 beats/min

6 3) Rhythm Analysis Questions to be answered for assessing the heart rhythm: Where is the heart s pacemaker? What is the conduction path from the pacemaker to the last cell in the ventricles? Is the pacemaker functioning regularly and at the correct rate?

7 Step 1: Step 2: Step 3: Step 4: Step 5: Calculate rate Determine regularity Assess the P waves Determine PR interval Determine QRS duration

8 Step 2: Determine regularity R R Look at the R-R distances (using a caliper or markings on a pen or paper) Regular (are they equidistant apart)? Occasionally irregular? Regularly irregular? Irregularly irregular? Interpretation? Regular

9 Step 3: Assess the P waves Are there P waves? Do the P waves all look alike and have the normal polarity? Do the P waves occur at a regular rate? Is there one P wave before each QRS? Interpretation? Normal P waves with 1 P wave for every QRS

10 Step 4: Determine PR interval Normal: seconds. (3-5 boxes) Interpretation? 0.12 seconds

11 Step 5: QRS duration Normal: seconds (1-3 boxes) Interpretation? 0.08 seconds

12 Rhythm Summary Rate Regularity P waves PR interval QRS duration bpm regular normal 0.12 s 0.08 s Interpretation? Normal Sinus Rhythm

13 NSR Parameters Rate Regularity P waves PR interval QRS duration bpm regular normal s s Any deviation from above is sinus tachycardia, sinus bradycardia or an arrhythmia

14 4) Determine QRS Axis (The Electrical Axis of the Heart) Is the axis of the mean force during ventricular activation, measured in the frontal plane = mean QRS vector in the frontal plane Equals the sum of instantaneous activation vectors (corresponding to septum, apex, free walls and base activation)

15 It is estimated by analyzing QRS complexes in two leads of the frontal plane Two approaches can be used The geometric method, accurate but more elaborate The inspection method, quicker and easier, sufficiently accurate for clinical purposes

16 1 Measure magnitude of QRS 5 Estimate axis of yellow arrow (about 95 ) Geometric Method

17 Each wave of the QRS complex in a lead represents the projection of a momentum ventricular activation vector on that lead The algebraic sum of the amplitudes of QRS waves in a limb lead represents the projection of the mean ventricular activation vector (mean QRS vector or QRS axis) on the axis of that specific lead Perpendiculars raised from the peak of mean QRS projections on the axis of two limb leads (draw as part of the hexaxial reference system) will cross each other in a point that marks the peak of the mean QRS vector By connecting the center of the hexaxial reference system (tail of vector) to the intersection of the two perpendicular lines (head of vector) it will result the image of the QRS axis, with its orientation; normal values: between -30 and +90 degrees

18 Inspection Method

19 The QRS axis is perpendicular to the limb lead with a null or very small QRS net amplitude; an equidiphasic complex has the net amplitude 0, no matter how large the RS waves are The QRS axis is parallel to the limb lead with the highest QRS net amplitude The two limb leads mentioned above should be perpendicular to one another

20 +50

21 +30

22 If there is no lead with a QRS net amplitude zero or close to zero, find two leads separated by a 30 angle, onto which the QRS are of maximal and similar magnitude The QRS axis is oriented half way between those two leads +15

23 0

24 +120

25 Normal and Abnormal QRS Axis The normal QRS axis lies between -30 o and +90 o. A QRS axis that falls between -30 o and -90 o is abnormal and called left axis deviation o -120 o o -90 o -60 o -30 o A QRS axis that falls between +90 o and +150 o is abnormal and called right axis deviation. 180 o 150 o 30 o 0 o A QRS axis that falls between +150 o and -90 o is abnormal and called superior right axis deviation. 120 o o 90 o 60 o

26 Left Axis Deviation Left axis deviation in a hypertensive heart (hypertrophic left ventricle). Note the slightly prolonged QRS complex as well. Left axis deviation caused by left bundle branch block. Note also the greatly prolonged QRS complex.

27 Right Axis Deviation High-voltage electrocardiogram in congenital pulmonary valve stenosis with right ventricular hypertrophy. Superior right axis deviation and a slightly prolonged QRS complex also are seen. Right axis deviation caused by right bundle branch block. Note also the greatly prolonged QRS complex.

28 5) Calculate Intervals Intervals refers to the length of the PR and QT intervals and the width of the QRS complexes PR interval < 0.12 s s > 0.20 s High catecholamine states Wolff-Parkinson-White Normal AV nodal blocks Wolff-Parkinson-White 1st Degree AV Block

29 QRS complex < 0.10 s s > 0.12 s Normal Incomplete bundle branch block Bundle branch block PVC Ventricular rhythm Incomplete bundle branch block 3 rd degree AV block with ventricular escape rhythm

30 QTc interval < 0.44 s > 0.44 s Long QT Normal Long QT Torsades de Pointes A prolonged QT can be very dangerous. It may predispose an individual to a type of ventricular tachycardia called Torsades de Pointes. Causes include drugs, electrolyte abnormalities, CNS disease, post-mi, and congenital heart disease.

31 QT = 0.40 s RR = 0.68 s Square root of RR = 0.82 QTc = 0.40/0.82 = 0.49 s PR interval? QRS width? QTc interval? 0.16 seconds 0.08 seconds 0.49 seconds Interpretation of intervals? Normal PR and QRS, long QT

32 RR 23 boxes 17 boxes 10 boxes QT 13 boxes Normal QT Long QT QTc = QT/ RR Tip: Instead of calculating the QTc, a quick way to estimate if the QT interval long is to use the following rule: A QT > half of the RR interval is probably long

33 6) Hypertrophy The ECG can reveal enlargement or hypertrophy of the four chambers of the heart: Right atrial enlargement (RAE) Left atrial enlargement (LAE) Right ventricular hypertrophy (RVH) Left ventricular hypertrophy (LVH)

34 Ventricular Hypertrophy Due to a pressure or volume load ECG abnormalities High voltage R, S waves QRS axis deviation Increased intrinsecoid deflection T-wave inversions

35 7) Look for Evidence of Infarction When analyzing a 12-lead ECG for evidence of an infarction one looks for the following: Abnormal Q waves ST elevation or depression Peaked, flat or inverted T waves ST elevation (or depression) in at least two leads is the earliest and most consistent ECG finding during AMI There are ST elevation (Q-wave) and non-st elevation (non-q wave) MIs

36 ST Elevation Elevation of the ST segment in at least 2 leads is consistent with a myocardial infarction Because blood flow is regional, the area of infarction are also regional specific ECG leads can provide the best view of the infarcted area

37 Views of the Heart Some leads get a good view of the: Anterior portion of the heart Leads V1 V4 Lateral portion of the heart Leads I, avl, V5, V6 Inferior portion of the heart Leads II, III, avf

38 Anterior Wall MI Can be recognized if there are changes in leads V 1 - V 4 that are consistent with a myocardial infarction

39 Inferior Wall MI ST segment is elevated in leads II, III and avf

40 Anterolateral MI This person s MI involves both the anterior wall (V 2 -V 4 ) and the lateral wall (V 5 -V 6, I, and avl)!

41 8) Others Drug effects (digitalis, class 1 and 3 antiarrhythmic agents, psychotropic drugs etc.) Electrolyte and metabolic abnormalities (Ca, K, Mg, ph etc.) Etc

42 Specialized ECG Tests Additional precordial leads help diagnose right ventricular and posterior wall MI (V1R V6R; V8, V9) Esophageal lead for better recording atrial activity or to monitor intraoperative myocardial ischemia Holter monitoring continuous monitoring and recording of the ECG, blood pressure or both for h; ECG evaluates intermittent arrhythmias Event recordings up to 30 days, can detect infrequent rhythm disturbances that a Holter monitoring may miss; the recorder is activated by the patient when symptoms occur Continuous ST-segment monitoring early detection of ischemia and serious arrhythmias (emergency unit, intraoperative monitoring, postoperative care)