Module 7b

ECG Rhythm Interpretation Module VII b Reading 12-Lead ECG’s

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Course Objective To systematically analyze a 12-lead ECG.

Learning Modules ECG Basics How to Analyze a Rhythm Normal Sinus Rhythm Heart Arrhythmias Diagnosing a Myocardial Infarction Advanced 12-Lead Interpretation Reading 12-Lead ECG’s

Reading 12-Lead ECGs In Module VII a we introduced a 6 step approach for analyzing a 12-lead ECG and covered the first 3 steps. In this module we will cover the last 3 steps. Calculate RATE Determine RHYTHM Determine QRS AXIS Calculate INTERVALS Assess for HYPERTROPHY Look for evidence of INFARCTION

Rate Rhythm Axis Intervals Hypertrophy Infarct Intervals refers to the length of the PR and QT intervals and the width of the QRS complexes. You should have already determined the PR and QRS during the “rhythm” step, but if not, do so in this step. In the following few slides we’ll review what is a normal and abnormal PR, QRS and QT interval. Also listed are a few common causes of abnormal intervals.

Rate Rhythm Axis Intervals Hypertrophy Infarct PR interval Wolff-Parkinson-White 1st Degree AV Block AV nodal blocks Normal High catecholamine states Wolff-Parkinson-White > 0.20 s 0.12-0.20 s < 0.12 s

Rate Rhythm Axis Intervals Hypertrophy Infarct QRS complex Remember: If you have a BBB determine if it is a right or left BBB. If you need a refresher see Module VI . 3 rd degree AV block with ventricular escape rhythm Incomplete bundle branch block Bundle branch block PVC Ventricular rhythm Incomplete bundle branch block Normal > 0.12 s 0.10-0.12 s < 0.10 s

Rate Rhythm Axis Intervals Hypertrophy Infarct QT interval The duration of the QT interval is proportionate to the heart rate. The faster the heart beats, the faster the ventricles repolarize so the shorter the QT interval. Therefore what is a “normal” QT varies with the heart rate. For each heart rate you need to calculate an adjusted QT interval, called the “corrected QT” (QTc): QTc = QT / square root of RR interval

Rate Rhythm Axis Intervals Hypertrophy Infarct QTc interval 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. Torsades de Pointes Long QT Long QT Normal > 0.44 s < 0.44 s

Rate Rhythm Axis Intervals Hypertrophy Infarct PR interval? QRS width? QTc interval? 0.08 seconds 0.16 seconds 0.49 seconds QT = 0.40 s RR = 0.68 s Square root of RR = 0.82 QTc = 0.40/0.82 = 0.49 s Interpretation of intervals? Normal PR and QRS, long QT

Rate Rhythm Axis Intervals Hypertrophy Infarct 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. Normal QT Long QT QT RR 10 boxes 23 boxes 17 boxes 13 boxes

Rate Rhythm Axis Intervals Hypertrophy Infarct In this step of the 12-lead ECG analysis, we use the ECG to determine if any of the 4 chambers of the heart are enlarged or hypertrophied. We want to determine if there are any of the following: Right atrial enlargement (RAE) Left atrial enlargement (LAE) Right ventricular hypertrophy (RVH) Left ventricular hypertrophy (LVH)

Rate Rhythm Axis Intervals Hypertrophy Infarct In Module VI we introduced the concept of left ventricular hypertrophy. As you remember the QRS voltage increases with LVH and is characterized by tall QRS complexes in certain leads. Similarly for right ventricular hypertrophy we look at the QRS complexes for changes in voltage patterns. With right and left atrial enlargement we analyze the P wave (since the P wave represents atrial depolarization). Here we also look for changes in voltage patterns. Note: as mentioned in Module VI criteria exists to diagnose LVH, the same goes for RAE, LAE and RVH. In the following slides we will be presenting criteria you can use. However other criteria exists and as a reference you might find it useful to carry a copy of Tom Evans’ ECG Interpretation Cribsheet .

Rate Rhythm Axis Intervals Hypertrophy Infarct Right atrial enlargement Take a look at this ECG. What do you notice about the P waves? The P waves are tall, especially in leads II, III and avF. Ouch! They would hurt to sit on!!

Rate Rhythm Axis Intervals Hypertrophy Infarct Right atrial enlargement To diagnose RAE you can use the following criteria: II P > 2.5 mm , or V1 or V2 P > 1.5 mm Remember 1 small box in height = 1 mm A cause of RAE is RVH from pulmonary hypertension. > 2 ½ boxes (in height) > 1 ½ boxes (in height)

Rate Rhythm Axis Intervals Hypertrophy Infarct Left atrial enlargement Take a look at this ECG. What do you notice about the P waves? The P waves in lead II are notched and in lead V1 they have a deep and wide negative component. Notched Negative deflection

Rate Rhythm Axis Intervals Hypertrophy Infarct Left atrial enlargement To diagnose LAE you can use the following criteria: II > 0.04 s (1 box) between notched peaks , or V1 Neg. deflection > 1 box wide x 1 box deep Normal LAE A common cause of LAE is LVH from hypertension.

Rate Rhythm Axis Intervals Hypertrophy Infarct Right ventricular hypertrophy Take a look at this ECG. What do you notice about the axis and QRS complexes over the right ventricle (V1, V2)? There is right axis deviation (negative in I, positive in II) and there are tall R waves in V1, V2.

Rate Rhythm Axis Intervals Hypertrophy Infarct Right ventricular hypertrophy Compare the R waves in V1, V2 from a normal ECG and one from a person with RVH. Notice the R wave is normally small in V1, V2 because the right ventricle does not have a lot of muscle mass. But in the hypertrophied right ventricle the R wave is tall in V1, V2. Normal RVH

Rate Rhythm Axis Intervals Hypertrophy Infarct Right ventricular hypertrophy To diagnose RVH you can use the following criteria: Right axis deviation , and V1 R wave > 7mm tall A common cause of RVH is left heart failure.

Rate Rhythm Axis Intervals Hypertrophy Infarct Left ventricular hypertrophy Take a look at this ECG. What do you notice about the axis and QRS complexes over the left ventricle (V5, V6) and right ventricle (V1, V2)? There is left axis deviation (positive in I, negative in II) and there are tall R waves in V5, V6 and deep S waves in V1, V2. The deep S waves seen in the leads over the right ventricle are created because the heart is depolarizing left, superior and posterior (away from leads V1, V2).

Rate Rhythm Axis Intervals Hypertrophy Infarct Left ventricular hypertrophy To diagnose LVH you can use the following criteria * : R in V5 (or V6) + S in V1 (or V2) > 35 mm , or avL R > 13 mm A common cause of LVH is hypertension. * There are several other criteria for the diagnosis of LVH. S = 13 mm R = 25 mm

Rate Rhythm Axis Intervals Hypertrophy Infarct A 63 yo man has longstanding, uncontrolled hypertension. Is there evidence of heart disease from his hypertension? (Hint: There a 3 abnormalities.) Yes, there is left axis deviation (positive in I, negative in II), left atrial enlargement (> 1 x 1 boxes in V1) and LVH (R in V5 = 27 + S in V2 = 10  > 35 mm).

Rate Rhythm Axis Intervals Hypertrophy Infarct When analyzing a 12-lead ECG for evidence of an infarction you want to look for the following: Abnormal Q waves ST elevation or depression Peaked, flat or inverted T waves These topics were covered in Modules V and VI where you learned: ST elevation (or depression) of 1 mm in 2 or more contiguous leads is consistent with an AMI There are ST elevation (Q-wave) and non-ST elevation (non-Q wave) MIs

Rate Rhythm Axis Intervals Hypertrophy Infarct Tip: One way to determine if Q waves (and R waves) are abnormal is by looking at the width and using the following mantra (read red downwards): Any Any Q wave in V1 Any Any Q wave in V2 Any Any Q wave in V3 20 A Q wave > 20 msec in V4 (i.e. 0.02 sec or ½ width of a box) 30 A Q wave > 30 msec in V5 30 A Q wave > 30 msec in V6 30 A Q wave > 30 msec in I 30 A Q wave > 30 msec in avL 30 A Q wave > 30 msec in II 30 A Q wave > 30 msec in avF R40 A R wave > 40 msec in V1 R50 A R wave > 50 msec in V2

Rate Rhythm Axis Intervals Hypertrophy Infarct This mantra corresponds to the ECG in the following way: Any Any Any 20 30 30 30 30 30 30 R40 R50

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct To summarize: Calculate RATE Determine RHYTHM Determine QRS AXIS Normal Left axis deviation Right axis deviation Right superior axis deviation

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct To summarize: Calculate RATE Determine RHYTHM Determine QRS AXIS Calculate INTERVALS PR QRS QT

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct To summarize: Calculate RATE Determine RHYTHM Determine QRS AXIS Calculate INTERVALS Assess for HYPERTROPHY Right and left atrial enlargement Right and left ventricular hypertrophy

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct To summarize: Calculate RATE Determine RHYTHM Determine QRS AXIS Calculate INTERVALS Assess for HYPERTROPHY Look for evidence of INFARCTION Abnormal Q waves ST elevation or depression Peaked, flat or inverted T waves

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct To summarize: Calculate RATE Determine RHYTHM Determine QRS AXIS Calculate INTERVALS Assess for HYPERTROPHY Look for evidence of INFARCTION Now to finish this module lets analyze a 12-lead ECG!

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct A 16 yo young man ran into a guardrail while riding a motorcycle. In the ED he is comatose and dyspneic. This is his ECG.

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct What is the rate? Approx. 132 bpm (22 R waves x 6)

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct What is the rhythm? Sinus tachycardia

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct What is the QRS axis? Right axis deviation (- in I, + in II)

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct What are the PR, QRS and QT intervals? PR = 0.12 s, QRS = 0.08 s, QTc = 0.482 s

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct Is there evidence of atrial enlargement? No (no peaked, notched or negatively deflected P waves)

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct Is there evidence of ventricular hypertrophy? No (no tall R waves in V1/V2 or V5/V6)

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct Infarct: Are there abnormal Q waves? Yes! In leads V1-V6 and I, avL Any Any Any 20 30 30 30 30 30 30 R40 R50

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct Infarct: Is the ST elevation or depression? Yes! Elevation in V2-V6, I and avL. Depression in II, III and avF.

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct Infarct: Are there T wave changes? No

SUMMARY Rate Rhythm Axis Intervals Hypertrophy Infarct ECG analysis: Sinus tachycardia at 132 bpm, right axis deviation, long QT, and evidence of ST elevation infarction in the anterolateral leads (V1-V6, I, avL) with reciprocal changes (the ST depression) in the inferior leads (II, III, avF). This young man suffered an acute myocardial infarction after blunt trauma. An echocardiogram showed anteroseptal akinesia in the left ventricle with severely depressed LV function (EF=28%). An angiogram showed total occlusion in the proximal LAD with collaterals from the RCA and LCX.

End of Module VII b Reading 12-Lead ECGs Proceed to Module VII b Practice Quiz on WebCT

Module 7b

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Module 7b