12 Lead EKG. The Basics

Transcription

1 12 Lead EKG The Basics

2 Objectives Demonstrate proper 12 EKG lead placement Determine electrical axis Identify ST and T wave changes as they relate to myocardial ischemia Describe possible complications related to infarct location Treatment options based on infarct location

3 Limb leads RA- white right arm LA- black left arm RL- green right leg LL- red left leg

4 Precordial Leads V1-4 th IC space, right of sternum V2-4 th IC space, left of sternum V3- Between V4 and V2 V4-5 th IC space midclavicular V5-5 th IC space anterior axillary V6-5 th IC space, mid axillary

5 12 lead Assess rate and rhythm 2. Determine electrical axis 3. Identify conduction problems (BBB) 4. Identify ischemia, infarct signs Use these 4 steps as a fast and easy approach to every 12 lead interpretation

6 But first we all have to speak the same language Q wave is the first negative deflection after the P wave R wave is the first positive deflection after the P wave S wave is any negative deflection after the R wave

7 The J Point Where the QRS complex ends and the ST segment begins

8 Normal Conduction

9 Determining Axis Axis is the direction of the impulses in the heart Helps to identify which patients are at higher risk for complications Used to diagnose hemiblocks

10 Hemiblock Defined as a block in one of the hemifascicles of the left bundle branch In the presence of an acute MI a hemiblock puts the patient at a 4x greater risk of mortality

11 Axis Chart Look at leads I, II, and III Determine the QRS deflection (up or down) Compare it to the chart above

12 Bundle Branch Blocks The Bundle branch system is designed to spread the electrical impulses across the right and left ventricles equally so that they contract together. In a BBB the ventricles do not contract in sync because it took longer for the impulse to travel down the blocked side to stimulate that ventricle. Good contractility = Good cardiac output

13 Determining BBB Turn signal Theory QRS must be >.12 seconds Turn 12 lead page so that the top is to the right Look at V1 ONLY Which way is the QRS complex pointing? In this case it is to the right so this is a right BBB

14 Lets Try That Again Turn the page Look at V1 The QRS is pointing to the left Left BBB

15 This One s a Little Tougher Turn the page Look at V1 Look at the complex from the bottom of the page The first waveform deflection from the baseline determines the BBB In this case the first deflection is to the right. This is a right BBB

16 Now just to make it even more confusing With a left BBB the ST segments will always appear elevated. Remember the ventricles are out of sync. so the RV repolarizes first. Repolarization is seen on the EKG as a T wave. So, if the RV is repolarizing while the LV is depolarizing there is never a time when there is no electrical activity going on. Therefore, there is no baseline to record an isoelectric ST segment. This makes it non-diagnostic for an MI.

17 Myocardial Blood Supply

18 Right Coronary Artery (RCA) 1. Inferior wall of LV 2. SA node in 50% of patients 3. AV node in 90% of patients 4. RV What Supplies What? Posterior Descending Artery 1. Branch of RCA 2. Posterior wall of LV 3. Posterior fascicle of LBB 4. Left bundle branch Left Anterior Descending (LAD) 1. Anterior wall of LV 2. RBB, LBB 3. both fascicles of the LBB 4. Supplies the septal artery Circumflex Artery 1. Lateral wall of LV 2. SA node in 50% of patients 3. AV node in 10% of patients

19 Ischemia Defined as a transient reduction in blood flow Inverted T waves in two or more related leads ST depression in two or more related leads

20 Injury Damaged tissue Reversible acute injury ST segment elevation>1mm in two or more related leads Measure ST from the J point to the baseline This tissue is dying but not dead yet Every second counts!!!!!

21 Infarction Necrosis Dead tissue Q waves present When seen with elevated ST segments it indicates an ongoing MI Dead tissue cannot be saved. This is what we are trying to prevent

22 Look for ECG changes Assessing a 12 Lead ST segment elevation, Large T wave, T wave inversion Write down the leads where the changes are Look at the chart Next-look for ST depression Could be reciprocal changes for Infarcts

23 Reciprocal Changes Phenomenon where ST depression is seen in areas opposite to the infarct area. Does not indicate ischemia May help to rule out other causes for the chestpain

24 ST elevation in II, III, AVF Reciprocal changes in I, AVL Inferior MI

25 ST elevation V2-4 Anterior MI

26 ST elevation V1-4 Anterior-Septal MI

27 ST elevation I, AVL, V2-5 Reciprocal changes II, III, AVF Anterior-Lateral MI

28 ST elevation in V1, V2, V3 Reciprocal changes in II, III, AVF Anterior-Septal MI

29 Copy Cats Certain conditions can imitate an MI Remember LBBB is nondiagnostic for MI Thoracic aortic dissection Classic tearing pain between the shoulder blades No reciprocal changes Anticoagulation could be fatal Pericarditis ST elevations in all leads Leaning forward makes the pain better No reciprocal changes

30 12 Lead Pearls of Wisdom Chest pain with exertion= 70% occlusion Chest pain at rest= 90% occlusion Chest pain that doesn t resolve with NTG= 100% occlusion EKG changes can help predict which area of the heart is causing the trouble and help prepare for complications

31 More Pearls Limitations 12 leads could miss up to 50% of MI s Requires training to read ECG is only one piece of the puzzle Some conditions resemble MI Drug toxicities Electrolyte abnormalities A normal 12 lead does not rule out an MI

32 Still More Pearls Benefits If it shows an MI, you can be 90% sure it is there Able to rapidly identify early MI Able to identify complications Can commit to a course of treatment with ECG and a good history and physical

33 Anterior MI Most lethal Involves LAD At risk for V-fib, V-tach Develop CHF suddenly Can extend into septal and lateral walls Treatment Prepare for ventricular arrythmia Nitrates Be careful with fluids Use Beta blockers with caution as CHF may develop suddenly

34 Inferior MI Most Common Involves RCA 50% have RV and posterior involvement SA and AV node involved Look for bradycardia, hypotension Heart block Nausea Treatment Use nitrates with caution Fluids may be needed to keep BP up Use caution with beta blockade as heart rate may drop dramatically

35 Lateral MI Less common alone Usually seen as an extension of anterior or inferior MI Circumflex artery Look for: V-fib, v-tach Bradycardias (SA node in 50% of patients) Treatment Nitrates unless inferior involvement Cautious with fluids Use caution with Beta blockers

36 Posterior MI Difficult to diagnose with 12 lead EKG Can be seen as ST depression in all leads except ST elevation in AVR Use a Right sided EKG PDA branches from RCA Usually extended from inferior MI Look for: Bradycardia Heart blocks Treatment Cautious with nitrates May need fluids to keep BP up Use caution with beta blockade as Heart rate may drop dramatically

37 Right Sided EKG Perform 12 lead EKG Remove V4, V5, V6 and place as follows: V4R 5 th IC space mid clavicular line V8 posterior 5 th intercostal space mid scapular line V9 posterior between V8 and spine Perform the 12 lead with the leads in the new position Consider in Inferior MI and nondiagnostic 12 leads Finds 30% more infarcts

38 Note the ST elevations and reciprocal changes are consistant with inferior MI What are the ST depressions in V1-4? Perform a right sided 12 lead

39 The only leads that were moved are V4R, V8 and V9 so those are the only ones that have changed. Those ST elevations indicate a right ventricular MI and posterior MI What started out as an inferior MI now we know is and inferior, posterior, and right ventricular MI

40 Helpful link rial-in-ecg