EKG Basics OVERVIEW OF EKG AND TELEMETRY Outline

EKG Basics OVERVIEW OF EKG AND TELEMETRY

Outline 1. Review of the conduction system 2. EKG waveforms and intervals 3. EKG leads 4. Determining heart rate 5. Determining QRS axis

The Normal Conduction System

What is an EKG? The electrocardiogram (EKG) is a representation of the electrical events of the cardiac cycle. Each event has a distinctive waveform, the study of which can lead to greater insight into a patient’s cardiac pathophysiology.

What types of pathology can we identify and study from EKGs? Arrhythmias Myocardial ischemia and infarction Pericarditis Chamber hypertrophy Electrolyte disturbances (i. e. hyperkalemia, hypokalemia) Drug toxicity (i. e. digoxin and drugs which prolong the QT interval)

Waveforms and Intervals

EKG Leads are electrodes which measure the difference in electrical potential between either: 1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)

EKG Leads The standard EKG has 12 leads: 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads The axis of a particular lead represents the viewpoint from which it looks at the heart.

Standard Limb Leads

Standard Limb Leads

Augmented Limb Leads

All Limb Leads

Precordial Leads Adapted from: www. numed. co. uk/electrodepl. html

Precordial Leads

Summary of Leads Bipolar Limb Leads Precordial Leads I, III - (standard limb leads) Unipolar a. VR, a. VL, a. VF (augmented limb leads) V 1 -V 6

Arrangement of Leads on the EKG

Anatomic Groups (Septum)

Anatomic Groups (Anterior Wall)

Anatomic Groups (Lateral Wall)

Anatomic Groups (Inferior Wall)

Anatomic Groups (Summary)

Determining the Heart Rate Rule of 300 10 Second Rule

Rule of 300 Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the rate Although fast, this method only works for regular rhythms.

What is the heart rate? www. uptodate. com (300 / 6) = 50 bpm

What is the heart rate? www. uptodate. com (300 / ~ 4) = ~ 75 bpm

What is the heart rate? (300 / 1. 5) = 200 bpm

The Rule of 300 It may be easiest to memorize the following table: # of big boxes 1 Rate 2 150 3 100 4 75 5 60 6 50 300

10 Second Rule As most EKGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the EKG and multiply by 6 to get the number of beats per 60 seconds. This method works well for irregular rhythms.

What is the heart rate? The Alan E. Lindsay ECG Learning Center ; http: //medstat. med. utah. edu/kw/ecg/ 33 x 6 = 198 bpm

The QRS Axis The QRS axis represents the net overall direction of the heart’s electrical activity. Abnormalities of axis can hint at: Ventricular enlargement Conduction blocks (i. e. hemiblocks)

The QRS Axis By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°. -30° to -90° is referred to as a left axis deviation (LAD) +90° to +180° is referred to as a right axis deviation (RAD)

Determining the Axis The Quadrant Approach The Equiphasic Approach

Determining the Axis Predominantly Positive Predominantly Negative Equiphasic

The Quadrant Approach 1. Examine the QRS complex in leads I and a. VF to determine if they are predominantly positive or predominantly negative. The combination should place the axis into one of the 4 quadrants below.

The Quadrant Approach 2. In the event that LAD is present, examine lead II to determine if this deviation is pathologic. If the QRS in II is predominantly positive, the LAD is non-pathologic (in other words, the axis is normal). If it is predominantly negative, it is pathologic.

Quadrant Approach: Example 1 The Alan E. Lindsay ECG Learning Center http: //medstat. med. utah. edu/kw/ecg/ Negative in I, positive in a. VF RAD

Quadrant Approach: Example 2 The Alan E. Lindsay ECG Learning Center http: //medstat. med. utah. edu/kw/ecg/ Positive in I, negative in a. VF Predominantly positive in II Normal Axis (non-pathologic LAD)

The Equiphasic Approach 1. Determine which lead contains the most equiphasic QRS complex. The fact that the QRS complex in this lead is equally positive and negative indicates that the net electrical vector (i. e. overall QRS axis) is perpendicular to the axis of this particular lead. 2. Examine the QRS complex in whichever lead lies 90° away from the lead identified in step 1. If the QRS complex in this second lead is predominantly positive, than the axis of this lead is approximately the same as the net QRS axis. If the QRS complex is predominantly negative, than the net QRS axis lies 180° from the axis of this lead.

Equiphasic Approach: Example 1 The Alan E. Lindsay ECG Learning Center ; http: //medstat. med. utah. edu/kw/ecg/ Equiphasic in a. VF Predominantly positive in I QRS axis ≈ 0°

Equiphasic Approach: Example 2 The Alan E. Lindsay ECG Learning Center ; http: //medstat. med. utah. edu/kw/ecg/ Equiphasic in II Predominantly negative in a. VL QRS axis ≈ +150°

EKG Review 1. View the slide show 2. Interpret the EKGs 3. Advance slides to review findings 4. Good luck!

Recall the approach 1. Take a deep breath 2. Analyze rate 3. Analyze rhythm 4. Look at axis 5. Look for injury/strain/ischemic patterns 6. Look for conduction defecits (RBBB, LBBB) 7. Hypertrophy, meds, toxic effects 8. Make your measurments (PR, QT/QTc, QRS)

Sample EKG #1. Determine rate, rhythm, diagnosis, axis

Interpretation EKG#1 Rate: approx 75/min Rhythm: Baseline sinus rhythm, P: QRS is 1: 1 Axis: Physiologic Injury: ST elevation is present in the anterior, septal, and literal leads. Massive ST segment elevation is present in V 2 -V 6, with moderate ST elevation that obscures visualization of the QRS complex in lead one. Changes are consistent with LCA occlusion. Other: R wave progression is difficult to determine secondary to the pathological ST-T changes. No evidence of chamber enlargement or hypertrophy.

Sample EKG#2

Interpretation EKG#2 The EKG reveals an atrial flutter at a rate of approx 100 per minute. The QRS complexes are narrow and reveal a physiological axis. There is evidence of a premature ventricular complex, readily identifiable in the lateral chest leads. No evidence of ischemia or infarction. No evidence of R or L bundle branch block. Atrial flutter is conducted at approx 3: 1. (3 flutter waves to one QRS).

Sample EKG#3

Interpretation EKG#3 The EKG reveals an irregularly irregular rhythm suggestive of atrial fibrillation. The rate is variable, with a controlled or slow ventricular response. The axis is physiologic. ST-T changes suggestive of ischemia/injury are present in leads II, III, and a. VF. ST elevation of >1 mm in limb leads is indicative of a possible inferior wall myocardial infarction. Reciprocal changes are seen in leads one and a. VL. Early R wave progression.

EKG #4

Interpretation of EKG #4: This EKG reveals a baseline sinus rhythm. Rate cannot be determined definitively. The QRS is wide; V 1 reveals an RSR’ pattern consistent with a right bundle branch block. The axis is physiologic but is not easy to determine because of ST elevation present in leads III and a. VF (inferior wall). Other abnormal T changes are seen (T wave inversion) in leads V 1 -V 4. ST segment depression is present in the lateral chest leads as well. No evidence of chamber enlargement. ST elevation in III and a. VF with reciprocal depression in I and a. VL may be consistent with an inferior wall MI (RCA lesion. )

EKG #5

Interpretation of EKG#5: Baseline sinus rhythm. Rate appears normal (60 -100) Axis is physiologic No evidence of block or conduction abnormality There is widespread ST segment elevation in all leads GLOBAL ST elevation is consistent with pericarditis

EKG #6

EKG #6 Interpretation: EKG #6 reveals a baseline sinus rhythm. Rate approximately 80 bpm Axis is physiologic Complexes in V 5 greater than 35 mm suggest LVH ST segment depression in leads V 4 -V 6 in the setting of LVH is suggestive of a, “strain pattern”. No evidence of bundle brnach block ST segment depression in inferior chest leads

EKG #7

EKG #7 Interpretation: Baseline sinus rhythm. Rate of approx 80/min Axis is physiologic No evidence of ventricular hypertrophy, but RAH is possible due to P wave in lead II >0. 5 mm. Possible RBBB because of RSR’ in V 1 and QRS >0. 10 Note pathologic Q waves in II, III, a. VF Pathologic Q waves are >0. 04 s or >1/3 the height of the R wave. Changes consistent with inferior wall myocardial infarction (old, possibly transmural). R wave progression preserved.

EKG #8

Interpretation of EKG #8: Baseline sinus rhythm, rate approx 80. Right axis deviation, as evidenced by a primarily negative complex in lead I. Possible RAH due to large lead II P wave Possible RVH due to R>S in V 1 Note pervasive strain pattern due to RVH evidenced in precordial leads. The presence of RAD plus the R>S in V 1 is suggestive of RVH.

Any drug toxicity? EKG#8

EKG Interpretation #8: Though the picture has poor resolution, it is clear that the lateral leads reveal a pattern of digoxin toxicity. Even though rate is impossible to determine, the “cored-out” and depressed ST segments in the lateral precordial leads suggest digoxin toxicity. Furthermore, the irregular R to R intervals hint at a baseline rhythm of atrial fibrillation. Many patients take digoxin for chronic atrial fibrillation. Moderate left axis deviation.

EKG #9

EKG #9: This rhythm strip reveals a profound bradycardia. There is no relationship between the atria (P waves) and QRS complexes. This is consistent with complete A-V dissociation, or third degree heart block. This rhythm frequently requires emergent pacing.

EKG #10

EKG #10 Interpretation: This EKG reveals a baseline sinus rhythm (p’s are difficult to discern. ) The rhythm is a sinus tachycardia at approximately 100 per minute. Massive ST segment elevation is present in leads II, III, and a. VF. Reciprocal changes (depression) in leads I and a. VL. Note that the precordial chest leads (v 4 R to V 6 R) are placed on the right side of the chest. ST segment in a “right-sided” EKG likely indicates an inferior wall MI that involves the RIGHT ventricle. Be careful when giving these patients NTG. Administration of nitrates, due to the alteration of venous preload, can precipitate hypotension. Treat these MI’s with fluid first. The axis is physiologic, no evidence of chamber enlargement. R wave progression is not of value in this EKG because of the right sided chest leads.

Final Rhythm Review

Rhythm interpretation: -The first strip reveals a prolonged PR interval, with 1: 1 conduction. This rhythm is a first degree A/V block. -The second strip is a 4: 1 (or 3: 1) atrial flutter. -The third rhythm strip reveals the typical atrial fibrillation. Note the fibrillatory baseline with irregular R to R intervals.

The QT/QTc Interval: Calculation and Significance Measurement: Parameter: Abnormalities: QTc: Lengthening: From the beginning of the Q wave to the end of the T wave Normal QT intervals range from 0. 360. 41. Hypercalcemia will shorten the QT interval and yield measurements from 0. 26 -0. 36 s. The QT interval varies with heart rate. The corrected QT interval is calculated by adjusting your measurement for the patient’s heart rate. The QT divided by the square root of the R to R interval typically gives a QTc around 0. 44 seconds. Diseases, drugs, and toxins can prolong the QT interval and precipitate attacks of lethal ventricular arrhythmias.

Long QT syndrome, “Romano-Ward” Syndrome EKG: The QTc, adjusted for rate, would almost certainly be greater than 0. 44 seconds. You can see in this example that the QTc is approximately 0. 5 -0. 6 seconds (almost 3 large boxes!)

Rate Cheat Sheet Besides calculating the number of R waves in a 3 or 6 second strip and multiplying by 20 or 10 seconds, simply divide the number of small (0. 04 s) units between consecutive R waves into 1500. -The heart rate can also be calculated from the R to R interval. Simply divide the number of large boxes (0. 2 s) between consecutive R waves into 300. -15 large boxes is a three second strip! -30 large boxes represents a six second strip! -For irregularly irregular rhythms, try to calculate rate with a decent time interval, preferably greater than a 3 second strip.

Potassium summary:

Digitalis effect summary: In addition to a wide variety of atrial conduction defects, ventricular ectopy, and heart blocks, early digitalis toxicity manifests itself as: a shortening of the QT interval in addition to scooped-out appearing ST segments.

Precise axis calculation, anyone? Remember that it is simply a method of addition. I+III=II. The mean QRS vector will also point 90 degrees away from the most isoelectric lead. Leads with large amplitude R waves will shift the mean QRS vector in their general direction. Remember about dropping those stubborn perpendiculars?

Chamber enlargement review: Name that hypertrophy? a) RVH b) LVH c) RAH d) LAH

The EKG findings are consistent with: RVH Criteria for right ventricular hypertrophy include: -Tall R wave in lead V 1 (R>S) -q. R pattern in V 1 -Right axis deviation -T wave inversion in right to mid precordial leads possible -Commonly due to ASD! -The pattern of T wave inversion is called, “strain”and is consistent with repolarization problems in hypertrophied muscle.

For the following strips identify the QRS, QT, Heart Rate, PR, ST, intervals, and whether or not the rhythm is normal or abnormal. Try your best to identify the rhythm. A. Normal Sinus Rhythm B. Atrial Fibrillation C. Normal Sinus Rhythm with Heart Block