TS3 Electrocardiogram III & IV

Required Readings:   Aehlert, Chap. 9

Goal:     Be able to analyze and interpret single and 12 lead electrocardiograms.

Objectives:

• Be able to measure the P-R interval, QRS complex, Axis, rate and rhythm given a 12 lead EKG

Anonymous AEHLERT 199

The hexaxial reference system represents all of the frontal plan (limb) leads with the heart in the center and is the means used to express the location of the frontal plane axis.  This system forms a 360-degree circle surrounding the heart.  The positive end of lead I is designated at 0 degrees.  The six frontal plane leads divide the circle into segments, each representing 30 degrees.  All degrees in the upper hemisphere are labeled as negative degrees, and all degrees in the lower hemisphere are labeled as positive degrees.  The mean QRS vector (normal electrical axis) lies between 0 and 90-degrees

-Current flow to the right of normal (+90-+180) is right axis deviation

-Current flow to the left of normal (-1 to -90) is left axis deviation

-Current flow in the direction opposite of normal (-91 to-179) is called indeterminate   (“no man’s land”), northwest, or extreme right axis deviation.

Two lead method of axis determination:

•        Given a 12 lead EKG, be able to identify changes associated with injury, ischemia, infarction and inflammation using the P-R interval or QRS complex as applicable.

Jenn, Dubin p269

1.                  Injury:  See below obj 4.

2.                  Ischemia:  See below obj 4

3.                  Infarction:See below obj 4

4.                  Inflammation:  With pericarditis , the ST segment is elevated and usually flat or concave.  The entire T wave may be elevated off the baseline.  Pericarditis can elevate the ST segment.  It usually produces an elevated ST segment that is flat or slightly concave (middle sags downward).  This resolves with time.

Anonymous AEHLERT 200-204

Injury:

Acute phase:  ST segment elevation > than 1 m above baseline in two or more limb leads and > 2mm in two or more precordial leads

Reversible

Ischemia

            Evolving phase

            ST segment depression 0.5 mm or more below baseline

            And/or T wave inversion

Reversible

Infarction

            Loss of R waves (precordial leads)

            Q waves:          Duration of 0.04 seconds or greater

                                    ¼ height of the R waves

                                    Appear in several leads at once

                                    Permanent damage.

• Know the voltage criteria for ventricular hypertrophy.

Jenn, Dubin pg 251-55

1.      With Right Ventricular Hypertrophy there is a lg R-wave in V₁.  With RVH, the wall of the right ventricle is very tick, so there is much more (positive) depolarization (and more vectors) toward the positive V₁ electrode.  We would therefore expect the QRS in lead V₁ to be more positive (taller) than usual.  The S wave in lead V₁ is smaller than the R wave in RVH.

2.      With Left Ventricular Hypertrophy there is a very lg S in V₁ and a lg R in V₅.  Depth (in mm) of S in V₁  plus the height of R in V₅…if greater than 35m, there is LVH.

Anonymous AEHLERT 221

Ventricular muscle hypertrophies when it sustains a persistent pressure overload. Hypertrophy increases the QRS amplitude and is often associated with ST-segment depression and asymmetric T-wave inversion.

Ventricular enlargement: assess leads V1-V6

1. Right Ventricular Hypertrophy:

Tall R waves in V1, V2 (may also be seen in RBBB, posterior MI, WPW)

Deep S waves V5, V6

b.   Left Ventricular Hypertrophy
                  Tall R waves in V5, V6

                  Deep S waves in V1, V2

Amplitude of S waves in V1 in mm + amplitude of R wave in V5 or V6 in mm is greater than 35 mm

• Given a 12 lead EKG, be able to identify the location of a myocardial infarction.

Jenn, Dubin pg 263-67, 272

The myocardial infarction triad is ischemia, injury, and necrosis, but any of the three may occur alone.  The myocardial infarction triad is the basis for recognizing and diagnosing an MI.

1.                  The characteristic sign of ischemia is the inverted T wave.  It may vary from a slightly inverted to a deeply inverted T wave.  The typical ischemia T wave is symmetrically inverted.

2.                  Injury indicates the acuteness of an infarct.  Elevation of the ST segment denotes injury sometimes called the “current of injury.”  The ST segment may be elevated only slightly or as much as 10mm or more above the baseline.

3.                  The Q wave indicates necrosis and makes the diagnosis of infarction.  The diagnosis of myocardial infarction is usually based on the presence of significant Q waves produced by an area of necrosis in the wall of the left ventricle.

Anonymous

Evaluate each area for:

            Injury: ST elevation

            Ischemia: ST depression, T inversion

            Infarction: Q waves, loss of R waves

Inferior: Lead II, Lead III, AVF

Anterior: V3, V4

Septal: V1, V2

Lateral: V5, V6, Lead I, AVL

Posterior: V1, V2 (reciprocal)

RV: V4R, V5R, V6R  

2. Given a 12 lead EKG be able to identify the following electrolyte abnormalities: hypokalemia, Hyperkalemia, Hypocalcemia, and Hypercalcemia. MEDEX37

Zen Seeker 

hyperkalemia
K= 5.5: T-waves became tall and peaked
K= 6.5: QRS changes start
K>7.0: P-waves decreased pwave amplitude
K>8.0 P-wave becomes invisible
K> 12: Vfib or asystole

narrow and peak T waves (tenting)
AV conduction disturbance (PR prolongation or disappeared P wave) and wide QRS
cardiac arrest with a slow sinusoidal wave ('sine-wave pattern')
asystole
renal failure 환자에서는 hyperkalemia 와 hypocalcemia 가 같이 있는 경우가 많으므로 사막에 텐트를 친 것과 같은 "tent on the desert' 패턴이 보이게 됩니다.

hypokalemia
prominent U wave, prolonged ventricular repolarization (QT interval)
QRS Complex: Begins to widen at a serum potassium level of about 3.0 mEq/L.

ST Segments: May become depressed by 1 mm or more.

T Waves: Begin to flatten at a serum potassium level of about 3.0 mEq/L and continue to become smaller as the U waves increase in size. The T waves may either merge with the U waves or become inverted.

U Waves: Begin to increase in size, becoming as tall as the T waves at a serum potassium level of about 3.0 mEq/L and, at about 2 mEq/L, becoming taller than the T waves. The U waves reach "giant" size and fuse with the T waves at 1 mEq/L.

QT Intervals: May appear to be prolonged when the U waves become prominent and fuse with the T waves but actually remain normal.

Associated Arrythmias: Ventricular arrhythmias, including the torsade de pointes form of ventricular tachycardia. May occur in hypokalemia in the presence of digitalis.

K< 2.7: U wave large U-wave or TU complex
Depress ion of ST segment >0.5mm
U-wave amplitude > 1.0 mm
U-wave> Twave
 

hypercalcemia
shortened QT interval
 

Foreshortened ST segment
QT inverval shortened (Qtc of less than 270ms is 90% of the time related to hypercalcemia
 

hypocalcemia
lengthened QT interval

Long ST

3. Be able to identify the pacemaker spike on an EKG MEDEX37

Zen Seeker