ECG

Axis

What is the four quadrant method, based on I, and AVF and how are they used to determine the axis?

The Four Quadrant Method is a way of determining the electrical axis of the heart using the standard 12-lead ECG. Specifically, it involves analyzing the QRS complex in the I (Lead I) and AVF (Lead aVF) leads, which are typically used to determine the overall direction of the heart's electrical activity. In the ECG, look at the QRS complex in both Lead I and Lead aVF. Determine whether the QRS complex in each lead is positive (upright) or negative (downward).

Normal Axis: Lead I = Positive, Lead aVF = Positive.

Left Axis Deviation: Lead I = Negative, Lead aVF = Positive.

Right Axis Deviation: Lead I = Negative, Lead aVF = Negative.

Extreme Right Axis Deviation: Lead I = Positive, Lead aVF = Negative.

What does a wide QRS-T angle mean?

If the QRS and T wave are both upright In I, II, and AVF, they are in normal range, otherwise, you should determine both vectors to determine the QRS-T angle to see that it is Normal (50 to 60 degrees of each other). A wide QRS-T angle suggests that the electrical forces responsible for depolarization and repolarization are not aligned. In other words, there may be a mismatch between the QRS axis and the T wave axis.

What abnormalities can produce a wide QRS-T angle?

BBB
Hypertrophy
1. How do you determine a normal P and T vector?

Axis for the P and T wave can be determined the same way as the QRS wave

P Axis

The normal P wave axis is between 0 to 70 degrees If the P wave is upright in leads I, II, and AVF, in normal range

T Axis

The normal T wave axis should be within 50 to 60 degrees of the QRS axis.

How do you determine if there is an anterior or posterior tilt with the heart’s vector?

V1, V2 both QRS’s Negative- posterior tilt

V1, V2 both QRS’s Positive- anterior tilt

V1, V2 one QRS positive and one negative- no anterior or posterior tilt

Based on the direction of the vector, what frontal and horizontal planes are included?

Frontal Plane (Vertical Plane):

Analyzes the left-to-right and upward-to-downward direction of the heart's electrical vector.
The axis is measured in degrees, with typical values ranging from 0° to +180°.
Can use the quadrant method and use lead I, and aVf, or use the hexaxial method and find a more specific axis using all the frontal leads (I, II, III, aVf, aVr, aVl)
QRS axis in the frontal plane can be:
- Normal axis: 0° to +90° (downward and to the left).
- Left Axis Deviation (LAD): -30° to -90°.
- Right Axis Deviation (RAD): +90° to +180°.
- Extreme axis (or Northwest axis): -90° to -180°.

Horizontal Plane (Transverse Plane):

Analyzes the anterior-to-posterior direction of the heart's electrical vector.
This plane is often studied with the precordial leads (V1-V6), which represent the electrical activity from the front to the back of the chest.
The axis can be tilted:
- Anterior tilt: electrical vector directed more anteriorly
- Posterior tilt: electrical vector directed more posteriorly
Often use leads V1 and V2 to determine the horizontal axis of the hearts vector.

If a lead is biphasic, what direction is the vector traveling?

When a lead is biphasic, the electrical vector is traveling roughly perpendicular to the line connecting the positive and negative electrodes, meaning it is moving neither directly towards nor directly away from the recording electrode, resulting in a waveform with both positive and negative deflections.

Hypertrophy

What abnormalities are responsible for causing atrial enlargement and ventricular hypertrophy?

- HTN (Pressure Overload)

- Heart Valve Disease (Pressure or Volume Overload)

- CAD

- Cardiomyopathy (muscle disease)

- Congenital defects

Hypertrophy: is reflective of the ventricles

Enlargement: is reflective of the atria

Left Atrial Enlargement

Mitral valve disease
Chronic HTN

Right Atrial Enlargement

Severe lung disease
tricuspid valve disease

Left Ventricular Hypertrophy

HTN
Valvular Diseases (aortic stenosis)

Right Ventricular Hypertrophy

Pulmonary disease
Congenital Heart Disease

What are the ECG criteria for the different ways in which to determine hypertrophy and enlargement?

Left Atrial Enlargement

Duration of the P wave is increased in II
Terminal portion of the P wave > 1 mm below baseline in V1
Terminal portion of the P wave 1 block (.04 sec) wide in V1

Right Atrial Enlargement

P wave > 2.5mm amplitude in at least one of the Inferior leads ( II, III, AVF)
No change in the duration of the P wave

Left Ventricular Hypertrophy

The R-wave amplitude in lead V5 or V6 plus the S wave amplitude in lead V1 or V2 exceeds 35 mm.
The R-wave amplitude in lead V5 exceeds 26 mm.
S wave in V1 and R wave in V6 exceeds 35mm
The R-wave amplitude in lead aVL exceeds 11 mm.

Right Ventricular Hypertrophy

Right Axis Deviation (RAD)
V1; R wave > S wave
V6; S wave > R wave

Ischemia/Infarction

What ECG abnormalities are associated with a STEMI?

This represents a total occluded coronary artery, representing a true emergency because the heart is being starved of blood. ECG- ST elevation
T wave peaking, hyer-actue T waves almost the height of the R waves (myocardial ischemia). This is followed by Symmetrical T wave inversion after a couple hours
Significant Q waves are >.04 sec wide and > 25% the height Of the R wave

What ECG abnormalities are associated with a NSTEMI?

This is caused by a reduced blood flow but not totally blocked which can lead to unstable angina or NSTEMI. ECG- ST segments most likely depressed or normal
T wave inversion

How does ischemia appear on the ECG when comparing resting vs exerting oneself?

More significant ST depression ≥ 1 mm ST depression (horizontal or downsloping) .08 sec past the J point.

What ECG changes take place from an acute infarct to an old infarct (changes over time)?

Normal morphology: normal
Hyperacute T waves (wide and tall): Minutes
ST elevation: Hours
Significant Q waves and T-wave inversion: Hours to days
ST elevation improves: Days to weeks
Significant Q waves persist, T-waves normalize: Weeks to months

What does ischemia represent physiologically?

Ischemia represents a pathophysiological condition where there is an insufficient supply of oxygen-rich blood to a tissue or organ, typically due to an obstruction or narrowing of the blood vessels that supply it. In the context of the heart, ischemia specifically refers to insufficient blood flow to the myocardial tissue (heart muscle), which leads to oxygen deprivation. This imbalance between oxygen demand and supply can have significant consequences for the heart's electrical, mechanical, and metabolic function.

What ECG leads reflect certain walls of the myocardium for ischemia and infarction?

Inferior Myocardial Infarction

Involves occlusion of the RCA
Significant Q waves in leads II, III, aVF
Seeing Sig. Q waves in two of the three leads is acceptable to say Inferior MI

Lateral Myocardial Infarction

Involves occlusion of the left circumflex
ST segment elevation observed in I, aVL, V5,V6
Changes in two of the four leads is acceptable to say Lateral MI
Reciprocal changes observed in inferior leads

Anterior Myocardial Infarction

Involves occlusion of the LAD
Best identified in leads V1 to V4
Poor R wave Progression (R wave in V3 < 3mV)
Large influence on the LV

Posterior Myocardial Infarction

Typically Involves occlusion of the RCA
Rarely occurs in isolation, usually combined with Inferior wall and possibly lateral wall
Look for reciprocal changes in the anterior leads (V1, V2, V3) because there is no electrodes directly on the posterior wall (R=Q, ST Depression=ST Elevation)
R wave > S wave in VI suggestive of posterior MI
Additional leads- V8, V9, V4 (15 LeadECG)

What are the different morphologies of ST depression and which one’s are indicative of ischemia?

horizontal and downsloping ST depression are more concerning for ischemia, especially if they occur during stress testing or exertion, while upsloping ST depression is usually not associated with ischemia and may reflect other causes

How does one properly measure the ST segment, if it is elevated or depressed?

The baseline is the isoelectric line, which represents the period of the ECG where there is no electrical activity. This is usually the segment of the ECG that is flat before the P-wave or between the T-wave and P-wave.

In the case of normal sinus rhythm, the baseline is typically the TP segment (between the end of the T-wave and the beginning of the P-wave).

ST Elevation:

ST-segment elevation is defined as an upward deflection of the ST segment from the baseline.
- Elevation is typically considered significant if it is greater than or equal to 1 mm (0.1 mV) in at least two contiguous leads.
- Contiguous leads mean leads that look at the same region of the heart (e.g., leads I, aVL, V5, and V6 are all considered lateral leads).

ST Depression:

ST-segment depression is defined as a downward deflection of the ST segment from the baseline.
- Depression is typically considered significant if it is greater than or equal to 1 mm (0.1 mV) below the baseline.

What is a reciprocal ECG change to an acute MI?

In leads that are distant from the MI area, will have an increase in electrical forces moving toward them (larger R waves) along with ST depression In some leads.

Exam will be a combination of multiple choice questions and ECGs (similar to Test#2). You will not be asked any questions pertaining to rate and rhythm, we will save that for the final!

Practical Review

Leads

Anatomical Electrode Placement

Limb Electrodes:

Right Arm (RA): place under right clavicle in the subclavicular fossa at the midclavicular line
Left Arm (LA): place under left clavicle in the subclavicular fossa at the midclavicular line
Right Leg (RL): Last palpable rib on the right side in line with the mid clavicular
Left Leg (LL): Last palpable rib on the left side in line with the mid clavicular

Precordial Electrodes:

V1: 4th intercostal space, right sternal border.
V2: 4th intercostal space, left sternal border.
V3: Midway between V2 and V4.
V4: 5th intercostal space, midclavicular line.
V5: Anterior axillary line, on the same horizontal level as V4
V6: Mid-axillary line on the same horizontal level as V4 and V5

All Dysrhythmia Criteria

Normal Sinus Rhythm:

Rhythm: Regular

Rate: 60-100

P wave: p before each QRS, upright and positive

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

Atrial Dysrhythmias

Sinus Bradycardia:

Rhythm: Regular

Rate: <60

P wave: p before each QRS, upright and positive

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

Sinus Tachycardia:

Rhythm: Regular

Rate: >100

P wave: p before each QRS, upright and positive

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

Sinus Dysrhythmia:

Rhythm: Irregular

Rate: NA

P wave: p before each QRS, upright and positive

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

SA Block:

Rhythm: Irregular w/ pauses

Rate: NA

P wave: p before each QRS, upright and positive

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

-Pauses, P waves march through

Sinus Arrest:

Rhythm: Irregular w/ periods of asystole

Rate: NA

P wave: p before each QRS, upright and positive

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

-Pauses, P waves don’t march through

-Three or more beats missing

- SA node not healthy

Sinus Pause:

Rhythm: Irregular w/ periods of asystole

Rate: NA

P wave: p before each QRS, upright and positive

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

-Pauses, P waves don’t march through

- < Three beats missing

- SA node not healthy

Sick Sinus Syndrome:

Rhythm: Irregular

Rate: NA

P wave: p before each QRS, upright and positive

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

-Form of sinus arrest

-SA node not healthy

-Brady- tachy rhythm

Premature Atrial Contractions (PAC):

Rhythm: Irregular

Rate: NA

P wave: P shaped different

P-R Interval: <> 0.12-0.20

QRS: < 0.12 after each P wave

-observe premature early beat w/ different P wave shape

-typically followed by a pause

AV Node Reentry tachy or SVT:

Rhythm: normally regular

Rate: 150-250 bpm

P wave: may or may not be seen, could be inverted

P-R Interval: 0.12-0.20

QRS: < 0.12 after each P wave

-Fast rate originating in the atria and leading to a reentry phenomenon

- If inverted P = most likely AV node re-entry

Atrial Flutter:

Rhythm: NA

Rate: 250-300 bpm

P wave: multiple P waves, saw tooth pattern

P-R Interval: NA

QRS: < 0.12 after each P wave

-Multiple P waves for each QRS

Atrial Fibrillation:

Rhythm: irregular

Rate: NA

P wave: difficult to discern

P-R Interval: NA

QRS: < 0.12 after each P wave

-R-R irregular

Multifocal Atrial Tachycardia:

Rhythm: irregular

Rate: 100-200

P wave: changing

P-R Interval: varies

QRS: < 0.12 after each P wave

-firing from multiple area in the atrium at a fast rate

Wandering Atrial Pacemaker:

Rhythm: irregular

Rate:< 100

P wave: changing

P-R Interval: varies

QRS: < 0.12 after each P wave

-firing from multiple area in the atrium

Junctional Dysrhythmias

Junctional Escape Beat:

Rhythm: irregular

Rate: NA

P wave: P wave inverted before or after QRS, or no P

P-R Interval: <0.12 if present

QRS: < 0.12 after each P wave

-typically follows a pause, giving AV node time to fire

Junctional Escape Rhythm:

Rhythm: regular

Rate: 40-60

P wave: P wave inverted before or after QRS, or no P

P-R Interval: <0.12 if present

QRS: < 0.12 after each P wave

Ventricular Dysrhythmias

PVCs Unifocal or Multifocal:

Rhythm: NA

Rate: NA

P wave: Not present

P-R Interval: NA

QRS: > 0.12 sec

-T wave opposite direction of QRS

-Unifocal = same

-multifocal = different

Ventricular Couplet:

Rhythm: NA

Rate: NA

P wave: Not present

P-R Interval: NA

QRS: > 0.12 sec

-Two Consecutive ventricular beats

Ventricular Tachycardia (VT):

Rhythm: regular

Rate: 120-200

P wave: Not present

P-R Interval: NA

QRS: > 0.12 sec

-Three or more consecutive ventricular beats

Accelerated Idioventricular Rhythm (AIVR):

Rhythm: regular

Rate: 40-100

P wave: Not present

P-R Interval: NA

QRS: > 0.12 sec

-Three or more consecutive ventricular beats

-T wave opposite direction of QRS

Idioventricular Rhythm (IVR):

Rhythm: regular

Rate: <40

P wave: Not present

P-R Interval: NA

QRS: > 0.12 sec

-Three or more consecutive ventricular beats

-T wave opposite direction of QRS

Ventricular Fibrillation (VFib):

Rhythm: irregular

Rate: Can’t determine

P wave: Not present

P-R Interval: NA

QRS: can’t determine

-Chaotic, can’t clearly define waves

Asystole:

Rhythm: Can’t determine

Rate: Can’t determine

P wave: Not present

P-R Interval: NA

QRS: NA

-No electrical activity

Conduction Abnormalities

1st Degree AV Block:

Rhythm: Regular

Rate: NA

P wave: Present and up right

P-R Interval: > 0.20 sec

QRS: < 0.12 after each P wave

-Delay in AV node causing P-R to be longer than normal

2nd Degree AV Block, Type 1:

Rhythm: Irregular

Rate: NA

P wave: Present and regular

P-R Interval: progressively longer

QRS: < 0.12 after each P wave

-P-R gets longer to the point where there is a P without a QRS

-Delay in AV node

2nd Degree AV Block, Type 2:

Rhythm: Irregular

Rate: NA

P wave: Present and regular

P-R Interval: normal 0.12- .20

QRS: < 0.12 after each P wave

-P-R is not changing

-Occasional P waves with no GRS

3rd Degree AV Block:

Rhythm: regular on its own

Rate: A and V rate different

P wave: Present and regular

P-R Interval: constantly changing

QRS: normal or wide >0.12

-No association between P and QRS

RBBB:

Rhythm: regular

Rate: NA

P wave: Present and regular

P-R Interval: normal 0.12- .20

QRS: wide >0.12

-V1, V2 have RsR’

-V5, V6 large S waves

LBBB:

Rhythm: regular

Rate: NA

P wave: Present and regular

P-R Interval: normal 0.12- .20

QRS: wide >0.12

-V5, V6 have notched or slurred R waves

-V1, V2 large S waves

WPW Syndrome:

Rhythm: regular

Rate: NA

P wave: Present and regular

P-R Interval: < 0.12

QRS: wide >0.12

-delta waves

-Accessory Pathway is allowing impulse into the ventricles from the atrium

LGL Syndrome:

Rhythm: regular

Rate: NA

P wave: Present and regular

P-R Interval: < 0.12

QRS: < 0.12 after each P wave

-Short P-R

-Accessory Pathway that bypasses the AV node and attaches to the bundle of his.

Pacemakers

Atrial Pacemaker:

Rhythm: regular when firing

Rate: NA

P wave: present, may look different

P-R Interval: may change

QRS: < 0.12 after each P wave

-spike right before each p wave

Ventricular Pacemaker:

Rhythm: regular when firing

Rate: NA

P wave: present or absent

P-R Interval: NA

QRS: > 0.12

-spike right before each QRS

A/V Pacemaker:

Rhythm: regular when firing

Rate: NA

P wave: present, may look different

P-R Interval: NA

QRS: > 0.12

-spike right before each QRS and P wave

Enlargement and Hypertrophy Criteria

Left Atrial Enlargement

Duration of the P wave is increased in II
Terminal portion of the P wave > 1 mm below baseline in V1
Terminal portion of the P wave 1 block (.04 sec) wide in V1

Right Atrial Enlargement

P wave > 2.5mm amplitude in at least one of the Inferior leads ( II, III, AVF)
No change in the duration of the P wave

Left Ventricular Hypertrophy

The R-wave amplitude in lead V5 or V6 plus the S wave amplitude in lead V1 or V2 exceeds 35 mm.
The R-wave amplitude in lead V5 exceeds 26 mm.
S wave in V1 and R wave in V6 exceeds 35mm
The R-wave amplitude in lead aVL exceeds 11 mm.

Right Ventricular Hypertrophy

Right Axis Deviation (RAD)
V1; R wave > S wave
V6; S wave > R wave

Secondary Repolarization Abnormality Caused by Ventricular Hypertrophy

Downsloping ST depression and T wave inversion