12-Lead Electrocardiographya comprehensive course

Adam Thompson, EMT-P, A.S.

Morphologi

es(The

“QRS”)

QRS Complex

The morphology of the QRS complex will assist us in identifying BBBs, V-tach, LVH, RVH, and infarction.

QRS Complex

• Height & Morphology will vary, depending on the lead.

• Normal Width– > 0.10 seconds– < 0.12 seconds

Bundle Branches

Bundle Branch Blocks

• Right Bundle Branch Block (RBBB)– The single right fascicle is blocked.

• Left Bundle Branch Block (LBBB)– Both left fascicles are blocked.

• Non-Specific Intraventricular conduction delay (IVCD)– BBB that doesn’t meet RBBB or LBBB criteria.

Bundle Branch Blocks

• May mimic an MI• The side that is blocked conducts last and

takes longer.

Bundle Branch Blocks

• Normal conduction without a block. 1

32

2

3

4

Mean vector

Cardiac vector

Right Bundle Branch Block

+

+

+ A B A

B

Mean vector moves towards positive electrode = positive QRSMean vector moves away from positive electrode = negative QRSMean vector is perpendicular to positive electrode = equiphasic QRS

Bundle Branch Blocks

• With a RBBB, the right fascicle is blocked, so the left ventricle is conducted first and then the impulse returns to the right.

1

2

3

Bundle Branch Blocks

• With a LBBB, the right ventricle is conducted first, and the impulse travels back to the left.

1

2

3

Bundle Branch Blocks

V1

Bundle Branch Blocks

J-Points

The J-point is the exact point where the QRS ends

V1

Bundle Branch Blocks

V1

Bundle Branch Blocks

V1

Bundle Branch Blocks

V1

Bundle Branch Blocks

= RBBB

= LBBB

V1

V1

Bundle Branch Blocks

V1

RBBB

LBBB

Right Bundle Branch Block

• RBBB morphologies

V1

Right Bundle Branch Block

Left Bundle Branch Block

V1

Left Bundle Branch Block

Intraventricular Conduction Delay

• A Non-specific IVCD is less common than a RBBB or LBBB

• They are wide, atrial rhythms that usually look like a left or right BBB in V1, but do not match the criteria in I & V6.

Ventricular Enlargement

• Left Ventricular Hypertrophy (LVH)– The left ventricle is enlarged– Probably due to left-sided heart failure

• Right Ventricular Hypertrophy (RVH)– The right ventricle is enlarged– Probably due to right sided heart failure– May be due to pulmonary disease

Ventricular Enlargement

• Left Ventricular Hypertrophy (LVH)– May cause left axis deviation– May cause a left ventricular strain pattern

• Often mimics an anterior MI

• Right Ventricular Hypertrophy (RVH)– May cause right axis deviation– May cause a right ventrcular strain pattern

• May mimic a inferior or posterior wall MI

LVH

RV LV Hypertrophy

Normal LVH

LVH

LVH Criteria– Large QRS complexes

• Deepest S-wave in V1 or V2• Tallest R-wave in V5 or V6

– Add them together» If the result is > 25mm = LVH

LVH

V1 or V2

S R

V5 or V6

+

LVH

Lets take a look at an example

LVH

Lets take a look at an example

LVH

Lets take a look at an example

LVH

Lets take a look at an example

14mm

LVH

Lets take a look at an example

14mm

LVH

14 + 15 = 29mm

14mm 15mm

LVH

• Since our total was 29mm, and a total of > 25mm meets LVH criteria, we can assume that this ECG is that of a patient with LVH.

*LVH may look a lot like a narrow LBBB.

LVH

• A wave that is too tall or deep may be cut off by the monitor

• This is a indicator of hypertrophy

LVH

• A wave that is too tall or deep may be cut off by the monitor

• This is a indicator of hypertrophy

LVH

Additional LVH Criteria

Any precordial lead

> 45mm

aVL > 11mm

Lead I > 12mm

aVF > 20mm

Ventricular Leads

Right Ventricular Left Ventricular

RVH

• Right Ventricular Hypertrophy– Criteria = R:S ration > 1 in V1/V2

• This means that the R-wave is bigger than the S-wave in V1 or V2.

• The QRS complex should be narrow• P-Pulmonale may be present.• Right axis deviation is common.

RVH

V1 or V2

R

S

V1/V2: R > S = RVH• QRS < 120ms (0.12 sec)

= 9mm

= 6mm

RVH

RVH

Let’s take a look…

RVH

Let’s take a look…

PathologiesFrontal Plane Axis Precordial Axis

ERAD-90 to 180

Right Axis Deviation90 to 180

Pathological Left Axis Deviation

-30 to -90

Early TransitionCounterclockwise

Rotation

Late TransitionClockwise Rotation

• Ventricular Rhythm• Paced Rhythm• Dextrocardia• Electrolyte derangement

• May be normal• LPFB• Pulmonary disease• RVH• RBBB• WPW• Dextrocardia•Venrticular Rhythm

• Pregnancy• LAFB• WPW• Pulmonary disease• LBBB• Hyperkalemia• Q-waves, MI

• Posterior wall infarction• RVH• RBBB• WPW

• Sometimes Normal, especially in women• Anterior MI• LVH• LAFB• LBBB• Lung Disease

QRS Complex

Low Voltage– Chronic Cor Pulmonale

• Progressive lung disease, leading to right-sided heart failure.– Pericardial Effusion

• Fluid in the pericardial sac.– Excessive Obesity

END

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