Electrocardiography (EKG) Lab

What is this?

EKG Graph

P Wave

Define P Wave:

Depolarization of Atria

P-R Segment

Define P-R Segment:

The time from the end of the P wave to beginning of QRS complex.

Normal Duration = 0.02-0.12 sec

QRS Complex

Define QRS Complex:

Depolarization of ventricles

S-T Segment

Define S-T Segment:

The time from the end of the S wave to the beginning of the T wave.

Normal Duration = 0.05-0.15 sec

T Wave

Define T Wave:

Repolarization of ventricles

T-P Segment

Define T-P Segment:

The time from the end of the T wave to the beginning of the P wave.

Normal Duration = 0.2-0.4 sec

R-R Interval

Define R-R Interval:

The time of one cardiac cycle.

Average resting value = 0.8 sec.

P Wave EKG Electrical + Mechanical Events:

Electrical: The depolarization wave is traveling from the SA node toward the Av node + through gap junctions to excite the contractile cells in both atria.

Mechanical: AV valves remain open and SL valves remain closed from the previous cycle. Blood is passively filling the ventricles. The atria start to contract.

P-R Segment EKG Electrical + Mechanical Events:

Electrical: No electrical events are occurring.

Mechanical: Atria Systole is occurring; Last 20% of blood pushed into ventricles

QRS Complex EKG Electrical + Mechanical Events:

Electrical: Ventricular Depolarization

Mechanical: Atrial Systole ends; Atrial diastole begins; Ventricular systole starts (Atrial Pressure > Ventricular Pressure); AV Valves close

S-T Segment EKG Electrical + Mechanical Events:

Electrical: No electrical events are occurring.

Mechanical: The ventricles continue to contract. When ventricular pressure exceeds arterial pressure, the SL valves open, and blood is ejected into the arteries.

T Wave EKG Electrical + Mechanical Events:

Electrical: Ventricular Repolarization

Mechanical: Ventricular systole ends; Ventricular diastole ends; Ventricular diastole begins; SL Valves close (Arterial P > Ventricular P)

T-P Segment EKG Electrical + Mechanical Events:

Electrical: No electrical events are occurring.

Mechanical: Atria + ventricles continue diastole; AV valves open (Ventricular P < Atrial P); Blood flows passively into Atria + Ventricles