ECG leads, waves, segments + abnormalities

Waveform

movement away from the baseline in either positive (above) or negative (below) direction

Segment

line between waveforms

Complex

several waveforms

Interval

waveform + segment

P-wave represents

atrial depolarization

P-wave height

<2.5 mm

P-wave duration

<0.12 s

P-wave is ____ and and best seen in leads

positive; II, III, aVF

P-wave is biphasic in lead

V1

Notched P-wave

P mitrale → LA enlargement (LAE)

Peaked P-wave

P pulmonale → RA enlargement (RAE)

Inverted P-wave

negative P → ectopic pacemaker (AV node)

QRS complex represents

ventricular depolarization

Q wave

depolarization of IVS, always (-), < 30% R

R wave

depolarization of RV and LV, always (+)

S wave

depolarization of RV and LV, always (-)

QRS duration

0.075-0.11 sec

QRS amplitude

varies among leads and can be (+), (-), or biphasic depending on the leads

The duration of QRS with an impulse originating in an ectopic pacemaker (Purkinje or ventricular)

 >0.12 sec

QRS duration with the impulse originating in the bundle branch

0.11 - 0.12 sec = incomplete BBB

QRS duration > 0.12 sec

wide QRS, complete BBB

Low amplitude QRS

< 5 mm or < 0.5 mV

abnormally tall R-wave

RV enlargement

abnormally deep S-wave and abnormally tall R-wave

LV enlargement

T-wave represents

ventricular repolarization

T-wave Direction

usually same to the QRS

T-wave Height in limb leads

< 5 mm

T-wave Height in precordial leads

< 10 mm

T-wave following an abnormal QRS

usually moves in a direction opposite the QRS

T-wave inversion (1-5mm)

myocardial ischemia

Peaked T-wave

hyperkalemia

Low amplitude T-wave

hypokalemia, hypomagnesemia

Deeply inverted T-wave (5-10mm)

brain hemorrhage, stroke, antidepressant medication

U-wave represents

late repolarization of the Purkinje fibers

U-wave is most evident in

precordial leads V2, V3

U-wave direction

same like T-wave

U-wave Height

low amplitude < 0.1 mV

Inverted U-waves in leads V2-V5

acute ischemia and HTN

Prominent U-waves

CNS disease, hypokalemia, long QT syndrome

and as side effect of antiarrhythmic medication

PR segment represents

the spread of the electrical stimuli from the AV node through the AV bundle, RBB, LBB and the Purkinje fibers

ST segment represents

early phase of repolarization of the ventricles

J point

junction where QRS complex and ST segment meet

NSTEMI

depression ; > 0.5 mm = Ischemia

STEMI

elevation; > 1 mm at J-point = Injury/Infarction

Other ST segment changes

Hyperkalemia, Acute pericarditis, LV aneurysm, BBB, Digitalis

PR interval

P-wave + PR segment

PRI reflects

total supraventricular activity

PRI duration

0.12s

Prolonged PRI

delay in conduction through the atria, AV node or AV bundle

Shortened PRI

ectopic atrial pacemaker or abnormal conduction pathway to the ventricle

QT interval

QRS complex + ST segment + T-wave

QT interval represents

total ventricular activity

QT interval duration

0.40s

QTc

corrected QT, adjusted to HR

QTc > 0.50 sec

considered dangerous because of risk for fatal ventricular arrhythmias

R-R interval

R-wave to consecutive R wave, evaluates ventricular rhythm

P-P interval

beginning of P-wave to beginning of consecutive P-wave, evaluates atrial rhythm

Artifacts

distortion of an ECG tracing by electrical activity of non cardiac origin

Motion artifact

poor contact of electrodes due to inadequate skin preparation, patient movement

60-cycle interference

external (broken ECG lead wires, external chest compressions) or internal (shivering, muscle tremors)

Wandering baseline

may occur because of regular respiratory movements