ECG2

16/12/2008 ECG Diag 2/ghazi

Principles of ECG Diagnosis2

Components of the ECG and there abnormalities

Dr Ghazi Radaideh, MD, FRCPRashid Hospital

Dubai - UAE


Reading 12-Lead ECG step-by-step (RAWIHI)

1. Rate, Rhythm and Regularity2. Determine the QRS Axis3. Evaluate the Waves (P,QRS,T ),

Intervals (PR,ST,QT)4. Evaluate for chamber Hypertrophy5. Look for myocardial Infarction and Ischemia6. Interpret the ECG


ObjectivesComponents of the Normal ECG and there Abnormalities

ECG Unit PQRST

Intervals & Segments:

ST

PQRS

T U

PR

QT

TP

Waves:


P waveP wave represents the

sequential activation of the right and left atria,

(Sinus node depolarization is too small in amplitude to be recorded from the body surface so it is not seen.)

The P-wave duration is divided into thirds to indicate the relative times of activation of the right (RA) and left (LA) atria.

LARARA&LA


QRS Complex

It begins at the onset of the Q wave and ends at the endpoint of the S wave.

It represents the simultaneous activation of the right and left ventricles, although most of the QRS waveform is derived from the larger LV.


QRS Complex Duration: < 0.10 sec(0.06 - 0.10s) Amplitude (voltage)is variable from lead to

lead and from person to person. This depends on:

Size of the ventricular chambers (i.e., the larger the chamber, the larger the voltage)

Proximity of chest electrodes to ventricular chamber (the closer, the larger the voltage)


Prolonged QRS Duration (>0.10s):

QRS duration 0.10 - 0.12s Incomplete right or left

BBB Nonspecific IVCD Some cases of LAFB

and LPFB

QRS duration > 0.12s Complete right or left

BBB Nonspecific IVCD Preexcitation Ventricular Ectopics

(e.g., VT, pacemaker rhythm)


The normal T wave always upright in leads I, II, V3-6 always inverted in lead aVR. The other leads are variable depending on the

direction of the QRS and the age of the patient


T wave changes low-amplitude (small, flattened) T waves abnormally tall T waves abnormally inverted T waves.


2.Abnormally tall T waves

Causes Hyperacute MI Hyperkalaemia, LBBB


Peaked T wave

HYPERKALEMIA


3.Abnormally inverted T waves


LVH with "strain


U Wave:(the most neglected of the ECG waveforms)

The normal U Wave Amplitude is usually < 1/3 T wave in

same lead Direction is the same as T wave in that

lead More prominent at slow heart rates Best seen in V2 and V3.

A U wave indicates that repolarization of the ventricles has occurred.


U wave


PR Interval

It represents the duration of theconduction through the atria to the ventricles.

It begins with the onset of the P wave and ends at the onset of the Q wave .

The best lead to use for measuring the PR interval is lead II.


PR IntervalNormal: 0.12 - 0.20s

In childhood 0.100.12 s

In adolescence 0.120.16 s

In adulthood 0.140.21 s

Short PR: < 0.12s

Prolonged PR: >0.20s


2.ST segment The ST segment lies

between the J point

J point

It represents the period between the end of ventriculardepolarisation and the beginning of repolarisation.

and the beginning of the T wave


"Primary" ST-T Wave Abnormalities

Causes: Ischemia, infarction and inflammation Drug effects (e.g., digoxin, quinidine, etc) Electrolyte abnormalities (e.g., hypokalemia) Neurogenic effects (e.g., subarrachnoid

hemorrhage causing long QT)


"Secondary" ST-T Wave changesCauses:

BBB LVH nonspecific IVCD WPW preexcitation PVCs, ventricular arrhythmias, and

ventricular paced beats

ST-T wave changes are due to alterations in the sequence of ventricular activation)


LVH with secondary ST-T change :


Causes of ST segment elevation "High take-off" Benign early repolarisation Acute myocardial infarction Left bundle branch block Left ventricular hypertrophy Ventricular aneurysm Coronary vasospasm/Printzmetal's angina Pericarditis Brugada syndrome Subarachnoid haemorrhage


Differential Diagnosis of ST Segment Elevation

1. Normal Variant:"Early

Repolarization" (usually concave upwards, ending with symmetrical, large, upright T waves)


Acute inferior MI


Differential Diagnosis of ST Segment Elevation (3)

3. Acute Pericarditis


ST segment elevation in leads V1 to V3 in patient with LVH


LBBB


ST segment depression

"downsloping Upsloping "horizontal",


Differential Diagnosis of ST Segment Depression

1.Normal variants or artifacts: Pseudo-ST-depression (wandering baseline due to

poor skin-electrode contact) Physiologic J-junctional depression with sinus

tachycardia (most likely due to atrial repolarization)

Hyperventilation- induced ST segment depression



2. Ischemic heart disease Subendocardial

ischemia Reciprocal changes

in acute Q-wave MI acute posterior MI



3.Non-ischemic causes of ST depression RVH (right precordial leads) or LVH (left

precordial leads, I, aVL) Digoxin effect Hypokalemia Mitral valve prolapse (some cases) CNS disease Secondary ST segment changes with conduction

abnormalities (e.g., RBBB, LBBB, WPW, etc)


3.QT interval It begins at the onset of

the Q wave and ends at the endpoint of the T wave.

QTIt represents the duration of the ventricular depolarisation/ repolarisation cycle.


QT interval Normal QT interval : heart rate dependent

Upper limit for QTc : < 0.46 s (460 ms). Long QT Interval:

> 0.46 sec for males

> 0.47 sec in females

QT

For practical purposes, the QT interval is prolonged if it clearly measures more than half the R-R interval


Corrected Q-T interval Bazett's formula:

Corrected Q-T interval = (measured Q-T / (square root (R-R interval in seconds )

Q-T

RR


Estimation of Q-T interval

1.RR= 25 small boxes

A QT > half of the RR interval is probably long.

2.QT = 16 small boxes

a quick way to estimate if the QT interval is long

RR

QT


ECG with marked QT prolongation

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