ECG

P wave

The P wave represents the wave of atrail depolarization

p-R interval

The period of time from the onset of the P wave to the beginning of the QRS complex
normally ranges from 0.12 to 0.20 seconds in duration or(3-5 smal sequre)

represents the time between the onset of atrial depolarization and the onset of ventricular depolarization

Q wave
pathological Q wave means Qwave>1/3 R wave or >1 big sequre which ocurrce with old MI

QRS complex

The QRS complex represents ventricular depolarization.
The duration of the QRS complex is normally 0.06 to 0.1 seconds. (<2.5>abnormal duration
If the QRS complex is prolonged (> 0.1 sec), conduction is impaired within the ventricles.
This can occur with:

• bundle branch blocks


• a ventricular foci (abnormal pacemaker site) becomes the pacemaker driving the ventricle. Such an ectopic foci nearly always results in impulses being conducted over slower pathways within the heart, thereby increasing the time for depolarization and the duration of the QRS complex.
  

abnormal shape

the shape changes depending on

• which recording electrodes are being used.


• The shape will also change when there is abnormal conduction of electrical impulses within the ventricles

ST segment
The isoelectric period (ST segment) following the QRS is the time at which the entire ventricle is depolarized
The ST segment is important in the diagnosis of ventricular ischemia or hypoxia because under those conditions, the ST segment can become either depressed or elevated.

T wave
The T wave represents ventricular repolarization
Sometimes a small positive U wave may be seen following the T wave
This wave represents the last remnants of ventricular repolarization.
Inverted or prominent U waves indicates underlying pathology or conditions affecting repolarization.

Q-T interval
The Q-T interval represents the time for both ventricular depolarization and repolarization to occur, and therefore roughly estimates the duration of an average ventricular action potential. This interval can range from 0.2 to 0.4 seconds depending upon heart rate.
At high heart rates, ventricular action potentials shorten in duration, which decreases the Q-T interval.

Because prolonged Q-T intervals can be diagnostic for susceptibility to certain types of tachyarrhythmias, it is important to determine if a given Q-T interval is excessively long.
In practice, the Q-T interval is expressed as a "corrected Q-T (QTc)" by taking the Q-T interval and dividing it by the square root of the R-R interval (interval between ventricular depolarizations). This allows an assessment of the Q-T interval that is independent of heart rate.
Normal corrected Q-Tc intervals are less than 0.44 seconds.

• cause LQTS include the following:
• Drugs (many antiarrhythmics, tricyclics, phenothiazines, and others)
• Electrolyte abnormalities ( K+, Ca++, Mg++)
• CNS disease (especially subarrachnoid hemorrhage, stroke, trauma)
• Hereditary LQTS (e.g., Romano-Ward Syndrome)
• Coronary Heart Disease (some post-MI patients)
• paient may be develop arrythmia (dr m)