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Systematic approach to EKG interpretation.


1.) Analyze the rate
2.) Analyze the rhythm
3.) Analyze the P waves
4.) Analyze the P-R interval
5.) Analyze the QRS complex


The ECG is recorded at a speed of ?

25 mm/sec,


voltages are calibrated so that 1 mV =

10 mm in the vertical direction.


each small 1-mm square =

0.04 sec and 0.1 mV


The P wave represents the wave of depolarization that spreads from the ?

SA node throughout the atria, and is usually 0.08 to 0.1 seconds (80-100 ms) in duration.


The brief isoelectric (zero voltage) period after the P wave represents what ?

- the time in which the impulse is traveling within the AV node (where the conduction velocity is greatly retarded)


Atrial rate can be calculated by what ?

-determining the time interval between P waves.


The period of time from the onset of the P wave to the beginning of the QRS complex is termed the P-R interval, which normally ranges from 0.12 to 0.20 seconds in duration. This interval represents what?

-the time between the onset of atrial depolarization and the onset of ventricular depolarization.


If the P-R interval is >0.2 sec, there is an ?

-AV conduction block, which is also termed a first-degree heart block if the impulse is still able to be conducted into the ventricles.


The QRS complex represents what?

-ventricular depolarization.


Ventricular rate can be calculated by determining

-the time interval between QRS complexes, which is done by looking at the R-R intervals.


The duration of the QRS complex is normally ?

0.06 to 0.1 seconds.


If the QRS complex is prolonged (> 0.1 sec), conduction is impaired within the ventricles. This can occur with?

bundle branch blocks or whenever a ventricular foci (abnormal pacemaker site) becomes the pacemaker driving the ventricle.


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.


The isoelectric period (ST segment) following the QRS is the time at which ?

-the entire ventricle is depolarized and roughly corresponds to the plateau phase of the ventricular action potential.


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.


The T wave represents ?

-ventricular repolarization and is longer in duration than depolarization (i.e., conduction of the repolarization wave is slower than the wave of depolarization).


U wave may be seen following the T wave This wave represents what?

-the last remnants of ventricular repolarization.


Inverted or prominent U waves indicates an underlying pathology or conditions affecting what?



The Q-T interval represents what?

- the time for both ventricular depolarization and repolarization to occur, and therefore roughly estimates the duration of an average ventricular action potential.


QT 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.


prolonged Q-T intervals can be diagnostic for susceptibility to certain types of



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 completing the following formula?

(Q-T interval)/(√R-R )

This allows an assessment of the Q-T interval that is independent of heart rate.


R-R interval =

(interval between ventricular depolarizations


Normal corrected Q-Tc intervals are less than?

0.44 seconds.