Which condition most commonly causes peaked notched or enlarged P waves on a EKG rhythm strip?

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The rate of paper [i.e. of recording of the EKG] is 25 mV/s which results in:

• 1 mm = 0.04 sec [or each individual block]
• 5 mm = 0.2 sec [or between 2 dark vertical lines]
• Distance between  Tick marks = 3 seconds [in the rhythm strip]

The voltage recorded from the leads is also standardized on the paper where 1 mm = 1 mV [or between each individual block vertically] This results in:

• 1 mm = 0.1 mV
• 5 mm = 0.5 mV [or between 2 dark horizontal lines]
• 10 mm = 1.0 mV

Heart rate calculation:

Normal range at rest is between 60-100 beats per minute [bpm].

The basic way to calculate the rate is quite simple. You take the duration between two identical points of consecutive EKG waveforms such as the R-R duration. Take this duration and divide it into 60. The resulting equation would be:

Rate = 60/[R-R interval]

A quicker way to obtain an approximate rate is

1. to go by  RR or PP interval. If it is 1 big box [0.2 secs] then the rate is 60/0.2 = 300 bpm. The rest of the sequence would be as follows.

   • 1 big box = 300 beats/min [duration = 0.2 sec]
   • 2 big boxes = 150 beats/min [duration = 0.4 sec]
   • 3 big boxes = 100 beats/min [duration = 0.6 sec]
   • 4 big boxes = 75 beats/min [duration = 0.8 sec]
   • 5 big boxes = 60 beats/min [duration = 1.0 sec]

2. Count the number of RR intervals between two Tick marks [6 seconds] in the rhythm strip and multiply by 10 to get the bpm. This method is more effective when the rhythm is irregular.

Rhythm can be quite variable. It could be

• Regular : RR interval constant
• Basically regular
  • Premature ectopic beat
  • Escape ectopic beat
• Regularly irregular : RR interval variable but with a pattern. Normal and ectopic beats grouped together and repeating over and over.
• Irregularly irregular. RR interval variable with no pattern, totally irregular

Normal:

Normal sinus rhythm [NSR]: indicates that the rate is between 60 and 100, inclusive, and that the P waves are identifiable and are of the same morphology throughout. The RR interval or PP intervals between beats are same.

Sinus arrhythmia: There is a cyclical acceleration of heart rate with inspiration and slowing  with expiration. The beat to beat interval is slightly different.The rhythm is regularly irregular, in the sense that there is a pattern to irregularity.  This is termed sinus arrhythmia.

P wave

Represents discharge of SA node and depolarization of both atria

Normal:

• The best lead to look at the P wave is V1.
• Normal P wave is upright and rounded
• The P wave in general should not be more than 1 box wide
• The P wave in general should not be more than  1 box tall.
• The p wave is biphasic in
• The P wave contour is constant

Abnormal:

• If  P wave exceeds the normal range for duration or voltage, it generally means that either or both atria is enlarged [hypertrophied]
• If P wave contour
  • Peaking of P wave [Voltage increase] suggests Right atrial hypertrophy
  • Broad slurred [increased duration]  suggests Left atrial hypertrophy
  • When biphasic the initial positive wave is prominent with RA hypertrophy and the negative deflection is prominent wit LA hypertrophy
  • If the P wave contour changes between beats it could mean that there is an ectopic atrial focus

QRS

QRS complex is a series of wave forms following P wave.

Naming convention:

• Q wave: first downstroke of the QRS complex. Usually very small or absent.
• R wave: first upward deflection of the QRS complex. Upward deflections occurring after an S wave are noted by a "prime mark" such as R'
• S wave: the first downward deflection occurring after the R wave.
• A monophasic negative QRS complex is called QS.

Normal

Duration: 0.08-0.12 seconds [2-3 horizontal boxes]

Contour is same between beats

Abnormal

Duration:

Delay in conduction through the ventricles leads to prolongation of QRS complex

• Prolonged: Bundle branch blocks, drug toxicity, electrolyte imbalance
• Shortened:  WPW

Contour

Change of contour between beats suggests ectopic foci

Abnormal  but constant contour suggests

• Bundle branch blocks
• Drug toxicity
• Electrolyte imbalance

Q wave

Normal:

Usually very small or absent

Normal in III and AVR .

Abnormal:

A Q wave is significant if it is greater than 1 box wide [0.04 secs] in leads other than III and AVR

Greater than 1/3 the amplitude of the QRS complex.

Greater than 1/4th of R wave

Abnormal Q waves: indicate presence of infarct

T wave

First upward deflection after QRS complex. Represents: ventricular repolarization

Normal:

In general, T waves are in the same direction as the largest deflection of the QRS [normally the R wave].

Negative in AVR

Inverted T waves in precordial leads V1, V2, V3 can be seen in normal, young athletes

Low T voltage changes may occur in the absence of any heart disease at all.

Abnormal:

T wave changes can be primary or secondary. 

Primary T wave change refer to abnormal repolarization

Secondary T wave changes are caused by QRS changes.  T wave changes caused by bundle branch block or ventricular hypertrophy are secondary.

Tall peaked T waves

Electrolyte imbalance =  Hyperkalemia causes tall peaked T waves.  overall maximum of 15 mV but this is not sensitive.  T wave looks like an isosceles triangle.

Low voltage T waves

• Hypokalemia causes low voltage T waves and prominent U waves.  T waves less than 1mV in the limb leads and less than 2mV in the precordial leads.

• low T voltage and sagging or flattened ST segments.  these changes may occur in the absence of any heart disease at all.

Inverted T waves

• Inverted T waves that are symmetrical, "round-shouldered" can be caused by coronary ischemia. especially when it occurs in a pattern as previously described for ST segment changes. .
• Inverted T waves in precordial leads V1, V2, V3 can be seen in normal, young athletes, as well as CNS diseases.

 U wave

What it represents is not certain.

This upright wave, when present, follows the T wave.

Abnormal:

The presence of  U waves may indicate Hypokalemia.

Hypokalemia is associated with flat T waves, U waves. U waves taller than T waves.

PR interval

Represents: atria to ventricular conduction time [through His bundle]  It includes P wave and PR segment.

Normal duration: 0.12-2.0 seconds [3-5 horizontal boxes]. This is measured from the onset of the P wave to the onset of the QRS complex regardless if the initial wave is a Q or R wave.

Abnormal duration:

Prolonged:

If the PR interval is greater than 0.2 sec, then an AV block is present. There are several types of AV blocks:

• 1st degree AV Block: PR>0.20 sec.
• 2nd degree AV Block: 2 types:
  1. Type I [Mobitz I or Wenckeback]: increasing PR interval until a QRS complex is dropped. It is usually benign.
  2. Type 2 [Mobitz II]: QRS dropped without any progressive increase in PR interval [i.e., PR interval is constant but still >0.20 sec].
• 3rd degree AV Block: atria and ventricles are electrically dissociated. Therefore, P waves and QRS complexes will occur independent of each other. As always, use the QRS complexes to determine heart rate.

Shortened:

A PR interval that is