BMS100 - HEART LAB

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Click for a Conduction System Animation

• Resting Potential in a Neuron
• action potentials = electrical waves conducted by nerve and muscle fibers
  
• Action Potential in a Neuron
  1. sodium (Na+) flows in
     1. makes inside more positive
     2. depolarization = change in membrane potential (voltage) to a more positive value
     3. in muscle, depolarization causes contraction
  2. potassium (K+) flows out
     1. makes inside less positive, or more negative
     2. repolarization = return of membrane potential (voltage) to a negative value
     3. in muscle, repolarization causes relaxation
• Cardiac Action Potential
  1. sodium (Na+) flows rapidly into cell / depolarizes heart muscle fiber / initiates contraction
  2. calcium (Ca++) flows slowly into cell / maintains depolarization and state of contraction
  3. potassium (K+) flows out of cell / repolarizes heart muscle fiber / terminates contraction
• Cardiac Action Potential and EKG

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A. Lead II Electrocardiogram (EKG or ECG)

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For the basic electrocardiograms, use Lesson L05-ECG-1 with the electrodes plugged into channel 2.

Lead II Electrode Placement
Scrub skin before applying electrodes.
Do not remove the electrodes until told to do so.
• white electrode (+) on the right arm
• red electrode (-) on the left leg
• black electrode (ground) on the left arm

Measure the following and record the data on your Response Sheet.
Note any measurements not in the normal range.

Times and Intervals - use delta T from the pull-down menu for all (except heart rate - use bpm)


1. heart rate at rest = _______________________ beats per minute
   normal (in sinus rhythm): 60 to 100 beats per minute
   
   

   period of cardiac cycle = ___________________ seconds per cycle

   normal: approx. 0.8 sec.
   
   

   P wave duration (from beginning of P wave to end of P wave) = ________ sec.

   normal: 0.06 to 0.12 sec.
   
   

   PR interval (from beginning of P wave to R) = _____________ sec.

   normal: 0.12 to 0.20 sec.
   
   

   QRS duration = _____________ sec.

   normal: 0.06 to 0.12 sec.
   
   

   ST interval (from S to end of T wave) = _____________ sec.

   normal: approx. 0.3 sec.

   Note: if using automatic EKG machine, ST interval = QT interval - QRS duration
   
   

   T wave duration (from beginning of T wave to end of T wave) = ________ sec.

   normal: 0.12 to 0.16 sec.
   
   

   QT interval (from Q to end of T wave) = _____________ sec.

   normal: 0.30 to 0.35 sec.

Voltages - use p-p on pull-down menu


1. P wave voltage = ________ millivolts (mV) (normal: 0.1 to 0.3 mV)
   
   
2. QRS voltage = ________ millivolts (mV) (normal using limb leads: 1.0 mV)
   
   
3. T wave voltage = ________ millivolts (mV) (normal: 0.2 to 0.3 mV)

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B. The Electrical Axis Of The Heart



Leaving the self-adhesive electrodes on the skin, move the wires and record the Lead I and Lead III EKG’s.

Lead I Electrode Placement
• white electrode (+) on the right arm
• red electrode (-) on the left arm
• black electrode (ground) on the left leg

Lead III Electrode Placement
• white electrode (+) on the left arm
• red electrode (-) on the left leg
• black electrode (ground) on the right arm

1. Highlight a single Lead I QRS complex. Write the Max and Min amplitude values in the table on your Response Sheet. Be sure to include the sign (negative or positive) of the value.
2. Repeat for Lead III data. Write the values on your Response Sheet including the sign.
3. Sum the max and min values for Lead I and enter the value in the table.
4. Sum the max and min values for Lead III and enter the value in the table.
5. Plot the Net (sum of max + min) for Lead I (from the above table) on the graph by making a mark on the Lead I (0^o) line that corresponds to your data. From your mark, draw a straight line that is perpendicular to the Lead I (0⁰) line. This will be line A.
6. Repeat step 5 with the Net (sum of max + min) for Lead III. This will be line B.
7. Draw a third line, line C, from point 0,0 through the intersection of lines A and B. Continue this line until it intersects the arc.
8. The angle of line C, which is read from the arc, approximates the electrical axis of your heart. Write this value in the space provided on your Response Sheet.

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Fall 2010