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Phys Exam 2: Ch 11

The Normal ECG

QuestionAnswer
What is an ECG? 1. Detecting repetiitive changes in the flow of current thru the heart; 2. These changes correlate w/the cardiac cycle stages. 3. These changes are caused by waves of depolarization & repolarization that flow thru the cardiac muscle w/each heartbeat.
What is the P wave? Depolarization of the atria --> atria contract
What is the QRS wave? Depolarization of the ventricles --> ventricles contract
What is the T wave? Repolarization of the ventricles
Where is the repolarization of the atria within an ECG? Hidden within the QRS wave
What is the PQ interval? From the beginning of the P wave to the beginning of the QRS wave
What is the ST segment? From the end of the S wave to the beginning of the T wave
What is the QT interval From the beginning of the QRS wave to the end of the T wave
What is the J point? At the end of the S wave, when S returns to baseline
What do the vectors of the heart represent? Vectors represent amounts of energy and direction.
(Blank) is a measurement of heart vectors as they pass under an electrode The EKG
What causes the downward deflection in an EKG? When a positive electrical wave is moving away from an electrode
What causes the upward wave in an EKG? When a positive wave moves towards an electrode
Describe Lead I Negative to R arm, Positive to L arm; Measures QRS wave and pulse rate
Describe Lead II Negative to R arm, Positive to L leg
Describe Lead III Negative to L arm, Positive to L leg
What is Einthoven's Triangle? Visually correlates electrode placement and the heart
What is Einthoven's Law? The voltages measured by Lead I and Lead III equal the voltage measured by Lead II
If a patient has an enlarged ventricular muscle mass, what will the EKG from Lead I show? An enlarged QRS wave
If a patient has a decreased ventricular muscle mass (ex: from an old MI), what will the EKG from Lead I show? A reduced QRS wave
How do you determine pulse rate from an ECG? Measure the X-axis length b/n peaks, and calculate at 0.2 sec/dark bar, or 0.04 sec/light bar... OR... Estimate by counting the # of dark bars crossed, and use 300, 150, 100, 75, 60, 50." - Pulse rate at a glance.
What is the value of the large squares on the Y axis? What does this measure? 0.5mV; QRS wave
What is the value of the large squares on the X axis? The small squares? What does this measure? Large squares = 0.2sec, small squares = 0.04sec, it measures pulse rate
What is the electrical axis of the heart? The net vector of all of the vectors of the heart.
Created by: hclark86