Term
| What does the ECG at the skin surface detect? |
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Definition
| The electric dipole of the voltage field present as a depolarization wave passes along the cell |
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Term
| The ECG electrodes register a _________ signal when the depolarization wave is coming toward it, and __________ signal when the depolarization wave is receding away from it. |
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Definition
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Term
| Who reported the first ECG in 1903? |
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Definition
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Term
| The spread of a depolarization toward the recording electrode and away from the reference electrode results in a positive or negative deflection of the recording voltmeter? |
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Definition
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Term
| When a wave of repolarization moves toward the recording electrode, there will be a positive or negative deflection in the output from the recording device? |
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Definition
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Term
| A complete clinical ECG uses bipolar leads, unipolar leads, both, or neither? |
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Definition
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Term
| ECG Lead I records the potential difference between what? |
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Definition
| The left arm (+) and the right arm (-) |
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Term
| ECG Lead II records the potential difference between what? |
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Definition
| The left leg (+) and the right arm (-) |
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Term
| ECG Lead III records the potential difference between what? |
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Definition
| The left leg (+) and the left arm (-) |
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Term
| What is the angle of a positive Lead I? |
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Definition
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Term
| What is the angle of a positive Lead III? |
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Definition
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Term
| What is the angle of a positive Lead aVR? |
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Definition
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Term
| What is the angle of a negative Lead aVL? |
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Definition
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Term
| What do the precordial leads examine? |
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Definition
| Cardiac electrical activity in the horizontal plane (sternum to vertebral column) |
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Term
| Why do you usually not see atrial repolarization on a ECG? |
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Definition
| It occurs during ventricular depolarization, and the larger electrical forces associated with the greater muscle mass of the ventricles does not allow recognition of atrial repolarization on the body surface. |
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Term
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Definition
| The difference in conduction velocity due to fiber arrangement |
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Term
| What causes the P wave on an ECG? |
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Definition
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Term
| What causes the QRS complex on an ECG? |
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Definition
| Depolarization of the ventricles |
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Term
| What causes the T wave on an ECG? |
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Definition
| Repolarization of the ventricles |
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Term
| What is the normal pattern of waves on an ECG? |
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Definition
| P wave - QRS complex - T wave |
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Term
| What does the PR interval measure? What its the normal value? |
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Definition
The time required for depolarization to travel from the SA through the AV node and the His-Purkinje network 0.12-0.20 seconds |
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Term
| What does the QRS interval tell us? What is its normal value? |
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Definition
The time it takes for the ventricles to depolarize; tells us how healthy the His-Purkinje tree is 0.08-0.12 seconds |
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Term
| What does the ST segment show? |
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Definition
The interval when the ventricles are depolarized Corresponds to phase 2 of the intracellular action potential |
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Term
| What does the QT interval represent? |
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Definition
Total ventricular activation time Duration is variable, depending on heart rate at any given time |
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Term
| As cardiac mass (hypertrophy) increases, the voltage recorded on an ECG __________. |
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Definition
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Term
| What is decramental conduction? |
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Definition
The AV node slows down the electrical impulse from the SA node; gives time for the atrium to fill the ventricle during diastole; slows ventricular rate It takes 55 ms for a signal to go from AV node to myocardium |
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Term
| Under normal conditions, the area that depolarizes most rapidly and thus sets the heart rate is what? |
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Definition
| Sinoatrial node (SA node or sinus node) |
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Term
| Can activity in the AV node, bundle of His, bundle branches, and Purkinje network be detected by a surface ECG? Why or why not? |
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Definition
No, the electrical activity cannot be seen They are all too small |
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Term
| What is the first part of the ventricular myocardium to be depolarized? What wave does this correspond with? |
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Definition
The interventricular septum; from left to right Q wave |
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Term
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Definition
| The last area of the ventricles to be activated is the most superior-basal portion of the left ventricular free wall or the right ventricular outflow tract; by this time, the electrical activity of the heart is proceeding in a direction opposite to the feet, and thus a negative deflection in lead II |
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Term
| Why does the T wave point in the same direction as the QRS complex? |
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Definition
| Repolarization proceeds from epicardium to endocardium; although the net charge is reversed, the direction of the repolarization forces is also reversed |
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Term
| Normal sinus rhythm is present if the rate is between ______ and ______. |
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Definition
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Term
| What are the characteristics of first degree AV block? |
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Definition
| PR interval exceeds 0.20 seconds, but a P wave always precedes a QRS complex |
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Term
| What are the characteristics of second degree AV block? |
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Definition
| Some sinus rhythm impulses propogate through the AV node, some do not; a regular ration exists, such as 2 P waves for each QRS |
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Term
| What are the characteristics of third degree AV block? |
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Definition
| No relationship between P waves and QRS complexes; A back-up pacemaker develops in the ventricles; atria and ventricles each set their own rates since no action potentials originating in the atria can get to the ventricle; atrial rate is faster than the ventricular rate |
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Term
| Removal of all nervous input causes the heart rate to do what? |
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Definition
| Increase; suggests that vagal or parasympathetic tone predominates |
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Term
| What is atrial fibrillation? |
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Definition
Chaotic and unorganized atrial rhythm caused by numerous ectopic foci developing in the atria; can be due to changes in conduction pathways, refractory periods, etc.; no detectable P wave; hundreds of meandering "wavefronts" Rhythm is "irregularly irregular"; completely unpredictable |
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Term
| What is ventricular fibrillation? |
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Definition
| Fatal unless quickly stopped; ectopic focus develops in the ventricular muscle; QRS complex is usually bizarre, because depolarization occurs over muscle to muscle spread rather than the normal His-Purkinje network |
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Term
| What is a premature ventricular complex (PVC)? |
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Definition
| Occasional depolarization originating in the ventricle; a run of such beats is referred to as ventricular tachycardia |
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Term
| Myocardial infarction and ischemia of the heart are characterized by abnormalities in what portions of the ECG? |
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Definition
| Q waves, ST segment, and T waves |
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