EMG

Question 1

P wave

Answer 1

atrial depolarization

Question 2

PR interval

Answer 2

time for atrial depolarization and conduction from the SA node to the AV node. Normal duration is 0.12 to 0.20 second

Question 3

QRS complex

Answer 3

ventricular depolarization and atrial repolarization. Normal duration is 0.06 to 0.10 seconds

Question 4

QT interval

Answer 4

time for both ventricular depolarizatin and repolarization. Normally ranges from 0.20 to 0.40 seconds, depending on heart rate

Question 5

ST segment

Answer 5

isoelectric period following QRS when the ventricles are depolarized

Question 6

T wave

Answer 6

ventricular repolarization

Question 7

Sinus arrhythmia

Answer 7

A sinus rhythm, but with qukcening and slowing of impulase formation in the SA node resulting in a slight beat-to-beat variation of the rate

Question 8

Sinus arrest

Answer 8

A sinus rhythm, except with intermittent failure of either SA node impulse formation or AV node conduction that results in the occasional complete absence of P or QRS waves

Question 9

Premature atrial conductions (PAC)

Answer 9

Occur when an ectopic focus in the atrium initiates an impulse before the SA node;
The P wave is premature with abnormal configuration
Clinical significance:
1). PACS are very common and generally benign, but may progress to atrial flutter, tachycardia or fibrillation
2) May occur with a normal heart (from caffeine, stress, smoking, alcohol) and any type of heart disease

Question 10

Atrial flutter

Answer 10

An ectopic, very rapid atrial tachycardia;
Atrial rate of 250-350 beats per minute; ventricular rate dependent upon AV node conduction;
Saw-tooth shaped P waves (a;so known as flutter waves) are characteristic)
Clinical significance:
1) occurs with valvular diseas (especially mitral), ischemic heart disease, cardiomyopathy, hypertension, acute myocardial infarction, chronic obstructive lung disease, and pulmonayr emboli
2) signs and symptoms include palpitations, lightheadedness, and angina due to a rapid rate;
3) stagnation of blood may predispose to thrombi in the atria

Question 11

Atrial fibrillation

Answer 11

A common arrhythmia where the atria are depolarized between 350 and 600 times/min;
ECG shows characteristically irregular undulations of ECG baseline without discreate P waves
Clinical significance:
1) occurs in healthy hearts and in patients with coronary artery disease, hypertension, and valvular disease
2) symptoms may include palpitations, fatigue, dyspnea, lightheadedness, syncope, and chest pain
3) Stagnation of blood may predispose to thrombi in the atria

Question 12

1st degree atrioventricular block

Answer 12

PR interval is longer than 0.2s, but relatively constant from beat to beat
Clinical Significance: 1) no symptoms or significant change in cardiac function; 2) PR interval may become prolonged for many reasons including medications that suppress AV conduction

Question 13

2nd degree atrioventricular block

Answer 13

• AV conduction disturbance in which impulses between the atria and ventricles fail intermittently;
• Two major types: Mobitz type I block (also called Wenckebach block) and Mobitz type II block
  Clinical significance:
  1) Mobitz I - progressive prolongation of P-R interval until one impulse is not conducted (generally benign)
  2) Mobitz II - consecutive P-R intervals are the same and normal followed by nonconduction of one or more impulses (a more serious condition). If heart rate is slow, cardiac output will decrease with the blocked impulse. Also, 2nd degree AV block may progress to 3rd degree AV block

Question 14

3rd degree atrioventricular block (complete heart block)

Answer 14

• All impulses are blocked at the AV node and none are transmitted to the ventricles
• The atria and venticules are paced independently; atrial rate > ventricular rate
  Clnical significance:
  1) Considered a medical emergency requireing a pacemaker
  2) If the ventricular rate is too slow, the cardiac output drops and the patient may faint
  3) Common causes include degenerative changes of the conduction systems, digitalis, heart surgery, and acute MI

Question 15

Premature ventricular complex (PVC)

Answer 15

• Premature depolarization arising in the ventricles due to an ectopic focus
• Unifocal PVCs arise from the same ectopic focus and have the same configuration
• Multifocal PVCs arise from different ectopic foci and have different configurations
• On ECG, the P wave is usually absent and the QRS complex has a wide and aberrant shape
• Bigeminy - Normal sinus impulse is followed by a PVC
• Trigeminy - PVC occurs after every two normal sinus impulses
  Clinical Significance:
  1) A common arrhythmia that occurs in healthy and sideased hearts
  2) patient may be asymptomatic or have palpitations
  3) common causes include anxiety, caffeine, stress, smoking, and all forms of heart disease

Question 16

Ventricular tachycardia

Answer 16

• 3 or more consecutive PVCs at a ventricular rat of > 150 beats/minute
• P waves are absent and QRS complexes are wide and aberrant in appearance
  Clinical Significance:
  1) V-tach longer than 30 seconds is a life-threatening arrhythmia and requires immediate medical intervention
  2) Patients are not able to maintain an adequate blood pressure and eventually become hypotensive
  3) V-tach may degenerate into ventricular fibrillation causing cardiac arrest
  4) Common causes include: MI, cardiomyopathy, and valvular disease

Question 17

Ventricular fibrillation (v-fib)

Answer 17

• Ventricles do not beat in a coordinated fashion, but fibrillate or quiver asynchronously and ineffectvely
• No cardiac output; patient becomes unconscious
• ECG shows characteristic fibrillatory waves with an irregular pattern that is either coarse or fine
  Clinical Significance:
  1) A lethal tachyarrhythmia requires immediate defibrillation
  2) Additional measures include medications to support the circulation and intravenous antiarrhythmic agents
  3) Common causes include heart disease of any type, MI, and cocaine use

Question 18

Ventricular asystole

Answer 18

• Ventricular standstill with no rhythm
• ECG records a straight-line pattern
  Clinical Significance:
  1) Requires immediate defibrillation and/or medicatios to stimulate cardiac activity
  2) Common causes include acute MI, ventricular rupture, cocaine use, lightning strikes, and electrical shock

Question 19

ST segment depression

Answer 19

• A depressed ST segment is a sign of subendocardial ischemia, but also can be due to digitalis toxicity or hypolalemia
• The segment is evaluated relative to isoelectric baseline at 0.08 s after the J point (junction between the end of the QRS complex and the beginning of the ST segment)
• Deviations from the isoelectric baseline are expressed as ST segment depression of 1 mm, 2 mm, etc

Question 20

ST segment elevation

Answer 20

• Earliest sign of acute transmural infarction
• Can also indicate a benign early repolarization pattern in a nirmal heart
• Deviations from the isoelectric baseline are expressed as ST segment elevation of 1mm, 2mm, etc

Question 21

Q wave

Answer 21

• A characteristic marker of infarction; signifies the loss of positive electrical voltages due to necrosis
• A significant or abnormal Q wave is longer than 0.04 ms and larger than 1/3 the amplitude of the R wave

Question 22

T wave inversion

Answer 22

occurs hours or days after an MI as the result of a delay in repolarization produced by the injury
- May also occur with right and left bundle brance blocks, after a CVA, and as a normal juvenile T wave pattern in children and some adults