WEEK 2: CH10-EXCITATION/CONDUCTION, CH 11-ECG, CH 13-Cardiac Arrhythmias

Question 1

Normal Impulse Conduction:

1. Sinus (Sinoatrial; S-A) node&raquo_space;>
2. Atrioventricular (A-V) node&raquo_space;>
3. A-V Bundle (bundle of His)&raquo_space;»
4. R & L Bundle Branches&raquo_space;»
5. Purkinje fibers

Answer 1

KNOW

Question 2

Control of Excitation (Pacemakers of the Heart)
1. S-A node - _______ pacemaker with an
intrinsic rate of 70 - 80 beats/minute.

2. A-V node - Back-up pacemaker with an
   intrinsic rate of ____-______ beats/minute.
3. Purkinje fibers - Back-up pacemaker with
   an intrinsic rate of _____-______ beats/min

Answer 2

Dominant

40 - 60

15 - 40

Question 3

Ectopic Pacemaker (_______ Pacemakers)

• Ectopic Pacemaker is located somewhere other than the S-A node and causes an abnormal sequence of events as noted on an ECG.
• Block between S-A node and A-V node
• A-V block or A-V bundle block

Answer 3

Abnormal

Question 4

Control of Excitation and Conduction

• Parasympathetic Stim.
– Vagus nerve
– Acetylcholine
– Innervate S-A and A-V

• Sympathetic Stim.
– Norepinepherine
– ↑ rate of conduction
– ↑ force of contraction

Answer 4

KNOW THESE

Question 5

The ECG Paper

• Horizontally
– One small box = 0.04 s
– One large box = 0.20 s

• Vertically
– One small box -= 0.1 mV
– One large box = 0.5 mV

Answer 5

KNOW

Question 6

Flow of Electrical Current around Heart

• Electrical impulse arrives in the septum
• Strong _______ on insides of ventricles
• Strong ________ on outer walls
• Current flows in an elliptical pattern from (₋) base to (+) apex

Answer 6

electronegativity

electropositivity

Question 7

Causes of Arrhythmias

1 • Abnormal rhythm of the pacemaker.
2 • Shift of pacemaker from sinus node (S-A node)
3 • Blocks at different points of transmission of the cardiac impulse.
4 • Spontaneous generation of abnormal impulses from any part of the heart.

Answer 7

KNOW

Question 8

Abnormal Sinus Rhythms
1. Bradycardia—“slow heart” (HR ˂ 60 bpm)
• Present in athletes who have↑ SV (strong contract)
2. Tachycardia—“fast heart” (›100 bpm)
• Conditions that can elevate HR—exercise, fever, stress, shock, blood loss, weakened myocardum (congestive heart failure).
3. ____ ________—the sinus rhythm is influenced by parallel vagus nerve activity during breathing. The main difference is the irregular distance between T wave and P wave. Often seen in children. VARYING RATE

Answer 8

Sinus Arrhythmia

Question 9

Arrhythmias from Block of Impulse within Conduction Pathway X4

____________ Block—the impulse is blocked before it enters the R atria so no P wave present. A-V node becomes pacemaker—QRS and T are evident but slowed. This is a very rare condition.

Answer 9

1. Sinoatrial

Question 10

Arrhythmias from Block of Impulse within Conduction Pathway X4

________-Degree Heart Block—P-R interval ›0.20
• Referred to as “INCOMPLETE” heart block because
the signal is delayed rather than totally blocked.
• Acute Rheumatic Heart Disease—causes
inflammation of A-V node.

Answer 10

2. First

Question 11

Arrhythmias from Block of Impulse within Conduction Pathway X4

___________-Degree Heart Block—when the P-R interval
is 0.25-0.45. Some impulse pass through the A-V
bundle but others do not causing “DROPPED BEATS”.
• P wave but no QRS complex or T wave.
• Failure of conduction system from atria to ventricles.
• Other rhythms develop (2:1, 3:1; 3:2) atria : ventricle

Answer 11

3. Second

Question 12

Arrhythmias from Block of Impulse within Conduction Pathway X4

_________-Degree Block (Complete A-V Block)—complete LACK of –synchronization– between atria & ventricles.
• Ventricles spontaneously establish own signal.
• P-P interval is consistent (100 bpm) but there is dissociation with QRS complex and T wave.
• R-R Interval is consistent—40 bpm

Answer 12

4. Third

Question 13

Stokes-Adams Syndrome

• ___________ A-V block comes and goes.
• Ventricles stop contracting for 5 to 30 seconds because of over-drive suppression.
• Person faints because of lack of blood flow to brain.
• Ventricular escape occurs with a an A-V node or A-V bundle stimulus (15-40 bpm).
• Pacemaker to right ventricle are implanted

Answer 13

Complete

Question 14

Premature Contractions:

• Result from “ectopic foci” –outside the normal conductive pathway emitting a signal at ___ _____ during the cardiac rhythm.
• Causes of ectopic foci:

a) local areas of ischemia—lack of blood flow.
b) irritation of cardiac muscle (calcified plaque).
c) toxic irritation from drugs, caffeine, or nicotine.
d) mechanical initiation of PVC during catheterization of right ventricle.

Answer 14

odd times

Question 15

Premature Atrial Contractions (PACs)

• Can occur in healthy individuals and even athletes.
• Most often caused by conditions ranging from lack of
sleep, too much coffee, smoking, alcoholism, and various types of drugs.

Answer 15

Pulse Deficit :

–can occur with PACs because ventricles do NOT fill
so SV ↓ thus the pulse wave in the peripheral arteries may NOT be strong enough to feel, so you may miss counting some beats.

Question 16

Re-entrant Pathways—often cause _____ _______

Answer 16

atrial flutter

Question 17

Premature Atrial Contractions (PACs)

1._______ ________—the affected atria contracts at a rate
of 200-350 bpm because of re-entry wave,
• Signals reach A-V node too rapidly for all these
impulses to be passed on to the ventricles
• Both the A-V node and A-V bundles are in a
refractory period during many of the impulses.
• P waves are strong but QRS and T follow every 2 or 3

Answer 17

Atrial Flutter

Question 18

Premature Atrial Contractions (PACs)

2. ____ __________—activation of atria is irregular and
   chaotic so atria becomes useless as a primer pump
   for the ventricles—efficiency drops by 20-30%.
   • Causes include atrial hypertrophy resulting from
   valve dysfunctions that prevent emptying or from
   ventricular failure because of damming of blood.

Answer 18

Atrial Fibrillation

Question 19

Premature Atrial Contractions (PACs)

3. A-V Node or A-V Bundle (Junction Rhythms)

a–premature contraction originate in one of these junction sites.

b– P wave occurs late so occurs in QRS and distorts QRS or it comes after QRS and is _________

c– P wave travels backward into atria (retrograde direction).

Answer 19

inverted

Question 20

Premature Atrial Contractions (PACs)

4. _______ Ventricular Contractions (PVCs)—
   range from single PVCs which can be benign up to serious
   up to multiple PVCs from re-entrant signals from ischemia or infarct.
   • The QRS complex has an abnormal form because one
   side depolarizes ahead of the other.
   • T wave following QRS complex is inverted.

Answer 20

Premature

Question 21

Premature Atrial Contractions (PACs)

5. _______ _______________ —is a result of
   re-entrant stimuli leading to circular
   activation. Therefore, the ventricles are
   stimulated to contract at a rate over 120 bpm.
   • Caused by ischemia or myocardial infarction.
   • If not addressed can quickly lead to V-Fib.

Answer 21

Ventricular Tachycardia (V-Tach)

Question 22

6. ________________ _________—ventricular
   depolarization occurs chaotically so some parts
   contract while other parts are relax so little blood pumped out of heart.
   • Has multiple re-entry loops from a dilated heart muscle (cardiac hypertrophy) or if diseased heart (ischemia or infarction).

Answer 22

Ventricular Fibrillation (V-Fib)