3. Electrical Activity of the Heart:
⢠Under normal circumstances, the conduction system
first stimulates contraction of the atria and then the
ventricles.
⢠The synchronization of the atrial and ventricular
events allows the ventricles to fill completely before
ventricular ejection, thereby maximizing cardiac
output.
⢠This synchronization is provided by the two
specialized electrical cells, the nodal cells and the
Purkinje cells, which help in automaticity,
excitability and conductivity.
4. ⢠The SA node, the primary pacemaker of the
heart, is located at the junction of the superior
venacava and the right atrium.
⢠The normal sinus rhythm occurs when:
ďźit originates in SA node
ďźatrial and vantricular rates are regular
ďź60-100 bpm
ďźconsistently configured P wave
ďźPR interval 0.12-0.20 seconds, constant
ďźQRS interval 0.04-0.10 seconds, constant
5.
6. ⢠SA node initiate the action potential of the
heart followed by the a very specific sequence
and timing for the conduction of action
potentials to the rest of the heart.
⢠Atrial internodal tracts and atria
ďąaction potential spreads from the SA node to the
right and left atria via the atrial internodal
tracts.
ďąsimultaneously, the action potential is
conducted to the AV node.
7. ⢠AV node
ďąconduction velocity through the AV node is
considerably slower than the other cardiac
tissues.
ďąSlow conduction through the AV node ensures
that the ventricles have sufficient time to fill with
the blood before they are activated and contract
ďąIncrease in conduction velocity of the AV node
can lead to decreased ventricular filling and
decreased stroke volume and cardiac output
8. ⢠Bundle of His, Purkinje system, and
Ventricles
ďąFrom the AV node, the action potential enters
the specialized conducting system of the
ventricles.
ďąThe action potential is first conducted to the
bundle of his through the common bundle. It
then invades the left and right bundle branches
and then the smaller bundles of the Purkinje
system.
ďąConduction through the His-Purkinje system is
extremely fast, and it rapidly distributes the
action potential to the ventricles.
9. ⢠The electrical stimulation of the muscle cells of
the ventricles in turn causes the mechanical
contraction of the ventricles(systole). The cells
repolarize and ventricles then relax(dystole).
⢠Once an electrical cell generates an electrical
impulse, this electrical impulse causes the ions
to cross the cell membrane and causes the action
potential, also called depolarization.
⢠Repolarization is the return of the ions to their
previous resting state, which corresponds with
relaxation of the myocardial muscle
10. Arrhythmias:
⢠Arrhythmias (also referred as dysrhythmia) are
disorders of the formation or conduction(or both) of
the electrical impulses within the heart, altering the
heart rate, heart rhythm, or both and potentially
causing altered blood flow.
⢠Arrhythmias can cause sudden death, syncope, heart
failure, dizziness, palpitations or no symptoms at all.
11. Pathogenesis of Arrhythmia:
⢠Pathological heart disease
⢠Some physical conditions
⢠Other systemic disease
⢠Electrolyte disturbance and acid-base imbalance
⢠Physical and chemical factors and toxicosis
14. A. Abnormal Heart Pulse Formation
1. Sinus node arrhythmia:
a. Tachydysrhythmia
b. Bradydysrhythmia
15. a. Tachydysrhythmia:
⢠Heart rate>100 bpm
⢠P wave:normal and consistent, always in front of
QRS, but may be buried in the preceding T wave
⢠QRS and PR interval:normal
⢠Conduction:normal
⢠Rhythm:regular or slightly irregular
16. ⢠The underlying causes include:
ďCHF
ďHypoxia
ďPhysical conditions:exercise, anxiety, alcohol,
stress, pain, increased temperature
ďCirculating catecholamines
⢠Its treatment includes indentification of the
underlying cause and correction.
17.
18. b. Bradydysrhythmia:
⢠Heart rate<60 bpm (40-59 bpm)
⢠P wave:normal
⢠Conduction: PR interval normal or slightly
prolonged at slower rates
⢠This rhythm is seen as a normal variation in
athletes, during sleep, or in response to a vagal
maneuver.
⢠Treatment includes:
ďTreat the underlying cause,
ďAtropine,
ďIsuprel, or
ďArtificial pacing if patient is hemodynamically
compromised
19.
20. Sick sinus syndrome(SSS):
⢠SSS or sinoatrial disease is usually caused by
idiopathic fibrosis of the sinus node.
⢠Other causes include IHD, cardiomyopathy, or
myocarditis.
⢠Patients present episodes of sinus bradycardia,
sinus arrest, paroxysmal supraventricular
tachycardia or tachy-brady syndrome.
22. a. Atrial Flutter:
⢠Atrial flutter is caused by a re-entrant rhythm in
either the right or left atrium.
⢠Typically initiated by a premature electrical
impulse arising in the atria, atrial flutter is
propagated due to differences in refractory periods
of atrial tissue. This creates electrical activity that
moves in a localized self-perpetuating loop.
⢠Atrial flutter makes a very distinct "sawtooth"
pattern on an ECG.
24. b. Atrial fibrillation:
⢠Most common abnormal heart rhythm.
⢠Rate: atrial rate usually between 400-650 bpm
⢠P wave: not present; wavy baseline is seen instead
⢠QRS: normal
⢠Rhythm:irregularly irregular(hallmark of this
dysrhythmia)
⢠S/S: irregular palpitations, fatigue, malaise,
shortness of breathe, sweating, chest pain
⢠Treatment includes:
ďąDigoxin to slow the conduction rate
ďąCardioversion may also be necessary
25.
26. 3. Atrioventricular Junctional
Arrhythmia:
a. Premature junctional complex
b. Juctional rhythm
c. Non-paroxysmal junctional tachycardia
d. Atrioventricular nodal reentry tachycardia
27. a. Premature Junctional Complex
⢠It is an impulse that starts in the AV nodal area
before the next normal sinus impulse reaches the
AV node.
⢠Causes: digitalis toxicity, heart failure, and CAD
⢠P wave: may be absent, may follow the QRS or
may occur before the QRS.
⢠PR interval<0.12 seconds
⢠Treatment: according to the underlying cause
28.
29. b. Junctional Rhythm:
⢠It occurs when the AV node, instead of the SA
node, becomes the pacemaker of the heart.
⢠When the SA node slows, or when the impulse
cannot be conducted through the AV node then the
AV node automatically discharges an impulse.
⢠A junctional rhythm not caused by complete heart
block has the following features:
30. ⢠The treatment is the same as for sinus bradycardia. Emergency
pacing may be required.
31. c. Non-paraoxysmal Junctional
Tachycardia:
⢠Junctional tachycardia is caused by enhanced
automaticity in the junctional area, resulting in
rhythm similar to junctional rhythm, except at a rate
of 70-140 bpm.
⢠Non-paroxysmal junctional tachycardia is a related
but rare pattern of arrhythmia that can be observed
in the setting of digoxin toxicity .
⢠Cardioversion is not effective as it causes increase in
the ventricular rate.
32.
33. d. Atrioventricular Nodal Reentry
Tachycardia(AVNRT):
⢠It occurs when an impulse is conducted to an area
in the AV node that causes the impulse to be
rerouted back into the same area over and over
again at a very fast rate.
⢠Each time the impulse is conducted through this
area, it is also conducted down into the ventricles,
causing a fas ventricular rate.
34. ⢠AV rate: atrial rate usually 150-250; ventricular
rate usually 120-200
⢠AV rhythm: regular; sudden onset and
termination of tachycardia
⢠P wave:usually very difficult to disern
⢠PR interval: if P wave is infront of the QRS, the
PR interval is less than 0.12 seconds.
35.
36. 4. Ventricular Arrhythmia:
a. Premature ventricular complex
b. Ventricular tachycardia
c. Ventricular fibrillation
d. Idioventricular rhythm
e. Ventricular asystole