Partial 4 - Cardiac Arrhythmias Flashcards
Four EKG characteristics of normal sinus rhythm
Regular narrow-complex
HR is between 60-100bpm
Each QRS complex is proceeded by a P wave
P wave is upright in lead II and downgoing in lead aVR
Mechanism of arrhytmogenesis include
Altered impulse formation
Altered impulse conduction
Altered impulse formation include
Increased automaticity which lead to tachyarrhythmias or decreased automaticity which leads to bradyarrhythmia’s.
Altered impulse conduction include
Reentry (Arrhythmia caused by not completed circuit) which lead to tachyarrhythmia, or Conduction blocks which leads to Bradyarrhythmia’s
Increased automaticity includes
Sinus tachycardia
Ectopic atrial tachycardia
Junctional tachycardia
Mechanism of reentry
There are two electrical pathways that make up reentry loop. We have one pathway (β-pathway) which has fast conduction and long refractory time, and one (α-pathway) with slow conduction with short refractory time (time it takes to conduct another signal). Reentry can be recognized on EKG due to the abrupt onset and termination of arrhythmia. The P wave of the first beat of the arrhythmia is different from the remaining beats of the arrhythmia.
AV nodal reentrant tachycardia (AVNRT)
It occurs when a re-entrant circuit forms within or just next to the atrioventricular node. AV nodal reentrant tachycardia is the most common regular supraventricular tachycardia
AV reentrant tachycardia (AVRT)
There are two types of AVRT; Orthodromic meaning that the impulse travels in the same direction as normal conduction, and antidromic which means that the conduction travels in opposite direction of normal conduction-
AVRT is most commonly associated with
Wolff–Parkinson–White syndrome
Atrial flutter is mostly caused by
a large reentrant circuit in the wall of the right atrium
EKG characteristics in atrial flutter include
A) sawtooth flutter waves at rate between 250-350 (300) bpm
(B) Flutter waves have constant amplitude, duration and morphology throughout the cardiac cycle
(C) There is usually a 2:1 or 4:1 block at the AV node, resulting in ventricular rates of either 150 or 75 bpm.
Atrial Fibrillation
is an abnormal heart rhythm characterized by rapid and irregular beating of the atria
Atrial Fibrillation is caused by
numerous wavelets of depolarization spreading throughout the atria simultaneously, leading to an absence of coordinated atrial contraction.
Atrial Fibrillation may lead to
Hemodynamic compromise
Systemic embolization
Symptoms (Palpitions, exercise intolerance, shortness of breath)
EKG characteristics in atrial fibrillation
Absent P waves
Presence of fine “fibrillatory” waves which vary in amplitude and morphology
Narrow QRS
Irregular ventricular response
AV-block deifinition
Heart block describes a type of arrhythmia that happens when the electrical signal gets held up and delayed, or blocked entirely at some point along the conduction system. These delays usually happen because of some sort of damage or fibrosis to the electrical conduction system.
Causes of AV block
Lev`s disease (idiopathic fibrosis)
IHD (ending with MI and scars).
First degree AV block
When signals is delayed but still makes its way to the ventricles. There is prolongation of PR interval more then 200 ms (normal 120-200 ms). There are usually no symptoms
First degree AV block EKG characteristics
Prolongation of the PR interval, which is constant
All P waves are conducted
Second degree AV block Type 1
Type 1 (Mobitz 1 or Wenckebach), happens when the PR interval becomes progressively longer with each beat until a P-wave is blocked completely and not conducted (disappears after some cycles), whereas RR interval actually shortens. All P waves are still conducted, and the signal reaches the ventricles.
There are usually no symptoms, but sometimes symptoms such as lightheadness, dizziness and syncope is seen.
Second degree AV block Type 2
In Type 2 (Mobitz II) is where there is constant PR interval (does not become longer) with intermittent failure to conduct that occurs randomly. A lot of times a ratio for the overall number of beats conducted to not-conducted is given, like 2:1 Mobitz II AV block.
Most people feel symptoms like, fatigue, dyspnea, chest pain, and syncope
Third degree AV block
Third degree AV block describes when the signal is completely blocked when moving from atria to the ventricles, every time. So even though atria go with 60 bpm, none of the signals make it down to the ventricles, and the ventricles, and the ventricles struggle along with escape beats at very slow rates, probably closer to 30 bpm
This type of AV block will often cause dizziness, syncope, angina and heart failure
Third degree AV block EKG characteristics
No relationship between P waves and QRS complexes
Relatively constant PP intervals and RR intervals
Greater number of P waves than QRS complexes
The conduction system of the heart is influenced by
Direct neural inputs (vagal stimulation)
Adrenergic agents (epinephrine)
Hypoxia
Potassium concentrations (hyperkalemia can block signal transmission altogether)
What is the most common cause of rhythm disorders?
Ischemic injury
Sinus bradycardia EKG
Every QRS is narrow and proceeded by P wave.
Causes of sinus bradycardia
Normal aging
15-25% of Acute MI especially those affecting inferior wall
Hypothyroidism and inflitrative diseases (sarcoid, amyloid)
Hypothermia and hyperkalemia
SLE, and collagen vascular diseases
Situations such as micturition and coughing
Drugs such as beta-blockers, digoxin, CCBs
Sinus tachycardia EKG
Often difficult to distinguish between P and T waves
Causes of Sinus tachycardia
Fever Hyperthyroidism Effective volume depletion Anxiety Pheochromocytoma Sepsis Anemia Exposure to stimulants (nicotine, caffeine) Hypotension and shock Pulmonary embolism Acute coronary ischemia and MI Chronic pulmonary disease Hypoxia
Sick sinus syndrome
Its a sinus dysfunction which result in bradycardia. It often results from tachy-brady syndrome where a burst of atrial tachycardia is then followed by a long, symptomatic sinus arrest.
Sick sinus syndrome is due to
Sinus fibrosis
S node atherosclerosis
Inflammation such as RA
Congenital and aquired heart disease and after surgery
Hypothyroidism or hypothermia or even drugs such a digoxin
Paroxysmal supraventricular tachycardia
It is a type of short-circuit arrhythmia which may result from AVNRT, or from an accessory pathway, which may occur as part of Wolff-parkingson-White syndrome
Atrial Fibrillation causes
Hypertension Hyperthyroidism CHF and CAD Mitral and tricuspid valve disease Hypertrophic cardiomyopathy COPD Obstructive sleep apnea Caffeine Digitalis/Digoxin Congenital (ASD) atrial septal defect
Premature atrial contraction
Its when the atria contract early due to depolarization from an ectopic focus. It is usually benign and there is no treatment
Premature ventricular contraction
These are very common and is abnormal heartbeats that originate in the ventricles and show up as tall and wide QRS complexes on ECG. They are usually asymptomatic
Premature ventricular contraction causes
Abnormal automaticity
Reentry
Non-sustained ventricular tachycardia
It is ventricular tachycardia that stops by itself within 30 seconds
Sudden Cardia Death definition
a natural, unexpected death occuring within 1 hour of the onset of symptoms
