Lecture 11: Cardiac arrhythmias Flashcards
1
Q
What are some causes of cardiac arrhythmias?
A
- Increased/ decreased sinus node automaticity
- Escape rhythms: heart beats from a different pacemaker
- Enhanced automaticity of latent pacemakers (ectopic beats/rhythms)
- E.g. junctional escape rhythm
- Premature junctional contraction
- Triggered activity after depolarizations
- Could be produced by low potassium (hypokalemia) n drug toxicity
- Conditional abnormalities
- Areas of the heart where beat can’t be conducted
- Unidirectional block n re-entry: allows the heart to beat at enormous rates
2
Q
What is sinus tachycardia?
A
- > 100 BPM, 100 - 180 (faster heart rate than normal)
- Driven by the sinus node
- CAUSE: decreased vagal/increased sympathetic tone
- Can be pathological
- Acute hyperthyroidism
- Heart failure
- Hemorrhage [heart beats quicker to compensate for lack of blood]
- Fever
- Anemia
- Hypovolemia
- Can be pathological
- Can be seen in startles/frightened individual or during normal exercise
- Never treat sinus tachycardia but treat the cause
3
Q
What is sinus bradycardia?
A
- <60bpm
- Tolerate as low as 45pm
- Normally during sleep/fit athlete
- CAUSE
- Blood supply to SA node interrupted following MI
- Drug induced (e.g. beta blockers, digoxin)
- Hyperkalemia, hypothyroidism, hypothermia
- Treat underlying condition, stop medication
4
Q
What is sinus arrest?
A
- Missing beats (PQRST complex) otherwise normal ECG
- Sinus pause (1-2 missing beats), arrest (3 or more)
- Maybe no symptoms (depends on numeber missing)
- CAUSE
- Drug induced
- MI
- SA disease
- Increased vagal tone
- Can cause faint [no blood supply to the brain]
5
Q
What is sick sinus syndrome?
A
- SA node fails to excite the atria in a regular manner → slow resting heart raet
- Heart rate does not increase w exercise
- Can be
- Drug induced
- Intense vagal activity
- Degeneration of the pacemaker following ischemia
- TREATMENT: insertion of artificial pacemaker
6
Q
What is sinus arrhythmia?
A
- Normal phenomenon
- Subtle changes in heart rate w each respiratory cycle
- CAUSE: fluctuations in vagal activity
- Inspiration → accelerates heart reat
- Expiration → slows heart rate
- Normal in children n young adults disappear w age
7
Q
What are premature ventricular contractions (PVCs)?
A
- Ventricular ventricles are contracting separately from the normal beat
- % of PVCs typically increase w age
- CAUSES
- Medications that hv stimulant effect on the heart
- Caffeine
- Alcohol
- Illicit drugs
- States of heightened sympathetic activity (e.g. stress, exercise)
8
Q
What are the 2 major causes of conduction abnormalities?
A
- Depolarization
- Injured tissue → altered balance of ionic currents → inactivation of Na n Ca channels → poor conductance → slow spread of conduction
- RESULT: less excitable (partial block) or completely inexcitable (complete conduction block)
- Abnormal anatomy
- Presence of aberrant conduction pathway
- E.g. can bypass AV node which normally imposes conduction delay
- Second conduction pathway b/w atria n ventricles predispose to supraventricular arrhythmias
9
Q
What is Wolff-Parkinson-White syndrome?
A
- Example of abnormal anatomy
- Abnormal pathway
- NORMAL
○ AV node
○ Down to ventricles
○ Disspitate out - SYNDROME
○ Beat can come backwards into atria
○ Can prematurely get into the ventricles - ECG result
○ Short PR interval
○ Wide QRS [faster accessory pathway + AV node] - If the heart beats faster, there is a loop of activity
Goes back into the atria to re-excite -> tachycardia [heart will stop beating much more quickly, beats persisting]
10
Q
What is first-degree block?
A
- Long PR interval
- Beat gets to repolarize the atria -> large delay AV node
- Longer delay b/w P n QRS
- Still 1:1 relation b/w P n QRS
- Benign condition
- Many young people will show this pattern esp during sleep when there is high vagal tone
Does not require treatment
11
Q
What is second-degree block — Mobitz Type I?
A
- Slow increase in lengthening of PR interval
- No QRS
- Fails n restarts again
- PR interval lengthens until AV node fails completely
- Atrial rhythm is regular
- Benign condition
- Often no symptoms can be dizzy [not enough blood supply to tissue]
12
Q
What is bundle branch block (BBB)?
A
- NORMAL
○ Heart beat goes down 2 bundles of His then go across ventricles to depolarize -> contraction- Bundle branch block
○ Bundles fail
○ Only goes down one side of the heart
○ Will spread across the heart -> will still get contractions on the other side of the heart
○ Causes the QRS to widen [slow depolarization[
Slow contraction -> loss of efficiency
- Bundle branch block
13
Q
What is second-degree block — Mobitz Type II?
A
- PR interval consistent but every Nth cycle ventricular depolarization is missing
- May progress to complete heart block
14
Q
What is third degree (complete) block?
A
- Failure of conduction b/w atria n ventricles
- Supraventricular impulses no longer trigger ventricular contraction
- Causes
○ Acute MI
○ Drug toxicity
○ Chronic degeneration w age - Atria can be beating relatively normally but ventricles still beat bc they still get beat from latent pacemakers
- If no beat getting to the ventricles, they still beat but it’s not from the SA node
- Escape rhythm
Heart rhythm initiated by lower centers when the SA fails to initiate impulses when it’s rhythmically depressed or when it’s completely blocked
15
Q
What are the symptoms of third degree (complete) block?
A
- Bradycardia
- Signs of congestive heart failure (decreased CO)
- Tachypnea or respiratory distress
- Rales
- Jugular venous distention
- Patients may hv signs of hypoperfusion
- Altered mental status
- Hypotension
- Lethargy
- In patients w concomitant myocardial ischemia or infarction
- Signs of anxiety (e.g. agitation or unease)
