Cardiac Dysrhythmias

Abnormal Rates of Sinus Rhythm
- Sinus Tachycardia
- Sinus Bradycardia
- Sinus Arrhythmia
- Sinus Arrest
Abnormal Site of Impulse Rhythm
- Atrial Dysrhythmias
  - Premature atrial complexes
  - Atrial flutter
  - Atrial fibrillation
- Ventricular Dysrhythmias
  - Premature ventricular complexes
  - Ventricular tachycardia
  - Ventricular fibrillation
Disturbances of Atrioventricular Conduction
- First Degree Block
- Second Degree Block
  - Type I- Mobitz type I, Wenckebach
  - Type II- Mobitz type II
- Third degree Block

Cardiac Dysrhythmias: Mechanisms

Dysrhythmia (arrhythmia): a cardiac rhythm abnormality affecting impulse generation or conduction
Three mechanisms of Dysrhythmia:
- Abnormalities in rate of impulse
  - Inappropriate automaticity
  - Triggered activity
- Abnormalities in impulse conduction
  - Reentry (most common mechanism)

Inappropriate Automaticity

Inappropriate automaticity
- Cells other than autorhythmic cells gain ability to depolarize.
- Due to abnormal ion fluxes
  - Ischemia- ATP deficit causes electrolyte imbalance
  - Electrolyte imbalance- Hypokalemia
- Can trigger an AP causing extrasystoles (extra heartbeats between normal beats)

Triggered Activity

Triggered activity
- Early afterdepolarization and Late afterdepolarization
- Afterdeoplarization- a depolarization that occurs before or after the repolarization phase
  - Many causes: bradycardia, hypokalemia, hypoxia
- Early and late afterdepolarizations can result in extrasystoles
- Early afterdepol: A second R wave occurs on top of the T wave.
- Late Afterdepol: A second R wave occurs just after the T wave.

Reentry

Reentry (most common)
- Depolarization of a patch of tissue that has just repolarized from the previous wave
Normal Conduction
- Fast Pathway: Fast conduction, Long refractory time
- Slow Pathway: Slow conduction, Short refractory time
- Premature AP occurs behind normal conduction. When it reaches the end the fast pathway is not refractory thus in addition to normal distal wave the premature wave travels retrograde up the fast pathway generating a loop.

Normal Sinus Rhythm

Normal Sinus Rhythm
- Regular PP and RR intervals
- Rate of 60 to 100 beats per minute.
- PR of 0.12 to 0.20 sec
- QRS of 0.04 to 0.10 sec
- 0.2s/5 boxes means each small square = 0.04 sec

Heart Rate Calculation

We can calculate the beats per minute (bpm) by dividing 1500 by the number of SMALL squares between two R waves (R-R interval = one beat)
- Heart Rate (bpm) = \frac{1500}{\text{# of boxes from R to R}}
- Each small square = 0.04 sec

Heart Rate

Normal heart rate between 60-100 bpm
A general quick assessment of HR can be completed by looking at the large squares!
# of Large Boxes: Heart Rate:
- 1
- 2
- 3
- 4
- 5
- 6

Sinus Tachycardia

Sinus Tachycardia- SA node depolarization rate is abnormally fast (usually greater than 100 beats/min) due to increased automaticity
- Causes: increased sympathetic or decreased parasympathetic activity, low blood pressure and hypoxia
- Physiology consideration:
  - Can be normal in exercising or periods of stress etc.
  - With other underlying disease it is a sign of stress on heart and increase O2 need
  - Ventricles may not have enough time to fill (decreased diastolic filling) leading to decreased SV and CO
- HR = \frac{1500}{\text{# blocks R to R}}
  - OR 2 large blocks ~ 150bpm
  - $\frac{1500}{10} = 150 \text{ bpm}$

Sinus Bradycardia

Sinus Bradycardia- SA node depolarization rate is abnormally slow (usually below 60 beats/min)
- Causes and Physiology consideration:
  - Can be normal (during sleep and well-trained individuals) if bodies O2 demands are met no treatment needed
  - Abnormal causes may include myocardial ischemia/infarction, side effect of drugs, hyperkalemia
  - May lead to decreased CO
- HR = \frac{1500}{\text{# blocks R to R}}
  - OR 8 large blocks ~ 30 bpm
  - $\frac{1500}{42} = 35 \text{ bpm}$

Sinus Arrhythmia

Sinus Arrhythmia- Slight irregular rhythm
- Causes and Physiology consideration:
  - A degree of sinus dysrhythmia is a normal finding in most cases due to variation in heart rate caused by respiration.
  - CO maintained à No treatment required
  - In older individuals it is not normal and may indicate myocardial ischemia (affecting SA node), sinus node dysfunction or side effect of drug treatments.

Sinus Arrest or Sinus Pause

Sinus Arrest (Pause): SA node fails to fire (Asystole)
- Many causes: some include myocardial infarction, electrical shock, electrolyte imbalances, acidosis and extreme parasympathetic activation
- Physiology consideration:
  - Sinus arrest is when the sinus fails to fire, in this case the AV node or other myocardial cell can take over. If this is brief (less than 3 seconds), then no treatment needed, if longer may need artificial pacemaker
  - Asystole is when there is no Pacemaker Function à Flat ECG à NO CO (this is an example of when individuals code) and may result in death
- Escape rhythm from other cells can be slower, resulting in non normal rhythm

Premature Atrial Complex (PAC) and Tachycardia

Identifiers
- Rhythm: Irregular (early)
- P-wave: Premature (abnormal) or hidden
- PR Interval: Normal
- QRS: Normal
- P wave is abnormally shaped, but normal QRS follows
- Not clinically significant if isolated
Premature Atrial Complex (PAC): Ectopic pacemaking tissue within atria
- Causes: Hypertension, ischemia, cardiomyopathy, alcohol/drugs, inherited conduction abnormalities
- Physiology consideration:
  - Common among healthy individuals and those with heart disease
  - Premature atrial contraction means chamber may not have filled completely. Only treated if individual is symptomatic (tachycardic)

Atrial Flutter

Identifiers
- Rhythm and Heart Rate: Regular or Irregular, 240-350 bpm
- P-wave: Absent, sawtooth flutter waves
- PR Interval: N/A
- QRS: Normal
- Ratio of Atrial:Ventricle Contractions Matter!
  - If 1:1 with atria contracting at 300bpm then ventricles also at 300 bpm, rapid ventricle contraction, resulting in low CO
  - If 4:1 with atrial at 300bpm then ventricles are at 75 bpm, result is a slower ventricle contraction rate
Atrial Flutter: Atria contract abnormally fast (240-350 beats/min)
- Causes: Hypertension, ischemia, cardiomyopathy, alcohol/drugs, inherited conduction abnormalities
- Physiology consideration:
  - Faster atrial contractions mean the atria is not moving blood to ventricles as effectively which may lead to reduced CO
  - Slow moving blood may lead to stagnate blood and thrombus risk

Atrial Fibrillation

Identifiers
- Rhythm and Heart Rate: Irregular, variable rate
- P-wave: Absent, quiver waves
- PR Interval: N/A
- QRS: Normal
Atrial Fibrillation: Uncoordinated irregular atrial contraction accompany irregular ventricle rhythm and rate
- Causes: Hypertension, ischemia, cardiomyopathy, alcohol/drugs, inherited conduction abnormalities
- Physiology consideration:
  - Fibrillation (quivering) of atria occurs instead of contraction allowing atrial blood to stagnate—can lead to thrombus formation
  - Irregular ventricle activity results in reduced CO
- Atrial impulses appear as small, squiggly waves of various sizes and shapes à “quiver” rather than contract
- Most atrial depolarizations are blocked at the AV node. Only some get through

Premature Ventricular Complex (PVC)

Identifiers
- Rhythm and Heart Rate: Normal
- P-wave: No P Wave corresponding to QRS
- PR Interval: Normal
- QRS: Wide, abnormal shape
- Next sinus discharge does not produce a QRS, so a beat is skipped.
Premature Ventricular Complex: Ventricles spontaneously depolarize
- Causes: Drugs, electrolyte imbalance, ischemia, increased sympathetic activity, triggered activity, reentry
- Physiology consideration:
  - Usually spontaneous and do not require treatment
  - Longer pauses between ventricular contraction can lead to more filling and strong contractions, felt as a palpitation
  - Can be clinically concerning depending on risk factors

Ventricular Tachycardia

Identifiers
- Rhythm and Heart Rate: Usually Regular, 100-200
- P-wave: Very difficult to detect
- PR Interval: Very irregular, if P waves are seen
- QRS: Wide, bizarre, abnormal shape
- May be fatal without immediate treatment if sustained
Ventricular Tachycardia: 3 or more PVCs at a rate of 100 beats/min
- Patient might have HR of up to 250 bpm!
- Causes: Stimulants, electrolyte imbalances, MIs, ischemia
- Physiology consideration: Beating so fast chambers cannot fill with blood resulting in reduced CO that does not meet bodies demands

Ventricular Fibrillation

Identifiers
- Rhythm and Heart Rate: Irregular
- P-wave: Absent
- PR Interval: N/A
- QRS: No QRS- Fibrillatory baseline
- Ventricles quiver rather than contract.
- No pulse, unconsciousness, death in minutes if not reversed.
- CPR needed.
Ventricular Fibrillation: Rapid, uncoordinated cardiac rhythms that result in quivering and reduce contraction effectivity
- Causes: Not always clear. Medications, drugs, electrolyte imbalances and ischemia. Stress or damage causes structural or electrical changes myocardiocytes syncytium
- Physiology consideration: Quivering is not a strong ventricular contraction leading to reduced CO

First Degree AV Block

Identifiers
- Rhythm and Heart Rate: Regular
- P-wave: Each P is associated with QRS
- PR Interval: Prolonged >0.20 sec
- QRS: Normal
- Rarely Treated
First Degree AV Block: signal moving from atria to ventricles is delayed but still makes it to the ventricles
- Causes: Hypertension, MIs, drugs, congenital heart defect
- Physiology consideration: Asymptomatic as the contraction still occurs

Second Degree AV Block, Type I (Mobitz type I or Wenckebach)

The PP intervals are constant, whereas the RR intervals vary
Causes: Typically due to reversible ischemia of the AV node, associated with acute MI
Physiology consideration: Asymptotic usually but can cause lightheadedness, dizziness, etc. due to decreased ventricle contraction leading to decreased CO
Second Degree Block- some atrial impulses do not conduct to ventricles
- 2 Types:
  - Second Degree Block- Type I- progressively lengthening PR intervals due to AV delay until one P wave is not conducted (dropped beat or a beat is skipped) and ventricles do not contract

Second Degree AV Block, Type II (Mobitz type II)

Lone P waves
In this strip every third P wave is conducted
Causes: Mis, cardiomyopathies, hyperkalemia
Physiology consideration:
- Symptoms vary depending on number of dropped beats.
- May also result in severe bradycardia depending on the number of dropped beats
- May progress to third degree
Second Degree Block- some atrial impulses do not conduct to ventricles
- 2 Types:
  - Second Degree Block- Type II- no lengthening of PR interval with presence of non- conducted P waves (dropped beats)

Third Degree (Complete) AV Block

Third Degree Block- No conduction between atria and ventricles
- Physiology consideration: Atria will contract normal, but ventricles are not being conducted (though may have some escape beats) resulting in reduced CO due to ventricles lowered conduction rate
Identifiers
- Rhythm and Heart Rate: Irregular
- P-wave: Independent of QRS
- PR Interval: Unequal
- QRS: narrow or wide (depending on where block is)
- Severity of symptoms is determined primarily by the heart rate, with slower rhythms being more serious
- Pacemaker required

First Degree AV Block

Saying: If the R is far from the P, then you have a FIRST DEGREE!
Remember:
- Prolonged PR interval (>.20 sec)
- Each P wave is associated with a QRS.
- Common during infection. Rarely treated

Second Degree AV Block

Saying: If some Ps don’t get through, then you have Mobitz 2
Remember:
- Constant PR interval
- Lone P waves
- In this strip every third P wave is conducted.
- Bradycardia is present. May progress to third degree.
Saying: Longer, longer, longer, drop! Then you have a Wenckbach
Remember:
- Lengthening PR interval until one P wave is not conducted. A beat is skipped.
- Cycle repeats

Third Degree AV Block

Saying: If Ps and Qs don’t agree, then you have a THIRD DEGREE
Remember:
- P waves are independent of QRS. Unequal PR intervals
- QRS is narrow or wide.
- No electrical connection between atria and ventricles.
- Constant PP and RR intervals
- Bradycardia is present. Pacemaker required.

Dysrhythmias Treatments

Drugs
- Alter movement of ions across cardiac cell membranes
Pacemakers (stimulate the SA node)
Ablation procedures (radiowave ablation)
Cardioversion- impulse is synchronized to the R wave, 10-100 J delivered
- Only used on dysrhythmias that have a QRS!
Defibrillation- impulse is not synchronized to the R wave, 200-350 J delivered
- Implantable defibrillators
- Used when there is NOT an R wave