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Definition:
- Arrhythmia means without rhythm.
- Dysrhythmia (bad rhythm) = Arrhythmia.

Examples of arrhythmias include:
  - Premature Beats
  - Paroxysmal Tachycardia
  - Supraventricular Arrhythmias
  - Ventricular Arrhythmias

Definition:
  - Premature beats interrupt the underlying rhythm by occurring earlier than expected.
  - Types of premature beats include:
    1. PACs (Premature Atrial Contractions)
    2. PJCs (Premature Junctional Contractions)
    3. PVCs (Premature Ventricular Contractions)

Characteristics:
- Early beat arises from an area in the atria other than the SA node, resulting in a different shape P Wave.
- The impulse is conducted with a narrow QRS complex followed by a pause.
Etiologies:
  - Increased sympathetic input,
  - Exogenous stimulants,
  - Drug interactions,
  - Acute Myocardial Infarction (AMI),
  - Cardiac ischemia,
  - Idiopathic causes.

Characteristics:
- Early beat arises from the AV node or junction.
- Generally, the impulse is conducted with a narrow QRS complex.
Common Etiologies:
  - Ischemia,
  - Hypoxemia,
  - Valvular disease,
  - Digitalis toxicity or normal variant.

Characteristics:
  - Early beat arises from the ventricles, resulting in widened QRS complexes (>0.12 seconds).
  - PVCs appear very different from normal sinus-conducted beats.
  - PVCs can occur in:
    - Isolated complexes,
    - Pairs,
    - Triplets,
    - Repeating sequences.
Clinical Significance:
  - If greater than 6 PVCs per minute, suggests pathology.
  - Three or more PVCs in a row is a run of Ventricular Tachycardia (VT).
  - Sustained VT is defined as lasting more than 30 seconds.

PAC:
- Followed by an incomplete compensatory pause because it resets the sinus node timing, causing the following P Wave to occur earlier than expected.
PVC:
- Followed by a complete compensatory pause due to the inability of the sinus P Wave to reach the ventricles which remain refractory from the PVC.

Couplets:
- Two PVCs in a row.
Triplets:
- Three PVCs in a row.
Bigeminy PVCs:
- Occurrence where each normal complex is followed by a PVC, forming groups of two (normal QRS followed by PVC).
Trigeminy and Quadrigeminy PVCs:
- Trigeminy: PVC every third beat.
- Quadrigeminy: PVC every fourth beat.
Clinical Implication:
- Increased frequency of PVCs in patients with heart disease predicts ventricular fibrillation and sudden death.
Causes of PVCs:
  - Electrolyte imbalance,
  - Hypoxia,
  - Ischemia,
  - Acute Myocardial Infarction,
  - Medication toxicity.

Definition:
- A ventricular extrasystole caused by ventricular depolarization occurring superimposed on the previous beat's repolarization, due to premature ventricular complex near the peak of the T wave.
Significance:
- PVCs can occur early (R-on-T), after the T wave, or late - often fusing with the next QRS (fusion beat).
- R-on-T PVCs are particularly dangerous in acute ischemic situations, increasing vulnerability to ventricular tachycardia or fibrillation.

Four Mechanisms:
  1. Reentry (most common)
  2. Automaticity: Ectopic foci become potential pacemakers, also known as automaticity foci (located in atria, AV Node, Purkinje system, and ventricles).
  3. Triggered Activity
  4. Parasystole

Definition:
- A reentrant circuit, or accessory pathway, causing premature heartbeats. Often likened to a dog chasing its tail or a race track scar where tissue does not conduct properly.
Episodes typically start and end suddenly.

Characteristics:
- Fast pathway conducts quickly; takes longer to recover.
- Slow pathway conducts slowly; has a shorter recovery time.
Mechanism: PAC blocks in the fast pathway, conducts down the slow pathway, and retrograde through the fast pathway.
Process:
  1. PAC enters slow pathway; blocked in fast pathway.
  2. Impulse conducts anterogradely through slow pathway.
  3. Ventricles activated synchronously.
  4. Impulse activates atria retrogradely, reenters slow pathway.

Conditions associated with re-entry include:
  - Ventricular tachycardia,
  - Atrial SVT,
  - Atrial re-entry conditions such as atrial tachycardia, atrial fibrillation, and atrial flutter.
Associated Conditions:
- WPW (Wolff-Parkinson-White syndrome)
- SA node disease related to reentry circuits.

Definition:
- Begins abruptly and ends suddenly. Characterized by a high rate of atrial activation (between 160-220 beats/min) resulting from a reentrant activation front in the atria.
In ECG, the P-wave is usually regularly followed by a QRS complex.
Mechanisms:
1. Re-entry (loop of electrical current)
2. Automaticity (ectopic)
Causes:
  - Anxiety,
  - Stimulants (e.g., epinephrine),
  - Hypoxia,
  - Overactive thyroid,
  - In women, onset of menstruation.

Definition:
- An ectopic focus from the atrium creates a P-wave different from previous ECG readings, indicating a source outside the SA node. Paroxysmal refers to sudden, unpredictable outbursts.

Characteristics:
  - Results from fast and slow pathways in the AV junction causing a reentrant rhythm at rates > 150 BPM.
  - Impulses stimulate the ventricles using the normal conduction pathway, resulting in a normal QRS complex.
  - Ventricular rate typically between 150-250 BPM with normal QRS and regular R-R intervals.
  - P-waves may be inverted or buried within the QRS complex.