Cardiac Dysrhythmia Study Notes

Electrical Properties of the Heart

• Automaticity: depolarize spontaneously (SA node, AV node, His bundle, Purkinje fibers).

• Excitability: depolarize in response to stimulus.

• Conductivity: transmit impulses through conduction pathways.

• Contractility: shorten fibers, generate pressure, pump blood.

Nervous System Influence

• Sympathetic: ↑ HR & conduction (atria + ventricles).

• Parasympathetic: ↓ HR, conduction, irritability (atria only).

Conduction System Rates

• SA node: 60–100 bpm

• AV node: 40–60 bpm

• Ventricles: 20–40 bpm

EKG Basics

• P wave: atrial depolarization

• QRS complex: ventricular depolarization

• T wave: ventricular repolarization

• U wave: final ventricular repolarization

• PR interval: 0.12–0.20 sec (~4 small boxes)

• QRS duration: 0.06–0.10 sec (~2 small boxes)

• QT interval: QRS onset → T wave return

Normal Sinus Rhythm (NSR):

• Rate: 60–100 bpm

• Regular rhythm

• Normal P, PR, QRS

• Significance: optimal cardiac output

Sinus Rhythms

Sinus Bradycardia (<60 bpm)

• Causes: athletes, sleep, vagal tone, digoxin, beta-blockers, morphine, hyperkalemia, ischemia.

• Effects: ↓ CO → hypotension, dizziness, syncope.

• Tx:

  • Asymptomatic → observe

  • Symptomatic → treat cause, atropine, pacing

Sinus Tachycardia (100–150 bpm)

• Causes: exercise, hypovolemia, hypoxia, hyperthyroidism, anemia, pain, fever, CHF, stress.

• Effects: ↑ O₂ demand → angina, MI, pump failure.

• Tx: only if symptomatic; treat cause (O₂, fluids, meds).

Sinus Arrest / Pause

• Cause: SA node failure (MI, disease).

• Effect: ↓ CO.

Sick Sinus Syndrome

• Alternating bradycardia & tachycardia.

• Common in elderly/diseased heart.

• Tx: pacemaker, meds.

Atrial Arrhythmias

PACs (Premature Atrial Contractions)

• Early, abnormal P waves.

• Causes: stress, stimulants, hypoxia, electrolyte imbalance.

• Effect: usually benign; frequent PACs ↓ CO.

Atrial Tachycardia (AT) / Supraventricular Tachycardia (SVT)

• Rate: 150–250 bpm.

• Effect: ↓ CO, ↑ O₂ demand.

• Tx: treat cause, vagal maneuvers, meds.

Atrial Flutter

• Rate: 250–350 (sawtooth pattern).

• Effect: ↓ CO; may progress to Afib; risk CHF/ischemia.

Atrial Fibrillation (AFib)

• Chaotic atrial activity (350–700 bpm), irregularly irregular.

• Causes: CHF, hypoxia, post-surgery, valvular disease.

• Effects: ↓ CO (loss of atrial kick), clot risk, ↑ O₂ demand.

Ventricular Arrhythmias

PVCs (Premature Ventricular Contractions)

• Wide, bizarre QRS >0.12 sec.

• Types: unifocal, multifocal, couplets, bigeminy, trigeminy, R-on-T.

• Causes: stimulants, hypoxia, hypokalemia, MI, dig toxicity.

• Effects: may progress to VT/VF.

• Tx: treat cause, amiodarone.

Ventricular Tachycardia (VT)

• Rate: 100–250 bpm; ≥3 PVCs in a row.

• Types: monomorphic, polymorphic, torsades de pointes.

• Effect: severe ↓ CO; often → VF; life-threatening.

Ventricular Fibrillation (VFib)

• Chaotic rhythm, no CO.

• Effect: fatal if untreated.

• Tx: defibrillation (shock).

Asystole

• Flatline; no electrical activity.

• Effect: no CO, poor prognosis.

• Tx: CPR, epinephrine, treat reversible causes.

AV Blocks

1st Degree AV Block

• PR >0.20 sec, all beats conducted.

• Usually benign → monitor.

2nd Degree Type I (Wenckebach)

• PR lengthens → dropped QRS.

• Often drug/MI related.

• Usually benign unless symptomatic.

2nd Degree Type II

• Sudden dropped QRS; PR constant.

• High risk → 3rd degree block/asystole.

• Tx: pacing.

3rd Degree (Complete Heart Block)

• Atria & ventricles beat independently.

• Ventricular escape rhythm (20–40 bpm).

• Effects: severe ↓ CO; risk asystole.

• Tx: pacemaker.