- Normal Cardiac Conduction:
- SA node: Initiates depolarization in the right atrium; influenced by sympathetic/parasympathetic systems.
- AV node: Located in the atrial septum; also influenced by autonomic nerves.
- Bundle of His: Divides into right/left branches, leading to Purkinje fibers; results in QRS wave on ECG.
- Bradycardia: Defined as heart rate <60 bpm.
- Sinus Node Dysfunction (SND): Slow SA node impulses.
- Atrioventricular Block (AV Block): Impaired impulse transmission from atria to ventricles.
- Sinus Node Dysfunction (SND):
- Symptoms: Weakness, palpitations, syncope.
- Causes: SA node or conduction pathway issues.
- Management: Correct underlying causes; pacing in severe cases.
- Atrioventricular Block:
- Types: First-degree (PR >200 ms), Second-degree (Mobitz I and II), and Third-degree.
- Management: Depends on severity; pacing may be required.
- Cardiac Implanted Devices:
- Permanent Pacing: Indicated for chronic bradycardia, AV block.
- Temporary Pacing: Used in acute, severe cases until permanent solution available.
- Pacing Modes: VVI(R), AAI(R), DDD(R), DDI(R), DOO/VOO; each with specific indications.
- Complications of Pacing:
- Undersensing: Failure to detect heart's own rhythm.
- Oversensing: Incorrect sensing of electrical signals.
- Failure to Capture: Inability to initiate heart muscle contraction.
- Fusion: Combination of pacemaker and intrinsic heartbeats.
- Diagnostic Approaches:
- ECG: Primary diagnostic tool.
- Imaging: Echocardiography, MRI, CT for structural assessment.
- Lab Tests: Electrolytes, thyroid function, infection markers.
- Therapeutic Approaches:
- Acute Management: Atropine, isoproterenol for symptomatic bradycardia.
- Chronic Management: Device implantation, medication adjustments.
- Special Considerations: Bradycardia post-heart surgery or TAVI.
- Key Practice Pearls:
- Accurate diagnosis: Differentiate between SND and AV block.
- Treatment tailored: Base on etiology and severity.
- Monitor implanted devices: Regular check-ups for function and battery life.