Nomotopic arrhythmias (sinus tachycardia, sinus bradycardia, sinus arrhythmia) – etiology, pathogenesis, and clinical manifestations.
Nomotopic arrhythmias (also called sinus arrhythmias ) are rhythm disturbances originating from the sinoatrial (SA) node, which remains the dominant pacemaker.
Types
1 Sinus tachycardia
Etiology
Physiological:
- Exercise.
- Fever.
- Pain.
- Anxiety, excitement.
Pathological:
- Hyperthyroidism.
- Hypovolemia (shock, dehydration).
- Heart failure.
- Anemia.
- Pulmonary embolism.
- Drugs (catecholamines, atropine).
Pathogenesis
Increased sympathetic tone or decreased vagal (parasympathetic) activity → increased SA node automaticity → faster discharge rate.
Clinical manifestations
Often asymptomatic if mild.
Palpitations.
Dyspnea on exertion.
Dizziness (rare).
Exacerbation of angina in coronary artery disease.
2 Sinus bradycardia
Etiology
Physiological:
- Well- trained athletes.
- Sleep (increased vagal tone).
Pathological:
- Hypothyroidism.
- Hypothermia.
- Increased intracranial pressure (Cushing reflex).
- Myocardial infarction (especially inferior MI involving the SA node).
- Sick sinus syndrome.
- Drugs (beta- blockers, digoxin, calcium channel blockers).
Pathogenesis
Increased vagal tone or decreased sympathetic activity → reduced automaticity of the SA node → slower discharge rate.
Clinical manifestations
May be asymptomatic if mild.
Fatigue, weakness.
Lightheadedness or dizziness.
Syncope (if severe).
Exercise intolerance.
3 Sinus arrhythmia (respiratory sinus arrhythmia)
Etiology
Commonly seen in healthy young individuals.
Related to breathing (physiological).
Pathogenesi s
During inspiration, vagal tone decreases → heart rate increases.
During expiration, vagal tone increases → heart rate decreases.
Represents normal modulation of the SA node by the autonomic nervous system.
Clinical manifestations
Usually asymptomatic.
No clinical significance; considered a normal variant.