Final answer:
When faced with marked sinus bradycardia, look for symptoms indicating insufficient oxygenated blood delivery, explore potential intrinsic or extrinsic causes, and determine the appropriate treatment based on the underlying cause.
Step-by-step explanation:
If a patient has marked sinus bradycardia, which is a resting heart rate below 60 beats per minute (bpm), it is important to look for symptoms that may indicate the heart is not supplying enough oxygenated blood to the tissues. Symptoms to watch for include weakness, fatigue, dizziness, fainting, chest discomfort, palpitations, or respiratory distress. While a heart rate above 50 bpm is usually not clinically significant provided that the patient is asymptomatic, the presence of such symptoms could warrant further investigation.
Causes of sinus bradycardia can be inherent, such as abnormalities in the sinoatrial (SA) or atrioventricular (AV) nodes, or external, such as metabolic disorders, endocrine pathologies involving the thyroid, electrolyte imbalances, neurological disorders, autoimmune diseases, effects of drugs like beta blockers, recreational drug use, and prolonged bed rest. Establishing the underlying cause is critical for treatment, which may include interventions like a pacemaker and supplemental oxygen.