What Medical Conditions Can Cause Low Heart Rate?
Bradycardia, or a low heart rate, is a condition of abnormal heart rhythm in which your heart beats lower than 60 beats per minute.
A lower-than-normal heart rate is common in athletes who have reduced body fat and strengthened the heart through aerobic exercise so much that it takes fewer beats to pump blood throughout the body. Sinus bradycardia is common among endurance athletes.
A low heart rate can present as fatigue, shortness of breath, lightheadedness, and weakness. Some people even faint as a result of a slow heart rate.
Bradycardia also occurs in healthy young adults and while sleeping. While a lower heart rate than usual is often not something to worry about or a medical emergency, it can be a warning sign for some individuals.
If caused by an underlying medical condition and experiencing the associated symptoms, seeking prompt medical attention is vital!
Multiple underlying health conditions can lead to a low heart rate. Some of the most common causes of bradycardia are mentioned below:
Infants may experience heart arrhythmias due to congenital heart disease (CHD). The prevalence of CHD was 6.9/ 1,000 live births in North America which makes it responsible for 1/ 3rd of all major congenital abnormalities.
These disorders are frequently associated with hampered electrical conduction of the heart that leads to bradyarrhythmias. Heart rate undulations are generally noted in infancy; however, they can arise at all ages.
Different treatment approaches to CHD include cardiac catheterization, fetal cardiac intervention, and heart surgery (transplant in severe cases).
The heart muscle has its own nerve supply, i.e., from the sinus and atrioventricular nodes. In a large number of cases, arrhythmias (atrial fibrillations) are linked to dysfunction of the sinus node.
Bradycardia can ensue if the electrical impulse from the sinus node to the atrioventricular node is blocked. Atrioventricular blocks are frequently associated with low heart rates.
Heart blocks are divided into three degrees. First-degree blocks are mild and rarely symptomatic. Second-degree blocks cause irregular rhythms and drops in beats, while there is no signal conduction to the ventricles in third-degree (complete) heart block.
In mild cases, lifestyle changes and medications can help manage the heart rate, but in severe cases, you will need to get an artificial pacemaker fit in your chest.
Another condition that can drop your heart rate to low levels is heart inflammation.
The heart muscle can become inflamed due to infections or autoimmune diseases. The condition is known as myocarditis. There can be inflammation of the outer heart layer (pericarditis), leading to bradycardia.
A 2018 study revealed a strong association between myocarditis in Chikungunya patients and bradycardia.
The study directs physicians in the US to check for the possibility of severe bradyarrhythmias in such patients.
Similarly, dengue fever can cause heart inflammation (peri and myocarditis), leading to significant sinus bradycardia. Management of infections can help correct the heartbeat rate.
Clinical cases of hypothyroidism typically show an unusually slow heart. Low levels of thyroid hormones (T3 and T4) from an underperforming thyroid gland push you into a low metabolic state.
Severe bradycardia and atrioventricular blocks are seen as secondary to hypothyroidism. Oral hormone supplementation and thyroxine hormone replacement therapy can successfully treat the condition.
There have been case reports of hypothyroidism and associated junctional bradycardia. New studies reveal that congenital hypothyroidism may also present as fetal bradycardia.
Rheumatic fever is an auto-immune inflammatory condition affecting the heart, joints, and brain. Young adults can suffer from complete heart blocks due to rheumatic fever. Thus, the disorder can directly cause bradycardia.
According to a case study in 2022, first-degree atrioventricular heart block is the most common heart disturbance reported in cases of acute rheumatic fever.
The study reported two cases of AV blocks with unstable bradycardia. The positive thing is that both cases completely recovered with the help of anti-inflammatory medications.
Another possible cause of sinus bradycardia can is electrolyte imbalance. You can enter a state of electrolyte imbalance due to dehydration, but cardiac manifestations are possible with the injudicious use of medications. Abrupt amounts of potassium and calcium can trigger a low heart rate.
According to a 2021 case report, a 59-year-old male patient diagnosed with COVID-19 presented with sinus bradycardia.
Investigations revealed inappropriate use of antidiuretic hormones that lead to electrolyte imbalance. That eventually leads to a low heart rate.
Certain medicines can lower your heart rate as a side effect. Drugs for managing heart rhythm disorder and hypertension (propranolol, verapamil, etc.) may also cause noticeable reductions in the heart beating rate.
Corticosteroid use can lead to sinus bradycardia. Lower-than-normal heart rate was seen in a young woman who was previously injected with 200mg of IV hydrocortisone. Heart rate normalizes after discontinuation of the high doses of the drug.
Other drugs that cause bradycardia as a side effect include:
- Mental health drugs
Many people experience abnormalities in the heart rhythm after a heart attack. Damage to the heart tissue (during a myocardial infarction) can lead to deviations in the heart rate. Low heart rate may also arise as a complication of heart surgery.
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