A heart rate slower than normal is often encountered among various demographics. Referred to as sinus bradycardia, the condition is characterized by a heartbeat of less than 60 beats per minute originating from the sinus node — a small mass of tissue that produces electrical impulses or stimuli; it’s also known as the natural pacemaker of the heart. The condition is often considered a sign of ideal heart health for athletes. However, for those not engaged in regular, intense workouts, it can arise due to underlying issues such as age, inflammatory problems or faulty electrical conduction in the heart.
Sinus bradycardia: What are its causes?
The main factors that give rise to a slow heart rate include:
♦ Sick sinus syndrome
Sick sinus syndrome (SSS) is a heart rhythm disorder resulting from dysfunction of the sinus node, which is responsible for regulating heart rate. From age and genetic factors to damaged heart tissues, the reasons for this condition can be many. “If left untreated, sick sinus syndrome can progress to heart blocks, disrupting the normal flow of impulses,” says Dr Varun Bansal, consultant, cardiology and cardiothoracic surgery, Indraprastha Apollo Hospital, Delhi.
♦ Thyroid hormone deficiency
Dr K U Natarajan, professor & head, cardiology, Amrita Hospital, Kochi, says hypothyroidism or thyroid hormone deficiency can contribute to a slow heart rate by reducing metabolic activity, diminishing sympathetic nervous system influence, altering the sensitivity of the heart muscles and causing electrolyte imbalances.
♦ Medication
“Beta blockers are prescribed for hypertension, angina (chest pain), heart failure, heart attack recovery, etc.,” says Dr Natarajan. They work by blocking the effects of adrenaline (a stress hormone), reducing heart rate and blood pressure.
In the case of sinus bradycardia, beta blockers can slow down the heart rate by inhibiting the action of the sympathetic nervous system, specifically the beta receptors that normally stimulate the heart to beat faster.
♦ Aging
Sinus bradycardia is not exclusive to athletes; elderly individuals may also experience a natural decline in heart rate. However, any sudden or severe onset of bradycardia in older adults should be addressed at the earliest.
When is a slow heart rate healthy?
Sportspersons and other endurance athletes may showcase sinus bradycardia without any underlying health issues. “Athletes who regularly exercise can have a resting heart rate of 50 beats per minute. This does not mean that the person has a problem; on the contrary, it is a sign of good heart health,” says Dr Natarajan.
High-intensity workouts can thicken the heart muscles, especially in athletes and those who regularly lift weights in the gym. Referred to as an athlete’s heart, it’s the natural adaptation of the cardiac muscles to meet the physical demands of intense exercise and training. They may have a resting heart rate of 50 beats per minute, which is often a sign of excellent cardiovascular health, reflecting the heart’s efficiency in pumping blood.
Symptoms of sinus bradycardia
Some characteristic manifestations of sinus bradycardia include:
♦ Dizziness
“People with a low heart rate usually do not show any symptoms; however, if it goes below 50 or 48 beats per minute, they may feel weakness and dizziness due to low cardiac output,” says Dr Bansal. Insufficient blood supply to the brain can even cause one to faint.
♦ Exercise intolerance
Exertion increases one’s heart rate, which helps them perform intense exercises. “However, if someone has a very low heart rate, which doesn’t increase even after exercising, they will get extremely tired. This is known as exercise intolerance,” shares Dr Natarajan. They may also feel breathless and less energetic.
♦ Temporary loss of consciousness
Those with severe bradycardia, having a resting heart rate of 30 beats per minute, can suddenly black out. Additionally, if the gap between heartbeats is very slow or the individual does not have a pulse for more than three seconds, they can temporarily lose consciousness as well.
Diagnosing sinus bradycardia
The primary techniques used to diagnose sinus bradycardia include:
♦ ECG
Dr Bansal says if one’s heart rate is abnormally low, the doctor will start with a baseline ECG (electrocardiogram). This helps measure their pulse rate, which can confirm the diagnosis.
♦ Holter monitoring
In this case, a Holter monitor — a wearable device that records the heart’s rhythm and electrical activity over 24 hours or longer — is used to detect any irregularities in heart rate. “Apart from showing one’s accurate heart rate, the device can also detect if it increases during everyday activities like walking,” says Dr Natarajan.
♦ Echocardiogram
An echocardiogram utilizes sound waves to create a detailed image of the heart’s structure and function.
♦ Treadmill test
Doctors may also recommend a treadmill test to assess if the heart responds appropriately to exercise. This helps determine if exercise intolerance is present.
In cases where sinus bradycardia leads to severe symptoms or complications, a pacemaker may be recommended, which helps regulate the heart’s rhythm by generating electrical impulses when needed.
Precautions to take
It’s crucial to be aware of the signs of bradycardia to prevent severe consequences. Those diagnosed with the condition should get screened for heart conditions on a regular basis. “If one has an episode of collapse, a cardiologist should be consulted immediately, as they might need a pacemaker,” cautions Dr Bansal.
One can also check their pulse using a pulse oximeter. “If it is consistently less than 60 beats per minute, one must seek medical help,” informs Dr Natarajan.
Takeaways
- Sinus bradycardia is a heart rhythm disorder characterized by a slow heart rate originating from the sinus node.
- It can be caused by aging, certain medications or conditions like sick sinus syndrome and hypothyroidism. The primary symptoms include dizziness, exercise intolerance and a temporary loss of consciousness.
- While a slower heart rate can be concerning for the general population, it can also be a sign of optimal heart health for endurance athletes and sportspersons.
- Being aware of the symptoms and regular monitoring of the pulse rate can help prevent severe consequences.
