Sinus Bradycardia

What is Sinus Bradycardia?

Sinus bradycardia is a condition that slows down your heart rate. Patients with the condition have a sinus rhythm with a heart rate of fewer than 60 beats per minute or less, when at rest. A slow heart rate at the time of rest is actually normal, but when your heart beat goes less than 60 beats per minutes, it is abnormal.

The condition becomes symptomatic when the rest rate goes below 50 beats a minute, therefore, it is good practice to monitor your heart. This is to some people more necessary than with others because factors like taking good medications for physical fitness predispose you to the risk of sinus bradycardia.

In an adult, the normal heart rate at rest is between 60 and 100 beats a minute. If the condition affects the circulation of oxygen to the body controlled by the pumping action of the heart, then it can be a serious problem to the individual. Understanding how the heart works will form the basis to concepts like treating and managing the condition. ^{3,4, 8, 9}

How the Heart Works?

The heart’s function is to circulate blood through the body by an electric pumping action that takes place in two stages. Generation of heartbeats is basically the result of electric signals coordinated to imitate the action of a pump. The right-hand side chamber also called atrium initiates this process.

The heart is a four-chambered muscular organ the size of your fist. The chambers: right; left atria, and right; left ventricles. The right side pumps blood to the lungs while the left pumps to the rest of the body.

In the right atrium, there are special cells called the sinoatrial node (SA node), which trigger the generation of the initial electric impulse. They also act as an automatic pacemaker by carrying that initial electric impulse along the heart’s muscle imitating an electric wiring.

The signal causes the muscle cells on both the right and left atria to contract simultaneously coordinating the squeeze so thus prompting the heart to beat in a steady rhythm. Heart beats describe the blood pumping action of the heart that enables its circulation throughout the body.

Blood circulating on the right side comes from the body with depleted oxygen, therefore, it is pumped to the lungs to get oxygen and release carbon dioxide. Consequently, the oxygenated blood returns to the left side and pushed by the more muscular left ventricle to the entire body.

Its movement from the right atrium to the right ventricle through to the lungs and then to the left atrium and left ventricle before finally circulating to the body is a result of the traveling electric impulses.

As the electric impulses travel across the atria, they contract to push the blood to the ventricles. These impulses then collect in the His bundle cells making up the atrioventricular node, which transmits the signal. The His cells are a bunch of specialized cells that transmit the signal down branches within ventricles.

As a result, the ventricles also contract and these combined contracting actions cause blood to flow like in a pump fashion observed as heart beats.

However, when the pulses do not fire off when they should, abnormal heartbeats are observed, a condition called arrhythmias. In bradycardia, the generation of the electric signal is slowed or blocked thus slowing down the time between consecutive heartbeats.

If the electric activity is working normally, but slower than in most people, you will not be diagnosed with sinus bradycardia. Your heart rate, however, is slower than normal without the symptoms associated with the condition. Other conditions may cause the heart to flutter or beat too fast. ^{1, 2, 3}

Causes

Problems that affect the sinus node may cause sinus bradycardia, therefore, the condition often begins in the sinoatrial node. As a result, the sinoatrial node may:

Misfire failing to discharge at a regular rate
Wear out or in the cause of time, slow down discharging the impulses as at a reduced rate
Discharge an electric impulse, which is blocked before the atria can contract.
The discharged signals may get transmitted to the atria, but blocked from traveling to the ventricles referred to as an atrioventricular or heart block.

There are various levels or degrees of heart blocks, and they include:

First degree

All the signals from the atria get to the ventricles but in a slower than normal time.

Second degree

Not all signals from the atria reach the ventricles resulting in a slower or irregular rhythm.

Third degree

None of the signals from the atria reach the ventricles causing the His cells and other tissues in the ventricles to function as their pacemaker. The substitution slows down the pumping in these chambers resulting in a slower beat of the ventricles.

Bundle branch block

The electric signal is interrupted somewhere in the right or left ventricular branches close to the end of their path.

The following are the underlying causes for which the SA is affected or becomes problematic:

Heart tissue damage observed in aging, heart disease, or after an episode of heart attack
Hypertension
Congenital heart defects
Myocarditis, which is the infection of the heart tissue
Complications after heart surgery
Electrolytes imbalance necessary in conducting the electric impulses
Repeatedly disrupted breathing when sleeping called obstructive sleep apnea
Conditions like hypothyroidism, lupus, and rheumatic fever
Hemochromatosis- where iron buildups in organs including the heart
Medications that are given for other heart rhythm disorders, hypertension, and psychosis.

Risk factors

Since sinus bradycardia is associated with heart diseases, factors that increase your risk of heart disease also increase the chances of suffering from this condition. These risk factors for heart disease include:

Smoking
High blood pressure
Uncontrolled drinking of alcohol
Using recreational drugs
Anxiety or psychological stress
Practices related to good physical fitness.

Symptoms

Fatigue and tiring rapidly after exertion
Dizziness
Weakness
Fainting that may be triggered by choking in some cases. A well-known case of this is when former president George Bush fainted after a choking episode. This type of fainting is medically known referred to as the vagus nerve reflex.
Shortness of breath
Confusion
Memory problems
Chest pains
Heart failure in severe cases where the heart is unable to pump enough blood
Sudden cardiac arrest or even death.

Diagnosis

Diagnosis involves evaluating symptoms and reviewing the patient’s history including past medical conditions in their family.

An electrocardiogram or ECG is used in the primary evaluation of the condition. It uses small sensors attached to your chest, which record the electric signals path in your heart. The patterns are then monitored to determine what kind of bradycardia you are suffering from. ECG devices include:

Holter monitor

A portable device designed to record your heart’s activity through a 24-hour period.

Event recorder

Designed to monitor your heart’s activity during the period when the symptoms are manifesting.
Tilt table test – an ECG monitors your heart rate as you lie on a table tilted to imitate the standing position.
Exercise test- In this test, your doctor uses an ECG to monitor your heart as you take exercise to increase physical activity.
Other tests- If sleep apnea is suspected, tests thatmonitor your sleeping patterns are used.
Laboratory tests- Blood tests to detect other underlying conditions that may be causing the sinus bradycardia.

Treatment

The condition can be normal in athletes and young healthy people resulting in no symptoms. Some other cases require treatment, especially when it becomes symptomatic. Treatment may involve:

Treating the underlying condition

Correcting the condition that is causing it relieves the bradycardia.

Changing medication

Alternative medicines to replace those that are causing the bradycardia should correct the condition. If there are no alternatives, a pacemaker is necessary.

Pacemaker

This is a device implanted under the collarbone to simulate the action of a normal SA. It is operated by batteries to provide the electricity and wires travel from the device through the veins and in to your heart.

Sensory electrodes are attached at the end of the wires to the tissues of the heart. These electrodes monitor your heart’s electrical activity and send energy in form of pulses to maintain a normal heart rate.

Prevention

Treating heart disease and avoiding risk factors associated with heart disease can eliminate the risk of suffering from this condition. Lifestyle practices that achieve this include:

Exercise and a healthy diet: eat meals that are low in fats and rich in fiber like whole grains and vegetables. Regular exercising is also important.
Maintaining a healthy weight: weight disorders cause heart disease
Control and consciously monitor factors that elevate your blood pressure and cholesterol levels.
Avoid smoking, excessive drinking and using recreational drugs
Control factors that predispose you to stress and anxiety.
If you have a heart condition, do not fail to attend a scheduled check up.

Reference List

Heart rhythm disorders. Available at http://www.medicinenet.com/heart_rhythm_disorders/article.htm
Causes of bradycardia. Available at http://www.mayoclinic.org/diseases-conditions/bradycardia/basics/causes/con-20028373
Bradycardia. Available at http://www.webmd.com/heart-disease/bradycardia#1
Bradycardia. Available at http://www.mayoclinic.org/diseases-conditions/bradycardia/basics/definition/CON-20028373?p=1
Causes of sinus bradycardia. Available at https://www.reference.com/health/causes-sinus-bradycardia-f65cd8dfb4456f68?qo=cdpArticles
Treating bradycardia. Available at https://www.reference.com/health/treatment-bradycardia-ba573836c1ed6f6d?qo=contentSimilarQuestions
Symptoms of bradycardia. Available at https://www.reference.com/health/symptoms-bradycardia-5503f402a5b1514b?qo=cdpArticles
Sinus bradycardia. Available at https://www.reference.com/health/sinus-bradycardia-93eae04c88b56ca1?qo=cdpArticles
Sinus bradycardia. Available at http://emedicine.medscape.com/article/760220-overview
Sinus Bradycardia- Diagnosis. Available at http://www.mayoclinic.org/diseases-conditions/bradycardia/basics/tests-diagnosis/con-20028373