Heart sounds and atrial fibrillation: What they mean

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“Yes, it causes a classic irregular heart sound,” said Dr. Briana Costello, a cardiologist at The Texas Heart Institute Center for Cardiovascular Care. “However, some people either may not have it, or it may be impossible to detect with a stethoscope.”

To understand heart sounds, it helps to be familiar with basic heart structure and function.

How the heart works

The heart consists of two upper chambers, which are called the atria, and two lower chambers, which are called the ventricles.

Oxygen-poor blood flows into the right atrium and then moves into the right ventricle. The right ventricle pumps the blood into the pulmonary artery to the lungs, where it gets oxygen.

Next, oxygen-rich blood leaves the lungs through the pulmonary veins and enters the left atrium. Here, the heart pumps it into the left ventricle. The left ventricle then pumps oxygen-rich blood to the whole body.

What causes the four heart sounds?

Four valves in the heart open and close at specific times to control blood flow. These valves are responsible for the “S1 and S2 sounds.”

The heart has a beating phase called systole and a relaxed phase called diastole. Systole produces the S1 sound, which is the sound of the tricuspid valve and mitral valve closing. These valves sit between the right atrium and right ventricle and the left atrium and left ventricle, respectively.

Diastole produces the S2 sound, which is the sound of the pulmonary valve and aortic valve closing. The pulmonary valve is between the pulmonary artery and the right ventricle. The aortic valve divides the left ventricle and aorta, the main artery through which blood flow travels to all body parts.

Typically, heart sounds are called “lub dub,” with S1 causing the lub and S2 causing the dub. In people with a healthy heart, the intervals between S1 and S2 are regular.

In addition to S1 and S2, some people have S3 and S4 sounds.

The S3 sound is a low-frequency sound in early diastole. It may be a sign of conditions that involve higher left atrial volume and lower ventricular filling pressure.

Although S3 may be typical in children and adult athletes, it is also present in those with congestive heart failure. In heart failure, the heart cannot adequately pump blood to the body.

The S4 sound also occurs during diastole. It is the hallmark of conditions affecting ventricular function, such as a stiff left ventricle.

Dr. Costello explained that the irregular sound of the heart in atrial fibrillation has more to do with rhythm than a specific noise.

“The classic sound of this condition is not the pitch or the tone,” she said. “Instead, doctors listen to the cadence of the heartbeat. Generally, the heartbeat or rhythm sounds like a synchronized beating drum, but in atrial fibrillation, it is usually erratic, unorganized, and inconsistent in rhythm.”

“This irregular rhythm happens in the interval between S1 and S2,” Costello added. “If people with atrial fibrillation also have heart failure, it can cause the S3 sound, but they will not have the S4 sound.”

Atypical heart sounds are not always a sign of atrial fibrillation — they may be a sign of a different arrhythmia. “Other heart conditions that may contribute to abnormal sounds include benign heartbeats, premature atrial contractions, and more,” said Costello.

When a heart sound is benign, it means the atypical heartbeats are not a concern. A premature atrial contraction is one that occurs too early. When doctors detect atypical sounds, they may have to conduct additional testing to determine the specific cause. Although premature atrial contractions are typically benign, they can increase a person’s risk of developing atrial fibrillation.

They listen for heart sounds using a stethoscope, which amplifies noises that the heart and blood make. It consists of a headset with earpieces that tubing connects to a chest piece. The earpieces reduce the noise of the surroundings, which optimizes the ability of a doctor to hear the sounds. Doctors place the chest piece in different places to hear all four heart valves.

“After doctors pick up on an irregular heart rhythm with a stethoscope, they may follow up with an electrocardiogram, or EKG, which shows the heart’s electrical activity,” said Costello.

An EKG is the most common test for diagnosing an irregular rhythm. Additional tests may also be necessary, such as:

• blood tests to measure substances that may play a role in producing irregular heart sounds, such as thyroid hormones
• imaging tests to look at heart structure and function and evidence of scar tissue
• monitors for long-term recording of the heartbeat during a person’s everyday activities
• electrophysiology study, which provides additional information about heart electrical activity

“If someone has a heart murmur — which is an unusual sound between heartbeats — it may not necessarily lead to atrial fibrillation,” explained Costello. However, without treatment, some heart murmur causes can increase the risk of atrial fibrillation, she added.

“In other words, if an individual has irregular heart sounds but not atrial fibrillation, whether they eventually develop atrial fibrillation depends on the cause of the sounds,” said Costello. “It is worth noting that sometimes people naturally have extra heartbeats.”

Because atrial fibrillation can be life threatening, symptoms require medical attention. These include:

• a feeling that the heart is pounding or fluttering
• extreme tiredness
• lightheadedness
• shortness of breath
• chest pain

Someone with mild symptoms, such as fluttering, needs to make an appointment with a doctor. In contrast, they should go to an emergency room if they have serious symptoms such as chest pain.

There is a link between certain heart sounds and atrial fibrillation. The condition is usually, but not always, associated with an irregular rhythm in the interval between S1 and S2.

Atypical heart sounds do not always indicate atrial fibrillation. They can stem from other causes and may require various diagnostic tests. These may include an EKG, blood tests, and imaging.

In some cases, a heart murmur may cause atrial fibrillation.

Any person with symptoms of atrial fibrillation or any other arrhythmia needs to seek immediate medical attention.