Your Heart and Its Normal Components

To understand how the heart pumps, learn about:

Structure of the Heart

Structure of the heart: four chambers, four valves

The heart has four chambers, two on the right and two on the left:

• Two upper chambers are called atria (one is called an atrium).
• Two lower chambers are called ventricles.

The heart also has four valves that open and close to let blood flow in only one direction when the heart contracts (beats). The four heart valves are:

• Tricuspid valve, located between the right atrium and right ventricle
• Pulmonary or pulmonic valve, between the right ventricle and the pulmonary artery
• Mitral valve, between the left atrium and left ventricle
• Aortic valve, between the left ventricle and the aorta

Each valve has a set of flaps (also called leaflets or cusps). The mitral valve has two flaps; the others have three.

Blood flow occurs only when there's a difference in pressure across the valves, which causes them to open.

Under normal conditions, the valves permit blood to flow in only one direction.

The heart pumps blood to the lungs and to all the body's tissues by a sequence of highly organized contractions of the four chambers. For the heart to function properly, the four chambers must beat in an organized way.

Electrical System of the Heart

Electrical signals control the pump

The heart beat (contraction) begins when an electrical impulse from the sinoatrial node (also called the SA node or sinus node) moves through it. The SA node is sometimes referred to as the heart's "natural pacemaker" because it initiates impulses for the heartbeat.

The normal electrical sequence begins in the right atrium and spreads throughout the atria to the atrioventricular (AV) node. From the AV node, electrical impulses travel down a group of specialized fibers called the His-Purkinje System (the Bundle of His) to all parts of the ventricles.

This exact route must be followed for the heart to pump properly. As long as the electrical impulse is transmitted normally, the heart pumps and beats at a regular pace. In an adult, a normal heart beats 60 to 100 times a minute.

Electrocardiography (ECG or EKG) is a painless, non-invasive procedure that records the heart’s electrical activity and can help diagnose arrhythmias.

Abnormal Heart Rhythms (arrhythmias)

Arrhythmias are abnormal beats. The term "arrhythmia" refers to any change from the normal sequence of electrical impulses, causing abnormal heart rhythms. Arrhythmias may be

• completely harmless or
• they can be life-threatening.

Some Arrhythmias are so brief (for example, a temporary pause or premature beat) that the overall heart rate or rhythm isn't greatly affected.

But if Arrhythmias last longer, they may cause the heart rate to be too slow or too fast or the heart rhythm to be erratic – so the heart pumps less effectively.

• A fast heart rate (in adults, more than 100 beats per minute) is called tachycardia.
• A slow heart rate (less than 60 beats per minute) is referred to as bradycardia.

Causes

• Normally, the heart's most rapidly firing cells are in the sinus (or sinoatrial or SA) node, making that area a natural pacemaker.
• Under some conditions almost all heart tissue can start an impulse of the type that can generate a heartbeat. Cells in the heart's conduction system can fire automatically and start electrical activity. This activity can interrupt the normal order of the heart's pumping activity.
• Secondary pacemakers elsewhere in the heart provide a "back-up" rhythm when the sinus node doesn't work properly or when impulses are blocked somewhere in the conduction system.

An Arrhythmia occurs when:

• The heart's natural pacemaker develops an abnormal rate or rhythm.
• The normal conduction pathway is interrupted.
• Another part of the heart takes over as pacemaker.

Types of Arrhythmia

Types of Arrhythmias

• Atrial Fibrillation = upperheart chambers contract irregularly
• Bradycardia = slowheart rate
• Conduction Disorders= heart does not beat normally
• Premature contraction = early heart beat
• Tachycardia = very fast heart rate
• Ventricular Fibrillation = disorganized contraction of the lower chambers of the heart
• Other Rhythm Disorders
• Types of Arrhythmia in Children

The normal heart is a strong, muscular pump a little larger than a fist. It pumps blood continuously through the circulatory system.

• Each day the average heart beats (expands and contracts) 100,000 times and pumps about 2,000 gallons of blood through the body.
• In a 70-year lifetime, an average human heart beats more than 2.5 billion times.

Diagnosis, Prognosis, Symptoms and Monitoring

Why Arrhythmia Matters 

The Medical Perspective

When the heart's ability to work is greatly reduced for a prolonged time, a life-threatening situation can arise.

This may result from

• ventricular tachycardia and 
• ventricular fibrillation, an extremely fast, chaotic rhythm during which the lower chambers quiver and the heart can't pump any blood, causing cardiac arrest. This is sudden cardiac arrest, which is a medical emergency.

If the heart can continue to pump normally, though, some ventricular tachycardias may be tolerated without fainting (syncope) or cardiac arrest.

Tachycardia may be

• nonsustained (lasting only seconds) or
• sustained (lasting for minutes or hours).

Tachycardias also can cause serious injury to other organs. For example, the brain, kidneys, lungs or liver may be damaged during prolonged cardiac arrest.

Blood clots can form in the heart's upper chambers because of atrial fibrillation, a disorder in which the atria quiver (like a bowl of gelatin) instead of beating effectively. Blood that isn't pumped completely out of the atria when the heart beats may pool and clot. If a piece of a blood clot in the atria breaks free, it can enter into the circulation. Then it can flow within the bloodstream until it lodges in a narrowed artery leading to or within the brain, causing a stroke. Such clots can also damage other organs.

What is Sudden Cardiac Arrest?

Sudden cardiac arrest is the abrupt loss of heart function in a person who may or may not have diagnosed heart disease. The time and mode of death are unexpected. It occurs instantly or shortly after symptoms appear.

The term "massive heart attack" is often mistakenly used to describe sudden cardiac arrest. While a heart attack may cause cardiac arrest and sudden death, the terms don't mean the same thing. The term "heart attack" (or myocardial infarction) refers to death of heart muscle tissue due to the loss of blood supply, not necessarily resulting in the death of the heart attack victim.

Arrhythmias Can Cause Stroke

Stroke is a Cerebrovascular Disease that affects the blood vessels supplying blood to the brain. A stroke occurs when a blood vessel bringing oxygen and nutrients to the brain bursts or is clogged by a blood clot or some other particle. Because of this rupture or blockage, part of the brain doesn't get the blood flow it needs. Deprived of oxygen, brain cells in the affected area can't function and die within minutes. And when brain or nerve cells can't function, the part of the body they control can't function either. The devastating effects of stroke are often permanent because dead brain cells aren't replaced.

There are two types of strokes:

• those caused by a blocked blood vessel to the brain (ischemic stroke)
• those caused by a ruptured blood vessel (hemorrhagic stroke), blood within the brain tissues)

The most common cause of stroke from an Arrhythmia is Atrial Fibrillation. Atrial Fibrillation can cause blood clots to form in the atria (top chamber of the heart) where they can be pumped out of the heart, to the brain, blocking a blood vessel and causing a stroke.

Treatment for Atrial Fibrillation focuses in part on reducing the risk of stroke. It's important to know and manage all your risk factors for stroke, including Atrial Fibrillation.

Understand Your Risk For Arrhythmia

Expected changes in heart rate occur during physical activity, stress or excitement, and sleep.

The prevalence of atrial and ventricular arrhythmias tends to increase with age, even when there's no clear sign of coronary heart disease.

Acquired Heart Disease --- such as damage caused to the heart muscle by a heart attack --- is the most important factor making a person prone to Arrhythmias.

Scarring or abnormal tissue deposits can cause bradycardia by interfering with the work of the Sinus Node or overall AV conduction. Likewise, they can cause tachycardia (originating in either the atria or ventricles) by causing cells to fire abnormally or by creating islands of electrically inert tissue. (Impulses circulate in a reentrant fashion around these areas.)

If you have Heart Disease, your healthcare team is likely monitoring your heart rhythm with regular EKGs (electrocardiograms). But Arrhythmias that occur infrequently may not be detected. Also, not all Arrhythmias cause detectable symptoms, so be sure to tell your healthcare professionals about any unusual symptoms such as fainting (syncope), difficulty breathing, fatigue, or a “flopping,” fluttering or thumping feeling in your chest.

Certain congenital conditions from birth may make a person prone to Arrhythmias. For example, an incompletely developed conduction system can cause chronic heart block and bradycardia. People born with extra conduction pathways, either near the AV node or bridging the atria and ventricles, are prone to reentrant supraventricular tachycardias.

Many chemical agents may cause Arrhythmias, sometimes with serious consequences. Known factors include high or low blood and tissue concentrations ofa variety of minerals, such as potassium, magnesium and calcium. These play a vital role in starting and conducting normal impulses in the heart.

Addictive substances, especially sugar, alcohol, cigarettes and recreational drugs, can provoke Arrhythmias, as can various cardiac medications. Even drugs used to treat an Arrhythmia may cause another Arrhythmia.

Risk Factors for Atrial Fibrillation

Atrial fibrillation (AFib or AF) can develop in people who have heart failure or have had a heart attack. It's also found in people with heart valve disease, an inflamed heart muscle or lining (endocarditis) or recent heart surgery. Atrial fibrillation is common in persons with hypertension (high blood pressure) or diabetes. Sometimes it's related to congenital heart defects. A problem with your lungs can also affect your heart. That's why A-Fib often appears in people with chronic lung disease, pulmonary embolism, emphysema and asthma. Other factors that affect risk of developing atrial fibrillation are: thyroid disorders, excessive alcohol consumption and cigarette or stimulant drug use (including caffeine).

Gender and Age also affect the odds of developing A-Fib and its severity.  Men are slightly more likely than women to develop A-Fib, but women diagnosed with it carry a longer-term risk of pre-mature death.  Older people are somewhat more likely to have A-Fib than younger people.  

Manage Your Risk Factors

Just having an Arrhythmia increases your risk of heart attack, cardiac arrest and stroke.  Work with your healthcare team and follow their instructions to control other risk factors:

• Reduce high blood pressure
• Control cholesterol levels
• Lose excess weight
• Eat a heart-healthy diet
• Stop smoking and/ Avoid tobacco smoke
• Enjoy regular physical activity
• Alcohol - only use in moderation if at all, speak with your doctor about alcohol use. If you drink alcohol, do so in moderation. This means an average of one to two drinks per day for men and one drink per day for women. (A drink is one 12 oz. beer, 4 oz. of wine, 1/5 oz. of 80-proof spirits, or 1 oz. of 100-proof spirits.)

Children and Arrhythmias

If your child has been diagnosed with an abnormal heart rate, you're probably alarmed. That's understandable. But by learning more about your child's condition, you'll be less afraid. You'll also be better able to care for your child.

About Heart Rhythms 

The heart rate is the number of times the heart beats each minute. In an older child or teenager who's resting, the heart beats about 70 times a minute. In a newborn it beats about 140 times a minute. Usually the heart rhythm is regular. This means the heart beats evenly (at regular intervals). The heart rate changes easily. Exercise makes the heart beat faster. During sleep it slows down.

An abnormal or irregular heartbeat is called an Arrhythmia. The most common irregularity occurs during breathing. When a child breathes in, the heart rate normally speeds up for a few beats. When the child breathes out, it slows down again. This variation with breathing is called Sinus Arrhythmia. It's completely normal.

Sometimes a doctor may find other kinds of Arrhythmia. Then he or she may want to perform some tests. The doctor may also recommend that a pediatric cardiologist (a doctor specializing in children's heart problems) examine your child.

Knowing Your Child's History

Arrhythmias (also called dysrhythmias) may occur at any age. Many times they have no symptoms. Often parents and children never suspect an Arrhythmia and are surprised when a doctor finds one during a routine physical exam. Rhythm abnormalities are usually evaluated much like other health problems. Your child's history — or what you and your child report about the problem — is very important. You may be asked questions like:

• Is your child aware of unusual heartbeats?
• Does anything bring on the arrhythmia? Is there anything your child or the family can do to make it stop?
• If it's a fast rate, how fast?
• Does your child feel weak, lightheaded or dizzy?
• Has your child ever fainted?

Some medicines may make Arrhythmias worse. 

Be sure to tell your doctor about all the prescribed and over-the-counter medications that your child takes. If your child has an Arrhythmia, discuss this with the doctor and ask what to look for.

Symptoms, Diagnosis and Monitoring

Almost everyone has felt their heart beat very fast, felt a "fluttering" in their chest or thought that their heart was "skipping a beat." These can be signs of arrhythmia, or abnormal or irregular heartbeat.

Don't panic if you've occasionally had these symptoms. Arrhythmias are extremely common, especially as you get older. Each year millions of people have them.

Most cases are harmless, but some Arrhythmias are extremely dangerous and require treatment and management. See your doctor if you have felt any of these symptoms to rule out other problems, such as heart disease, and to give you peace of mind.

Medicines Two Choices for You

Symptoms and Tests for Arrhythmia

Symptoms

Arrhythmias can produce a broad range of symptoms, from barely perceptible to cardiovascular collapse and death.

• A single premature beat may be felt as a "palpitation" or "skipped beat."
• Premature beats that occur often or in rapid succession may cause a greater awareness of heart palpitations or a "fluttering" sensation in the chest or neck.

When arrhythmias last long enough to affect how well the heart works, more serious symptoms may develop:

• Fatigue
• Dizziness
• Lightheadedness
• Fainting (syncope) or near-fainting spells
• Rapid heartbeat or pounding
• Shortness of breath
• Chest pain
• In extreme cases, collapse and sudden cardiac arrest

Several tests can help your doctor diagnose an arrhythmia.

Monitor Your Pulse

You should know how to take your pulse in order to monitor your heart rate – especially if you have an artificial pacemaker.

• Put the second and third fingers of one hand on the inside of the wrist of the other hand, just below the thumb OR on the side of your neck, just below the corner of your jaw.
• Feel for the pulse.
• Count the number of beats in one full minute.
• Keep a record of your pulse along with the day and time taken and notes about how you felt at the time. 

Common Tests For Arrhythmia

Holter monitor (continuous ambulatory electrocardiographic monitor)

Suspected Arrhythmias sometimes may be documented by using a small, portable ECG recorder, called a Holter monitor (or continuous ambulatory electrocardiographic monitor). This can record 24 hours (and sometimes more) of continuous electrocardiographic signals. While an ECG is sort of a 12-second "snapshot" of the heart's electrical activity, the Holter monitor is more like a "movie."

As with an ECG, electrodes are taped to the chest. The wires are connected to a portable, battery-operated recorder that can run for 24 to 48 hours. You can do most normal activities while being tested. You may need to keep a diary or log of your activities and symptoms.

At the end of the measurement period, the recorder’s tape or memory is analyzed on a computer that rapidly identifies rhythm disturbances that occurred while you were wearing the monitor. The diary helps your healthcare professional see how your activities or symptoms correspond to recorded events in your heart.

For suspected Arrhythmias that occur less frequently than every day, your doctor might have you wear an event monitor.

Medicines Two Choices for You

What to Discuss with Your Doctor

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Dr. Huntoon's Alternative Perspective and Your Solution