Heart Essay, Research Paper

The Normal Cardiac Cycle

During each heartbeat, the two upper chambers (right and left atria) contract, followed by contraction of the two lower pumping chambers (right and left ventricles). This action is coordinated by the heart’s electrical system.

Normal electrical activation of the heart occurs in an orderly fashion. With each beat, the electrical impulse starts in the sinus (or sinoatrial) node (in the right atrium). The impulse spreads through the atria, stimulating the atria to contract. The impulse then reaches the atrioventricular node (AV node), an electrical bridge that allows impulses to go from the atria to the ventricles. There is a short delay in conduction before the impulse goes on to the ventricles. From the AV node, the impulse travels through a pathway of fibers called the His-Purkinje system. This network sends the impulse into the muscular walls of the ventricles and causes them to contract. The contraction pumps blood out of the heart to the lungs and throughout the body.

The rate at which the normal heart beats depends on the body’s need for oxygen-rich blood. When at rest, the body needs less oxygen-rich blood,

so the heart rate may be slower. However, during activity or exercise, the body needs more oxygen-rich blood, and the sinus node causes the heart rate to increase. Taking a pulse tells how fast the heart is beating.

Taking Your Pulse

You can feel your pulse on your wrist. Place your index and middle finger on the inner wrist of your other arm, just below the base of your thumb. Your heart rate, or pulse, is the number of beats felt in one minute. You can count the number of beats in 10 seconds and multiply by 6 to determine your heart rate in beats per minute. By feeling your pulse, you can also tell if your heart rhythm is regular or not.

YOUR HEART RATE = PULSE IN 10 SECONDS x 6 = ____ beats per minute

What is an arrhythmia?

An arrhythmia is an irregular or abnormal heart rhythm. Arrhythmias may have many causes, including coronary artery disease, changes in the heart muscle, valvular disorders, electrolyte imbalances, or injury from a heart attack. Irregular heart rhythms can even occur in a healthy “normal” heart.

Common Types of Arrhythmias

Tachycardia – a fast heart rhythm that has a rate of more than 100 beats per minute.

Bradycardia – a slow heart rhythm that has a rate below 60 beats per minute.

Supraventricular arrhythmias – arrhythmias originating above the ventricles, for example in the upper chambers, or atria. (”Supra” means above; “ventricular” refers to the lower chambers of the heart.)

Premature atrial contractions (PACs) – early, extra beats originating in the upper chambers of the heart.

Paroxysmal supraventricular tachycardia (PSVT) – a rapid, usually regular rhythm originating from above the ventricles that begins and ends

suddenly.

Accessory pathway mediated tachycardias (e.g. Wolff-Parkinson-White syndrome) – tachycardias due to an extra, abnormal electrical pathway or connection between the atria and ventricles.

AV nodal reentrant tachycardia – tachycardia due to more than one pathway through the AV node.

Atrial tachycardia – a rapid rhythm originating in the atria.

Atrial fibrillation – an arrhythmia due to rapid impulses coming from the atria that are disorganized and irregular. Mechanically, this pattern of rapid, disordered atrial activation results in loss of coordinated atrial contraction. Irregular electrical inputs to the atrioventricular (AV) node and His-Purkinje system leads to irregular ventricular contractions.

Atrial flutter – an atrial arrhythmia due to one or more rapid circuits in the atrium. This arrhythmia generally is more ordered than atrial fibrillation.

Ventricular arrhythmias – arrhythmias arising from the lower chambers of the heart.

Premature ventricular contractions (PVCs) – early, extra beats originating in the lower chambers of the heart. PVCs are common. Usually they cause no symptoms and require no treatment. In some people, PVCs can be related to stress, caffeine, nicotine or to exercise. But sometimes, PVCs can be caused by heart disease or electrolyte imbalance. People who have a lot of PVCs and/or symptoms associated with them should be evaluated by a cardiologist.

Ventricular tachycardia – a rapid rhythm originating from the lower chambers. This can be a more serious arrhythmia, particularly in people with heart disease, and may be associated with more symptoms. It should be evaluated by a cardiologist.

Ventricular fibrillation – an erratic, disorganized firing of impulses from the ventricles. The ventricles quiver and cannot generate an effective contraction, causing an inability to deliver blood to the body. It is a medical emergency that must be treated with cardiopulmonary resuscitation (CPR) and defibrillation as soon as possible.

Bradyarrhythmias – slow heart rhythms which may arise from disease in the sinus node and other parts of the heart’s conduction system, including the AV node and His-Purkinje system.

Sinus node dysfunction – slow heart rhythms due to abnormalities in the sinus (sinoatrial) node.

Heart block – a delay or complete blocking of the electrical impulse as it travels from the sinus node to the ventricles. The level of the block or delay may occur in the AV node or His-Purkinje system. The heart may beat irregularly and usually slower.

What are the symptoms of an arrhythmia?

An arrhythmia may be *silent* and may not cause any symptoms. However, a doctor can detect an arrhythmia during an examination by taking the person’s pulse or through a test called an electrocardiogram (ECG). Many people with arrhythmias do have symptoms. These could include any one or more of the following:

Palpitations – sensations of skipped heart beats, fluttering, “flip-flops” or feelings that the heart is “running away”

Pounding in the chest

Dizziness or feeling light-headed

Fainting

Shortness of breath

Chest discomfort

Weakness or fatigue

How are arrhythmias diagnosed and what is the risk assessment?

Diagnosis can be difficult, because arrhythmias may be intermittent and there are many different types. Arrhythmias may need no treatment at all, or they may be a sign that something is wrong and requires further treatment. After evaluating a patient’s symptoms and performing a physical examination, the cardiologist may perform a variety of diagnostic tests to help confirm the presence of an arrhythmia and indicate its causes. This is important to determine the seriousness or potential risk associated with an arrhythmia.

Diagnostic Tests

Some tests that may be done to confirm the presence of an arrhythmia include:

Electrocardiogram (ECG) – a picture, on graph paper, of the electrical impulses traveling through the heart muscle, recorded by electrodes attached to the chest, arms and legs.

Ambulatory monitors – there are several types:

A holter monitor is a small portable recorder that is attached to electrodes on the chest and that can record the heart rhythm continuously for 24 hours at a time.

A transtelephonic monitor records events when the patient is hooked to electrode leads connected to a device that can transmit the rhythm over a telephone.

A transtelephonic monitor with a memory loop can be worn continuously for prolonged periods and records and saves the rhythm around the time that an event button is activated. After recording, the rhythm recorded and saved can be transmitted over the telephone.

Stress test – An exercise test which may be particularly useful in recording arrhythmias that can be brought on with stress or exercise. This test may also be helpful in determining if there is underlying heart disease or coronary artery disease associated with an arrhythmia.

Echocardiogram – An ultrasound of the heart may be useful in determining if there is any associated heart muscle or valve disease that may be causing an arrhythmia.

Cardiac catheterization – During this test, using local anesthetics, a catheter is inserted into a blood vessel and guided to the heart with the aid of an X-ray machine. A contrast dye is injected through the catheter so that X-ray movies of the coronary arteries, heart chambers, and valves may be taken. This test may be ordered by a physician to determine if the cause of an arrhythmia is coronary artery disease and to give information about how well the heart muscle and valves are working.

Electrophysiology study (EPS) – A special heart catheterization that studies the heart’s electrical system. The catheters inserted can record the electrical activity within the heart and are used to help find the cause of the rhythm disturbance and the best treatment. During the test, the arrhythmia may be safely reproduced and terminated.

Head upright tilt test (HUT) – A test used to safely reproduce fainting spells in people that may be prone to vasovagal fainting episodes. During the test, the patient is tilted on a special table to 60 or more degrees upright. Blood pressure and heart rhythm are recorded. In susceptible individuals, a fainting spell may be provoked. A medication that may facilitate the reproduction of these spells may also be used in conjunction with the tilt procedure.

How are arrhythmias treated?

Treatment decisions may be complex. In some cases, no treatment is necessary. For arrhythmias that are associated with significant symptoms or arrhythmias which may potentially be life-threatening, treatment is often necessary. Treatment options depend on the type and significance of the

arrhythmia. Treatment options may include medications, cardioversion, pacemakers, implantable cardioverter-defibrillators, surgery, or radiofrequency catheter ablation of the arrhythmia focus.

Treatment Options

Medication – Antiarrhythmic drugs are medications that treat or control arrhythmias. A variety of antiarrhythmics are available, and because everyone is different, it may take trials of several agents to find a medication and dose that works best.

Electrical cardioversion – In patients with persistent arrhythmias (for example, atrial fibrillation), a normal rhythm may not be achievable with drug therapy alone. After administration of a short-acting general anesthetic, cardioversion is performed by delivering an electrical shock to the chest wall that synchronizes the heart and allows the normal rhythm to restart.

Permanent pacemaker – A device that sends small electrical impulses to the heart muscle to maintain a suitable heart rate. Pacemakers primarily prevent the heart from beating too slowly. Some pacemakers can increase the heart rate with activity. The pacemaker has two parts: the leads and the pulse generator. Newer pacemakers have many sophisticated features that are designed to help with the management of arrhythmias and to optimize heart rate-related function as much as possible.

Implantable cardioverter-defibrillator (ICD) – A sophisticated device that is used primarily to treat ventricular tachycardia and ventricular fibrillation, two life-threatening heart rhythms. In both cases, the heart beats very fast and requires urgent treatment or death can occur. The ICD constantly monitors the heart rhythm. When it detects a very fast, abnormal heart rhythm, it delivers energy to the heart muscle to cause the heart to beat in a normal rhythm again. There are several ways an ICD can restore a normal heart rhythm. When the heart beats too fast, a series of small electrical impulses may be delivered to the heart muscle to restore a normal heart rate and rhythm (Anti-tachycardia pacing, or ATP).

Implantable cardioverter-defibrillator – A low energy shock may be delivered at the same time as the heartbeat to restore a normal heart rhythm (Cardioversion). When the heart is beating dangerously fast or irregularly, a higher energy shock may be delivered to the heart muscle to restore a normal rhythm (Defibrillation). In addition, many ICDs provide back-up pacing to prevent too slow of a heart rhythm (Anti-bradycardia pacing).

Radiofrequency catheter ablation (RFA) – May be used to cure certain types of arrhythmias and is usually performed in conjunction with an electrophysiology study. During RFA, a special machine is used to direct high radio-frequency energy through a special catheter to small areas of tissue that cause abnormal heart rhythms. This energy “disconnects” the pathway of the abnormal rhythm. RFA is very effective in curing most PSVTs, atrial flutter, and some atrial and ventricular tachycardias. It can also be used to disconnect the electrical pathway between the upper chambers (atria) and the lower chambers (ventricles), which may be useful in people with atrial fibrillation and ventricular rates that cannot be well controlled on medication.

Open heart surgery – May be indicated to correct valvular disease or to bypass coronary artery disease that may predispose to arrhythmias. In addition, surgical procedures are available to potentially cure some arrhythmias in appropriately selected people. For example, the Maze procedure is designed to cure atrial fibrillation in some people with very hard to control atrial fibrillation.

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