Section Two: Internal Disease　第二部分　内科疾病

The primary function of the heart is to supply blood and nutrients to the body. The regular beating, or contraction, of the heart moves the blood throughout the body. Each heartbeat is controlled by electrical impulses traveling through the heart. In the normal heart these electrical impulses occur in regular intervals. When something goes wrong with the heart's electrical system, the heart does not beat regularly. The irregular beating results in a rhythm disorder, or arrhythmia.

The electrical system regulating heartbeat consists of two main areas of control and a series of conducting pathways, similar to the electrical wiring in a house.

●The sinoatrial, or SA, node is located in the right atrium. It is the source and main control and is the source of each heartbeat. The SA node responds to the body's overall need for blood and increases the heart rate when necessary, such as during exercise, emotional excitement, or illness such as fever. The SA node is sometimes called the “natural pacemaker” of the heart.

●Electrical impulses leave the SA node and travel through special conducting pathways in the heart to the other area of control, the atrioventricular (AV) node. The AV node provides a pathway for impulses from the atria to the ventricles. It also creates a delay in conduction from the atria to the ventricle. This causes the atria to contract first and allow the ventricles to fill with blood before they contract themselves.

●The delay ensures proper timing so that the lower chambers have time to fill completely before they contract.

●Normally, the heart beats 60-100 times a minute. This state is called “normal sinus rhythm” or “normal rhythm.” Depending upon the needs of the body, it may beat faster (sinus tachycardia) due to stress or slower (sinus bradycardia) such as during sleep.

Arrhythmias are abnormalities of the heartbeat. There are many types of arrhythmias, and they are classified by where they begin, (the atria, AV node, or the ventricles). Generally speaking, those that do not originate from the ventricles are called supraventricular arrhythmias while those that come from the ventricles are called ventricular arrhythmias.

The following are some of the more commonly encountered arrhythmias, starting with the supraventricular arrhythmias.

●Premature atrial contractions (sometimes called PACs, APCs, or premature supraventricular contractions): PACs are an extra heart beat arising from the atria, outside of the SA node, that causes the heart to contract earlier than expected. This is a very common occurrence in all ages and usually is not serious.

●Supraventricular tachycardia, or paroxysmal SVT: SVTs are regular, rapid heartbeats resulting from abnormal electrical impulses above the ventricle (usually the atria or the AV node).

●Sick sinus syndrome: This syndrome is characterized by irregular firing of the SA node resulting in both slower and faster-than-normal heart rates.

●Atrial fibrillation: A common condition caused by electrical impulses discharged at a rapid rate from many different areas of the atria. It usually causes a fast and irregular heartbeat.

●Atrial flutter: A condition caused by a rapid discharge of abnormal electrical impulses from the right atrium. Typically, the right atrium fires at a rate of 300 beats per minute, but only every other beat is conducted through the AV node, meaning that the ventricular rate is classically 150 beats per minute.

Arrhythmias arising in the ventricle are more likely to be found in people with more serious heart disease but may also be found in healthy individuals.

Premature ventricular complex, or PVCs: This abnormal electrical impulse arises from the ventricle, causing the heart to beat earlier than expected. Usually, the heart returns to its normal rhythm right away.

Ventricular tachycardia: Fast and usually regular impulses come from the ventricles and cause a very rapid heart rate. This is usually a life-threatening tachycardia and needs immediate medical attention and potentially treatment with an electrical shock or defibrillation.

Ventricular fibrillation: Electrical impulses arise from the ventricles in a fast and disordered sequence. The resulting uncoordinated contractions cause the heart to lose its ability to beat and pump blood. The condition usually causes fainting and collapse, and is fatal if not treated immediately.

Arrhythmias can be frightening, but in many cases, especially in younger patients with normal underlying hearts, they are not life threatening and can be effectively treated with medications.

Supraventricular arrhythmias are very common in middle-aged and elderly adults. The older you get, the more likely you are to experience an arrhythmia, especially atrial fibrillation.

Many supraventricular arrhythmias are temporary and not serious, especially if no underlying heart disease is present. These arrhythmias are a response to normal activities or emotions.

Even if an arrhythmia has a serious underlying cause, the arrhythmia itself may not be dangerous. The underlying problem can often be treated effectively.

Among individuals without known heart disease, arrhythmias are generally random, isolated occurrences that do not carry any significance. However, a discussion with a doctor is advised.

A variety of heart diseases cause arrhythmias. Heart disease can refer to patients with coronary artery disease, heart valve problems, heart failure, or disorders with heart conduction or high blood pressure. Remember, however, that having an arrhythmia does not necessarily mean that you have heart disease. Arrhythmias have many causes; sometimes the cause of an arrhythmia is never determined.

Sometimes, conditions other than heart disease may cause or aggravate arrhythmias. These conditions include the following:

●Infection or fever

●Physical or emotional stress

●Diseases such as anemia or thyroid disease

●Drugs and other stimulants, such as caffeine, tobacco, alcohol, cocaine, amphetamines, and certain over-the-counter and prescription medications

●Certain arrhythmias can be inherited as well

Many arrhythmias cause no or minimal symptoms. Other people, however, can actually feel the arrhythmia when it happens.

Common symptoms include the following:

●Palpitations, feeling “skipped beats”

●Thumping or fluttering in the chest

●Sensation of the heart racing

In addition, some can experience the following:

●Feeling faint or tired

●Light-headedness or passing out (syncope)

●Shortness of breath

●Chest pain or discomfort

On the other hand, people may feel many of the sensations described above and have no arrhythmias whatsoever. These may be due to anxiety, stress, or other causes besides an abnormal heartbeat.

Most people have noticed their heart racing, a fluttering in the chest, or a sensation that the heart skipped a beat. If this happens once, or infrequently, with no other symptoms, it is usually not serious. However, any questions or concerns should be discussed with a health care provider. The health care provider should also be notified if a recommended treatment does not alleviate the symptoms.

More serious symptoms should be evaluated immediately at the nearest hospital emergency department. These symptoms include:

●Any unexplained shortness of breath

●Light-headedness or feeling faint

●Feeling that the heart is beating too slowly or too quickly

●Chest pain with any of these symptoms

Evaluation of heart rhythm disorders requires a discussion of symptoms and a physical exam with a health care provider.

In addition, an electrocardiogram (ECG) is mandatory to establish the exact type of arrhythmia. If the rhythm disturbance is present while the ECG is being recorded, the problem can be identified immediately. Otherwise, more specialized testing may be required. A 24-hour (or longer) recording of the heartbeat is often necessary to detect any rhythm problem that occurs daily but not constantly.

However, if the arrhythmia is even more infrequent, an event recorder may be used. These vary from hand-held machines that are activated by the patient whenever he or she feels symptoms, to some that are placed surgically under the skin and left there for up to one year.

An ultrasound of the heart, called an echocardiogram, is often used for an evaluation of the structure and function of the heart. In more serious cases, a test using electrodes placed inside the heart, called an electrophysiologic study (EPS), may be recommended to determine further management.

The treatment of heart rhythm disorders varies depending on the presence or absence of symptoms, how frequent the arrhythmia occurs, and the seriousness of any underlying heart condition. The treatment may range from medication to more advanced surgical procedures, such as an internal implanted cardiac defibrillator (ICD). Sometimes no treatment is necessary. At times, simple or specialized pacemakers may be required to control arrhythmias.

A detailed discussion of the tests and treatment options should be done with the health care provider.

The choice and use of medications depends on the specific type of heart rhythm disorder you have.

Follow-up for a heart rhythm disorder is usually done with the primary care provider and often with a heart specialist. The patient is monitored for effectiveness of treatment, recurrence of symptoms or arrhythmia, side effects of medication, additional routine testing, and overall condition. For those requiring pacemakers, follow-up on a regular basis is mandatory.

aggravate ['ægrəveit] vt.加重,恶化

alleviate [ə'liːvieit] vt.减轻,缓和

arrhythmia [ə'riθmiə] n.心律不齐，心律失常

fainting ['fentiŋ] n.晕厥

mandatory ['mændətɔri] adj.强制的，命令的

palpitation [,pælpi'teʃnz] n.心悸，颤动

sinoatrial [,sainəu'etriəl] n.窦房的

syncope ['siŋkəpi] n.晕厥

atrial fibrillation 心房纤颤

atrial flutter 心房扑动

atrioventricular node 房室结

conducting pathways 传导通路

electrical defibrillation 电除颤

electro physiologic study (EPS) 电生理学研究

emergency department 急诊科

implanted cardiac defibrillator (ICD) 植入心脏除颤器

normal sinus rhythm 正常窦性心律

premature atrial contractions 房性期前收缩

premature ventricular complex 室性期前收缩

sick sinus syndrome 病态窦房结综合征

sinus bradycardia 窦性心动过缓

sinus tachycardia 窦性心动过速

supraventricular tachycardia 室上性心动过速

ventricular fibrillation 室颤

ventricular tachycardia 室性心动过速