An implantable cardioverter defibrillator (ICD) is a small device that's placed in your chest or abdomen. This device uses electrical pulses or shocks to help control life-threatening, irregular heartbeats, especially those that could lead the heart to suddenly stop beating (sudden cardiac arrest). If the heart stops beating, blood stops flowing to the brain and other vital organs. This usually causes death if it's not treated in minutes.

The Heart's Electrical System

Your heart has its own internal electrical system that controls the speed and rhythm of your heartbeat. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the electrical signal causes the heart to contract and pump blood.

Electrical signals normally begin in a group of cells called the sinus node. As these signals spread from the top to the bottom of the heart, they coordinate the timing of heart cell activity. First, the two upper chambers of the heart, called atria (AY-tree-uh), contract. This contraction squeezes blood into the lower chambers of the heart, which are called ventricles (VEN-trih-kuls). The ventricles then contract and send blood to the rest of the body. The combined contraction of the atria and ventricles is a heartbeat.

For more information about the heart's electrical system and how a healthy heart works, see the Diseases and Conditions Index article on How the Heart Works.

Overview

A problem with any part of the electrical system process can cause irregular heartbeats called arrhythmias (ah-RITH-me-ahs). During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. Faulty electrical signaling in the heart causes arrhythmias.

ICDs use electrical pulses or shocks to treat life-threatening arrhythmias that occur in the ventricles (lower chambers of the heart).

When these ventricular arrhythmias occur, the heart can't effectively pump blood, and a person will pass out within seconds and die within minutes if not treated. To prevent death, the condition must be treated right away with an electric shock to the heart. This treatment is called defibrillation.

An ICD has wires with electrodes on the ends that connect to the chambers of your heart. The ICD will continually monitor your heart rhythm. When the device detects that you're having an irregular rhythm in your ventricles, the ICD will use low-energy electrical pulses to restore a normal rhythm. If this doesn't restore your normal heart rhythm, or if your ventricles start to quiver rather than contract strongly, the ICD will switch to high-energy electrical pulses for defibrillation.

Doctors also treat irregular heartbeats with another device called a pacemaker. An ICD is similar to a pacemaker, but there are some differences. Pacemakers can only give off low-energy electrical pulses. They are often used to treat less dangerous heart rhythms, such as those that occur in the upper chambers of your heart. Most new ICDs can act as both pacemakers and ICDs.

Comparison of an Implantable Cardioverter Defibrillator and a Pacemaker

The illustration compares an implantable cardioverter defibrillator and a pacemaker. Figure A shows the location and general size of an implantable cardiac defibrillator in the upper chest. The wires with electrodes on the ends are inserted into the heart through a vein in the upper chest. Figure B shows the location and general size of a double-electrode pacemaker in the upper chest. The wires with electrodes on the ends are inserted into the heart through a vein in the upper chest.

For more information, see the Diseases and Conditions Index article on Pacemaker.

参考翻译(suggested translation)

植入性心律转复除颤器（ICD）是一种体积很小而且能够植入患者胸腔或者腹腔的医疗设备。这种设备会通过电脉冲或者电击来协助控制一些可能致命的心律不齐，有些心律不齐甚至会导致心脏骤停。如果心脏停止跳动，心脏就不会再流向脑部和其他重要器官了。如果在数分钟内不进行抢救，经常会导致患者死亡。

心脏电系统

心脏有着自己的电系统来控制心跳的节奏和速度。随着每一次心跳，电信号都会从心脏顶部传导至底部。而且这些电信号的传输也会引起心脏的收缩，从而达到心脏输送血液的目的。

电信号通常都由一个称为细胞群的窦房结产生。这些信号在传输的过程中（从心脏顶部传送到心脏底部）控制着心脏各部分细胞活动的时序。首先，这些电信号会导致心脏上部两个腔室（心房）收缩，从而将血液压入心脏下部的两个腔室（心室）。这两个心室然后在收缩并将血液输送到身体的其它部分。这种心房和心室收缩的结合称为一次心跳。

关于心脏电系统以及健康心脏如何工作的更多信息，可以参看疾病与症状索引部分的心脏怎样工作部分。

概览

心脏电系统任何部分的问题都会导致心律不齐。心律不齐表现为心跳过快、过慢或心跳节律不规则。心脏内电信号的故障会引起心律不齐。

植入性心律转复除颤器（ICDs）通常利用电脉冲或电击来治疗发生于心室的致命性的心律不齐。

当发生室性心律不齐时，心脏就会失去高效泵血的能力，患者在数秒之内就会昏倒。如果数分钟内不加以治疗，患者可能就会死亡。为了避免死亡，这种症状必须马上通过对心脏电击进行治疗。这种治疗又称为“除颤”。

植入性心律转复除颤器（ICD）上都会伸出几根导线，而这些导线另一端是可以连接到心脏腔室的电极。这样ICD就可以持续地监控患者的心律。当ICD检测到患者的心室内出现心律不整时，就会对心脏释放出电流脉冲来恢复其正常的心跳。如果这样不能使患者恢复正常的心律，或者患者的心室开始出现颤动（而不是有力正常的收缩），ICD就会对心脏释放出高能量的电脉冲（电击）来达到除颤的目的。

医生还会使用另外一种称为“心脏起搏器”的设备来治疗心律不齐。ICD（植入性心律转复除颤器）不但体积比心脏起搏器要小，其他方面也有不同的地方。比如，心脏起搏器只能释放出低能量的电脉冲，所以一般用于症状较轻的心律不齐（比如仅发生于心房内的心律不齐）。目前大多数新型的ICD既具有心脏起搏器的功能，也拥有普通ICD的功能。

植入性心律转复除颤器与心脏起搏器的比较

图A：

Electrodes in heart：心脏内的电极

Right atrium and ventricle：右心房和右心室

Electrodes inserted into vein leading to heart：可抵达心脏的静脉内插入的电极

Implantable defibrillator inserted under skin：位于皮下的植入性除颤器

图B：

Electrodes in heart：心脏内的电极

Pacemaker：心脏起搏器

上面插图对ICD（植入性心律转复除颤器）和心脏起搏器做了比较。图A显示了胸腔上部植入性心律转复除颤器通常的大小和植入位置。而其一端有电极的连线通过胸腔上部的静脉插入心脏。图B显示了胸腔上部双极心脏起搏器通常的大小和植入位置，而一端有电极的连线也是通过胸腔上部的静脉插入心脏

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