2.3.3 Arrhythmia
An arrhythmia is an irregular heartbeat due to a disorder of impulse production，impulse conduction，and in some instances，both（Fig.2-5）.Bradycardia is a slowerthan-average heart rate，and tachycardia is a higher-than-average heart rate.
Fig.2-5 Cardiac Arrhythmia
Auscultation can occasionally detect arrhythmia，however，its diagnosis is often dependent on 12 lead electrocardiogram（ECG）.A few cases require an electrophysiology study that is much more invasive and involves sedation and placing a catheter into the heart，usually through the arteries of the groin.A treadmill（or chemical）stress test is required to provoke arrhythmia，which is then recorded on ECG.
In cases of myocardial infarction（MI），there is often fibrillation，an extremely rapid yet ineffective beating of the heart.MI may also result in heart block，an interruption in the electrical conduction system of the heart.Atrial fibrillation，a supraventricular arrhythmia，allows blood to stagnate in the heart and form clots.These clots could result in an embolic stroke.A transesophageal echocardiogram is required for any patient in atrial fibrillation to ensure clots have not formed during the arrhythmia and before returning the patient to conversion to normal sinus rhythm.Ventricular fibrillation requires an immediate response，such as defibrillation，to prevent degeneration into asystole，cardiogenic shock，and death.
Cardioversion is the general term for restoration of a normal heart rhythm.Cardioversion is usually done by sending shocks to your heart through electrodes placed on your chest.It’s possible also to do cardioversion with medications.Several devices are in use for electrical defibrillation.If，for any reason，the sinoatrial node is not generating a normal heartbeat，an artificial pacemaker（Fig.2-6）may be implanted in the chest to regulate the beat.
Fig.2-6 Artificial Pacemaker
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Task 5 Fill in the blanks with proper words.(https://www.daowen.com)
1.Arrhythmia might be attributed to a disorder of impulse production and（or）impulse________.
2.Bradycardia refers to the heartbeat at a slower-than-average rate.________refers to the heartbeat at a higher-than-average rate.
3.The purpose of a（n）________study is to record intracardiac signals and to assess their timing and their relationship to the simultaneously recorded ECG signals.
4.Atrial________is a quivering or irregular heartbeat that can lead to blood clots，stroke，heart failure and other heart-related complications.
5.________occurs when the electrical signals from the top chambers of your heart don’t conduct correctly to the bottom chambers of your heart.
6.A（n）________arrhythmia is an irregular heart rate that begins above the ventricles.
7.A（n）________ECG is a type of test that is done by inserting a long and thin tube with a transducer down the esophagus.
8.Defibrillation should be done immediately for patients with ventricular fibrillation to prevent________shock.
9.________can be achieved either by medication or by application of electric current.
10.An artificial________is an electronic device implanted in the chest to maintain or restore a normal rhythm in people with abnormal heart rhythms.