Various factors can change the cardiac rate and rhythm, resulting in an arrhythmia. Arrhythmias can be caused by changes in rate (tachycardia, which is a faster-than-normal heart rate, or bradycardia, which is a slower-than-normal heart rate); by stimulation from an ectopic focus, such as premature atrial contractions (PACs) or premature ventricular contractions (PVCs), atrial flutter, atrial fibrillation (AF), or ventricular fibrillation; or by alterations in conduction through the muscle, such as heart blocks and bundle branch blocks.
1. Normal sinus rhythm. Rhythm: Regular. Rate: 60 to 100 beats/min. P–R interval: 0.12 to 0.20 seconds. QRS: 0.06 to 0.10 seconds.
正常窦性心律。心律：正常；心率：60-100 beats/min。P-R间期：0.12-0.20 s; QRS：0.06-0.10 s。
2. Atrial arrhythmias: Premature atrial contractions (PACs). Rhythm: Irregular due to the origination of a beat outside the normal conduction system (ectopic). Rate: Normal sinus rate, except for PACs. P–R interval: P wave is abnormal, and interval may be slightly shortened in ectopic beat. QRS: Normal.
房性心律不齐：房性期外收缩（PACs）。心律：不规则，由正常传导系统外（异位）心跳的起始引起。心率：正常窦性心率，PACs除外。P-R间期：P波正常，异位心搏间期略有缩短。QRS：正常。
3. Atrial fibrillation. Rhythm: Irregularly irregular. Rate: Variable; usually rapid on initiation of rhythm; decreases when controlled by medication. P–R interval: No P waves are seen, replaced by an irregular wavy baseline. The atria are fibrillating because impulses are arising at a rate greater than 350 per minute. The ventricles respond when the atrioventricular (AV) node is stimulated to threshold and can receive the impulse. QRS: Normal.
心房纤颤。心律：不规则。心率：多变；心律起始时通常快；药物控制时下降。P-R间期：无P波，被不规则波形基准线取代。心房因冲动以＞350/min速率上升而颤动。AV结刺激达到阈值时心室响应，可以接收冲动。QRS：正常。
4. Premature ventricular contractions (PVCs) or ventricular premature beats (VPBs). Rhythm: Irregular. Rate: Variable; only interrupts the cycle of the ectopic, ventricular contraction. P–R interval: Normal in sinus beats, not measurable in PVCs. QRS: Wide, bizarre, greater than 0.12 seconds.
室性期外收缩（PVCs）或室性期外搏动（VPBs）。心律：不规则。心率：多变；只破坏异位、心室收缩周期。P-R间期：窦性搏动正常，PVCs时测量不到。QRS：宽、不协调，＞0.12 s。
5. Ventricular fibrillation. Rhythm: Irregular. Rate: Not measurable. P–R interval: Not measurable. QRS: Not measurable, replaced by an irregular wavy baseline. No coordinated electrical or mechanical activity in the ventricle, no cardiac output.
心室颤动。心律：不规则。心率：不可测。P-R间期：不可测。QRS：不可测，被不规则波形基准线取代。心室无协调性电或机械活动，无心排血量。
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Atrial Rhythms
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1. Johanna has ventricular ectopy, which of the following drugs is the first line used to treat her condition?
A. Qinidine (Cardioquin).
B. Digoxin (Lanoxin).
C. Procainamide ( Pronestyl).
D. Lidocaine (Xylocaine). 2. Class IA antiarrhythmic agents have little effect on:
A. AV node.
B. SA node.
C. Purkinje fibers.
D. Bundle of His.
奥医教育“在线自测”题库
ISPN/RN复习练习、效果检验一站完成。
答案 Answer
1. D. Lidocaine (Xylocaine). Rationale: Lidocaine is the only choice used to treat ventricular ectopy. A and C are class IA antiarrhythmics. 2. B. SA node. Rationale: Class IA antiarrhythmics have little effect on the SA node. It causes moderate degree blockage of fast sodium channels. Drugs include quinidine, procainamide, and disopyramide. These are the most pro-arrhythmic of the sodium channel blockers due to prolonged QTc interval; use is limited due to proarrhythmic potential.
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