4. Diagnostic electrocardiographic signs of cardiac arrhythmias

 

Cardiac arrhythmia is a term for any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart. The heart beat may be too fast or too slow, and may be regular or irregular.

Some arrhythmias are life-threatening medical emergencies that can result in cardiac arrest and sudden death. Others cause aggravating symptoms such as an abnormal awareness of heart beat (palpitations), and may be merely annoying. Others may not be associated with any symptoms at all, but pre-dispose toward potentially life threatening stroke or embolism.

Some arrhythmias are very minor and can be regarded as normal variants. In fact, most people will sometimes feel their heart skip a beat, or give an occasional extra strong beat - neither of which is usually a cause for alarm.

However, some asymptomatic arrhythmias are associated with adverse events. Examples include increase in risk of blood clotting within the heart, and also an insufficient amount of blood is transported to the heart because of weak heart beat, and thus increases the risk of pulmonary embolism and stroke, or increase in the risk of heart failure, or increase in the risk of sudden cardiac death.

Some, but not all, cardiac arrhythmias are related to pathologic lesions of the cardiac conduction system. Common atrial arrhythmias and first-degree atrioventricular block rarely are explained on the basis of anatomic lesions in specific sites of the conduction system or its blood supply. Second-degree AV block of Mobitz type II, which may be a precursor of complete (third-degree) heart block, commonly, is associated with pathological lesions of uncertain etiology in the branching part of the bundle of His or the bundle branches. Ischemic lesions are found less often, and other pathologic processes rarely are present. Chronic complete heart block most often results from nonspecific, fibrotic interruption of the distal bundle of His, or of the first parts of the bundle branches after their origins. Ischemic lesions are uncommonly the cause of chronic block. High-grade AV block complicating acute myocardial infarction may be associated with infarction of the AV conduction, but often morphologic evidence of ischemia cannot be identified. Congenital variants in anatomy of the conduction system are responsible for some relatively uncommon arrhythmias.

 

Classification of cardiac arrythmias (dysrhythmias)

 

1. Abnormalities of the impulse formation

A. Altered automaticity of the sinoatrial node

Sinus tachycardia

Sinus bradycardia

Sinus arrhythmia

Sick sinus syndrome

B. Increased automaticity of an ectopic pacemaker

Atrial, junctional, idioventricular rhythms

Wandering pacemaker

Parasystole

C. Ectopic arrythmias caused by increased excitability of the myocardium

Premature heart beat

Paroxysmal tachycardias

Atrial and ventricular flutter and fibrillation

2. Abnormalities of conduction function of heart

Sinoatrial block

Atrioventricular block

Intraventricular block

Preexcitation syndromes ( Wolf-Parkinson-White syndrome, Clerk-Levy-Critesco syndrome)