Clinical Manifestations, Diagnosis And Prognosis Of Heart Block
First Degree Block
First degree heart block is an abnormality usually detected by ECG. Second degree heart block causes regular missing of heart beats and the pulse. Unlike benign extrasystoles in which the irregularity disappears with exertion, the irregularity in heart block tends to persist.
Mobitz type II is associated with more serious disorders such as cute myocardial infarction or degenerative disorders of the conduction system. It may also be seen in digitalis toxicity, rheumatic carditis or cor pulmonale. It is considered a more serious block because more often it progresses to complete A-V block.
Complete heart block should be suspected when the heart rate is 30-40/min or less, not increasing with exercise. The patients may complain of palpitation or syncopal attacks on exertion or even at rest. Syncope is transient loss of consciousness as a result of diminution of arterial blood supple to the brain. The patient complains of dimness of vision, a sinking feeling and may become unconscious. In majority of cases, consciousness is regained on falling down due to resumption of cerebral circulation. If the heart beats are not resumed, the patient develops convulsions-Adams-Stokes attacks. These attacks are seen when periods of asystole or transient ventricular tachycardia or ventricular fibrillation occur in complete heart block. This may also be seen where one idioventricular focus changes over to another one. If the heart beat is not resumed within minutes, the condition ends up fatally. When the lesion is fully established and the rhythm is regular even at a slow rate, compensatory mechanisms develop and the frequency of syncopal attacks diminish.
Conducting System Of The Heart
Physical examination reveals slow, high volume pulse, forcible apex beat (due to diastolic overdistension), presence of cannon waves in the jugular veins, widened pulse pressure (high systolic and normal or low diastolic) and varying intensity of the first heart sound. Independent atrial sounds may be heard.
The ECG shows the slow ventricular rate and complete dissociation of the P and QRS complexes.
Diagnosis: Complete heart block should be suspected when the heart rate is slow, with regular rhythm, not responding to mild exertion. The ECG is absolutely necessary to confirm the diagnosis. His bundle electrography gives further information about the site of lesion.
Prognosis: First and second degree heart blocks may resolve completely with treatment or proceed to complete heart block when the lesion is progressive. During the stage of evolution, the prognosis should be guarded. In the stage of evolution and when the lesion is unstable, complete heart block can be fatal due to cardiac arrest or ventricular fibrillation.
© 2014 Funom Theophilus Makama