Clinical Management Of Heart Block
Heart Block Treatment
Long Term Prognosis Is Poor
First and second degree heart blocks: Apart from close ECG monitoring and observation of the clinical state, no specific treatment may be indicated. Treatment of the primary condition clears the conduction defect as well. Atropine 0.5mg given intravenously abolishes vagal tone and improves the heart rate in A-V blocks. Isoprenaline or adrenaline given intravenously increases the heart rate and this is lifesaving in an emergency. The heart rate can be maintained at a higher level by giving ephedrine 30mg orally thrice daily. These sympathomimetic drugs have the risk of triggering off serious tacharrhythmias and hence in acute myocardial infarction there are not recommended. In acute myocardial infarction developing heart block, large intravenous doses of dexamethasone (4-8 mg/6h) have been used successfully.
When a patient with myocardial infarction develops progressive heart block leading to complete heart block, it is an indication for transvenous pacing using an external pacemaker and electrode catheter introduced into the right ventricle.
In established complete heart block, long term prognosis is poor and therefore permanent pacemakers are implanted. Pacemaker consists of two components.
- Pause generator which is made of various type of batteries, and
- The lead which can be connected to the heart.
The pulse generator is implanted into the body by making a pocket in the subcutanoue tissue in the infraclavicular area or on the abdominal wall. The generator is connected to one end of the lead and the other end may be placed in the right ventricle transvenously (endocardial pacemaker) or over the left ventricular apex (epicardial pacemaker). Pacemaker technology has advanced considerably so as to reduce the size of the pulse generator and increase its longevity and improve the stability and position of the leads. The interference by other electric and magnetic fields in the environment is also minimized. It is ideal to implant pacemakers early to avoid the development of Stokes-Adams attacks and sudden death.
Electrical System Of The Heart
Other Forms Of Heart Block
Bundle Branch Block (BBB)
His bundle divides into right and left branches, the left further divides into anterosuperior and posteroinferior fascicles. Conduction of impulse below His bundle occurs through the three fascicles (trifascicular conduction). Conduction disturbance occurring in the right bundle disturbance occurring in the right bundle branche (RBB) is known as right bundle branch block (RBBB) and left main bundle as left bundle branch block (LBBB).
Complete left bundle branch block (LBBB)
This involves the main stem of the left bundle. The anterosuperior or posteroinferior fascicle may be selectively affected at times. These are called left anterior hemiblock (LAH) and left posterior hemiblock (LPH) respectively. Sometimes the main left bundle may be affected, along with one or both of its branches.
Right bundle branch block (RBBB)
Interruption of the right bundle may occur as the lone abnormality or along with block of one or both of the branches of the left bundle. The combination of RBBB with LAH or LPH is called bifascicular block. In trifascicular block RBBB exists with LAH and LPH.
Complete interruption of conduction through the bundle branches leads to delay in conduction of impulses in the ventricular muscle and the QRS complex is prolonged beyond 0.12 sec. When there is only delay without complete block of the impulse (partial bundle branch block) the duration of the QRS is between 0.10 and 0.12 sec (normal 0.08sec).
Bifascicular and trifascicular blocks give rise to characteristic ECG patterns. When the bundle branches are blocked, ventricular activation takes place through the remaining bundle or its fascicles. Bundle branch block may result from ischemic heart diseases, sclerodegenerative disorder of the conduction system of the heart, myocarditis, cardiomyopathy, drugs like quinidine and surgical trauma. In addition, RBBB may be seen in atrial septal defect, acute pulmonary embolism, right ventricular dilatation and right ventricular failure. Congenital RBBB may occur rarely.
In myocardial infarction, presence of bifascicular or trifascicular block is considered an indication for temporary transvenous pacing of the heart, since complete heart block of the fatal asshythmias are likely to develop in such patients.
Ventricular Standstill (Ventricular Asystole)
When there is total cessation of stimuli reaching the ventricles, ventricular standstill develops. The ECG shows absence of QRS. Often the P-wave may also be absent. Cardiac asystole may occur in myocardial infarction and other forms of ischemic heart disease or in complete heart block. Treatment involved external cardiac massage and instituting the procedure for cardiac resuscitation.
© 2014 Funom Theophilus Makama