Heart blocks

Medical Presentation

1. HEART BLOCKS Noel Christian Group 6

2. Heart block is an abnormal heart rhythm where the heart beats too slowly ( bradycardia ). In this condition, the electrical signals that tell the heart to contract are partially or totally blocked between the atria and the ventricles. For this reason, it is also called atrioventricular block (AV block).

3. What is Heart Block? A normal heartbeat is initiated by an electrical signal that comes from the heart’s natural pacemaker, the sinoatrial (SA) node, located at the top of the right atrium. The electrical signal travels through the atria and reaches the atrioventricular (AV) node. After crossing the AV node, the electrical signal passes through the bundle of His.

4. This bundle then divides into thin, wire-like structures called bundle branches that extend into the right and left ventricles. The electrical signal travels down the bundle branches and eventually reach the muscle cells of the ventricles, causing them to contract and pump blood to the body. Heart block occurs when this passage of electricity from top to bottom of the heart is delayed or interrupted .

5. Types of Heart Block: First Degree Heart Block The electrical impulses are slowed as they pass through the conduction system, but they all successfully reach the ventricles. First-degree  heart block rarely causes symptoms or problems. Well-trained athletes may have first-degree heart block. Some medications can also cause this condition. No treatment is generally needed for first-degree heart block . PR prolongation , is a disease of the electrical conduction system of the heart in which the PR interval is lengthened beyond 0.20 seconds .

6. Cause AV nodal disease, enhanced vagal tone (for example in athletes), myocarditis , acute myocardial infarction (especially acute inferior MI), electrolyte disturbances and medication. The drugs which can cause first-degree heart block are those that increase the refractory time of the AV node, thereby slowing AV conduction. These include calcium channel blockers, beta-blockers .

7. Diagnosis In normal individuals, the AV node slows the conduction of electrical impulse through the heart. This is manifest on a surface electrocardiogram (ECG) as the PR interval. The normal PR interval is from 120  ms  to 200 ms in length. I n first-degree heart block, the diseased AV node conducts the electrical activity more slowly. This is seen as a PR interval greater than 200 ms in length on the surface ECG. It is usually an incidental finding on a routine ECG not always present.

8. Second-degree heart block The electrical impulses are delayed further and further with each subsequent heartbeat until a beat fails to reach to the ventricles entirely. This type of block most often is physiologic and is seen in a highly relaxed state and during sleep. It rarely causes symptoms. It sometimes causes dizziness and/or other symptoms. There are two non-distinct types of second-degree AV block, called Type 1 and Type 2.

9. Type 1 ( Mobitz I/ Wenckebach ) Type 1 Second-degree AV block, also known as Mobitz I or Wenckebach periodicity, is almost always a disease of the AV node. Mobitz I heart block is characterized by progressive prolongation of the PR interval on consecutive beats followed by a blocked P wave (i.e., a 'dropped' QRS complex). After the dropped QRS complex, the PR interval resets and the cycle repeats . Mobitz I heart block is that the atrial rhythm has to be regular.

10. This is almost always a benign condition for which no specific treatment is needed for the rhythm itself. It can be seen in myocardial ischemia, propranolol use , rheumatic fever, and chronically in ischemic heart disease and other structural diseases (amyloidosis, mitral valve prolapse, aortic valve disease, and atrial septal defect. In symptomatic cases, intravenous atropine or isoproterenol may transiently improve conduction.

11. Sinus rhythm with acute inferior infarction complicated by Type I A-V block

12. Type 2 ( Mobitz II/Hay ) Type 2 Second-degree AV block, also known as " Mobitz II," is almost always a disease of the distal conduction system (His-Purkinje System ). With this condition, some of the electrical impulses are unable to reach the ventricles . This condition is less common than Type I, and is more serious. Usually, your doctor will recommend a pacemaker to treat type II second degree heart block, as it frequently progresses to third degree heart block

13. Mobitz II heart block is characterized on a surface ECG by intermittently nonconducted P waves not preceded by PR prolongation and not followed by PR shortening i.e , fixed P-R interval. The medical significance of this type of AV block is that it may progress rapidly to complete heart block , in which no escape rhythm may emerge. In this case, the person may experience a Stokes-Adams attack, cardiac arrest, or sudden cardiac death. The definitive treatment for this form of AV Block is an implanted pacemaker.

14. Third Degree Heart Block With this condition, also called complete heart block , none of the electrical impulses from the atria reach the ventricles. When the ventricles do not receive electrical impulses from the atria, they may generate some impulses on their own, called junctional or ventricular escape beats. Ventricular escape beats, the heart’s naturally occurring backups, are usually very slow. Patients frequently feel fatigue, lightheadedness, and decreased stamina in complete heart block. Patients are usually treated by implanting a permanent pacemaker.

15. T wo independent rhythms can be noted on the electrocardiogram (ECG ). The P waves with a regular P-to-P interval (in other words, a sinus rhythm) represent the first rhythm. The QRS complexes with a regular R-to-R interval represent the second rhythm. The PR interval will be variable, as the hallmark of complete heart block is lack of any apparent relationship between P waves and QRS complexes.

16. Patients with third-degree AV block typically experience severe bradycardia, hypotension , and at times, hemodynamic instability.

17. Atrial tachycardia with complete A-V block and resulting junctional escape

18. Cause Many conditions can cause third-degree heart block, but the most common cause is coronary ischemia. Progressive degeneration of the electrical conduction system of the heart can lead to third-degree heart block . An inferior wall myocardial infarction may cause damage to the AV node, causing third-degree heart block. An anterior wall myocardial infarction may damage the distal conduction system of the heart, causing third-degree heart block. This is typically extensive, permanent damage to the conduction system, necessitating a permanent pacemaker to be placed.

19. Symptoms of Heart Block Some people with heart block will not experience any symptoms. Others will have symptoms that may include the following: Fainting (syncope ) Dizziness Lightheadedness Shortness of breath Decline in exercise capacity

20. Risk factors for Heart Block Some medical conditions increase the risk for developing heart block. These medical conditions include : Heart failure Prior heart attack Heart valve abnormalities Heart valve surgery Congenital heart diseases Some medications or exposure to toxic substances Lyme disease Aging

21. References   "ECG Conduction Abnormalities" . Retrieved 2009-01-07. Jump up^   "Heart Block" . NHS Choices. National Health Service (UK). Retrieved 25 August 2015. Jump up^   Sclarovsky , S; Strasberg, B; Hirshberg , A; Arditi , A; Lewin, RF; Agmon , J (July 1984). "Advanced early and late atrioventricular block in acute inferior wall myocardial infarction". American Heart Journal.  108  (1): 19–24.  doi : 10.1016/0002-8703(84)90539-8 .  PMID   6731277 . Dretzke , J.; et al.  "Compared to single chamber ventricular pacemakers, dual chamber pacemakers may reduce the incidence of complications in people with sick sinus syndrome and atrioventricular block" . Cochrane reviews. Retrieved 25 August2015. Jump up^   " Peri -arrest arrhythmias" . Resuscitation guidelines. Resuscitation Council UK. Retrieved 25 August 2015 .