Third-degree atrioventricular block
Third-degree AV block occurs when the signal between the atria and ventricles is completely blocked, and there is no communication between the two. None of the signals from the upper chambers makes it to the lower chambers. On ECG, there is no relationship between P waves and QRS complexes, meaning the P waves and QRS complexes are not in a 1:1 ratio.Third-degree AV block is the most severe of the AV blocks. Persons with third-degree AV block need emergency treatment including but not limited to a pacemaker. Etiology
There are many causes of AV block, ranging from a normal variant among people to the result of a heart attack.First-degree AV block and Mobitz I second-degree block are often thought to be just normal, benign, conditions in people, and do not often result from a severe underlying condition.Mobitz II second-degree block and third-degree AV block are not normal variants and are associated with an underlying condition. Common causes include ischemia (lack of blood flow and oxygen to the heart muscle) or progressive fibrosis (excessive scaring) of the heart. It is also possible that a high degree block can result after cardiac surgery during which the surgeon was in close proximity to the electrical conduction system and accidentally injured it. Reversible causes of Mobitz II and third-degree heart block include untreated Lyme disease, hypothyroidism, hyperkalemia (high levels of potassium), and drug toxicity.
Bronchiolitis may be differentiated from some of these by the characteristic pattern of preceding febrile upper respiratory tract symptoms lasting for 1 to 3 days followed by the persistent cough, tachypnea, and wheezing. However, some infants may present without fever (30% of cases) or may present with apnea without other signs or with poor weight gain prior to onset of symptoms. In such cases, additional laboratory testing and radiographic imaging may be useful. The following are some other diagnoses to consider in an infant presenting with signs of bronchiolitis:
Asthma and reactive airway disease
Bacterial pneumonia
Congenital heart disease
Heart failure
Whooping cough
Allergic reaction
Cystic fibrosis
Chronic pulmonary disease
Foreign body aspiration
Vascular ring

Prevention
Prevention of bronchiolitis relies strongly on measures to reduce the spread of the viruses that cause respiratory infections (that is, handwashing, and avoiding exposure to those symptomatic with respiratory infections). Guidelines are mixed on the use of gloves, aprons, or personal protective equipment. In addition to good hygiene, an improved immune system is a great tool for prevention.One way to improve the immune system is to feed the infant with breast milk, especially during the first month of life. Respiratory infections were shown to be significantly less common among breastfed infants and fully breastfed RSV-positive hospitalized infants had shorter hospital stays than non or partially breastfed infants.