First-degree atrioventricular block (AV block) is a disease of the electrical conduction system of the heart in which electrical impulses conduct from the cardiac atria to the ventricles through the atrioventricular node (AV node) more slowly than normal. First degree AV block does not generally cause any symptoms, but may progress to more severe forms of heart block such as second- and third-degree atrioventricular block. It is diagnosed using an electrocardiogram, and is defined as a PR interval greater than 200 milliseconds. First degree AV block affects 0.65-1.1% of the population with 0.13 new cases per 1000 persons each year. Causes
The most common causes of first-degree heart block are AV nodal disease, enhanced vagal tone (for example in athletes), myocarditis, acute myocardial infarction (especially acute inferior MI), electrolyte disturbances and medication. The medications that most commonly 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, cardiac glycosides, and anything that increases cholinergic activity such as cholinesterase inhibitors. Diagnosis
In normal individuals, the AV node slows the conduction of electrical impulses 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. This is measured from the initial deflection of the P wave to the beginning of the QRS complex.In first-degree heart block, the diseased AV node conducts the electrical activity more slowly.
At least 9 IMF cases described in the English literature were diagnosed in fetuses based on the findings of fetal spectrogram and/or magnetic resonance imaging. IMF tumors in the viscera or deep tissues may present with serious or life-threatening signs and symptoms of organ and/or deep tissue damage due to these tumors space-filling and pressuring effects.Some individuals with IMF present with a family history of IMF tumors. To date (2021), 20 families have been reported to carry various germline (i.e. inherited) mutations in one of their two PDGFRB genes. All of these mutations were gain of function mutations (i.e. the mutant genes product is overactive) and inherited in an autosomal dominant manner with incomplete penetrance. Among 36 identified familial carriers of these mutant genes, 4 had no history of IMF, 3 had developed a solitary IMF, 29 had developed multiple tumors (no viscera involvement) or multiple tumors (with viscera involvement) IMF, and 2 had died. Most of these individuals were diagnosed with IMF in their infancy or early childhood. Subsequent studies have found that up to 70% of individuals with IMF and no family history of the disease also carry mutations in one of their two PDGFRB genes in the cells of their tumor tissues. These mutations are somatic mutations (i.e. non-inherited mutations developing only after conception) that are identical or similar to those seen in familial cases. The familial and non-familial mutated PDGFRB genes produce highly overactive platelet-derived growth factor receptor beta (i.e.