Overall, every 10 ms increase in the corrected QT interval is associated with a 15% increase in arrhythmic risk.As the QT prolonging effects of both genetic variants and acquired causes of LQTS are additive, those with inherited LQTS are more likely to experience TdP if given QT prolonging drugs or if they experience electrolyte problems such as low blood levels of low potassium (hypokalaemia). Similarly, those taking QT prolonging medications are more likely to experience TdP if they have a genetic tendency to a prolonged QT interval, even it this tendency is concealed. Arrhythmias occur more commonly in drug-induced LQTS if the medication in question has been rapidly given intravenously, or if high concentrations of the drug are present in the persons blood. The risk of arrhythmias is also higher if the person receiving the drug has heart failure, is taking digitalis, or has recently been cardioverted from atrial fibrillation. Other risk factors for developing torsades de pointes among those with LQTS include female sex, increasing age, pre-existing cardiovascular disease, and abnormal liver or kidney function. Causes
There are several subtypes of long QT syndrome. These can be broadly split into those caused by genetic mutations which those affected are born with, carry throughout their lives, and can pass on to their children (inherited or congenital long QT syndrome), and those caused by other factors which cannot be passed on and are often reversible (acquired long QT syndrome). Inherited
Inherited, or congenital long QT syndrome, is caused by genetic abnormalities.
The "first hit" in the hypothesis is proposed to be genetic susceptibility and surrounding environmental factors and the "second hit" would be the introduction of the antigen into the respiratory system which causes the exaggerated immune response. Diagnosis
The diagnosis is made through clinical judgement using a combination of findings because there does not exist a single, universal diagnostic criteria for the disease. The diagnosis is most commonly ascertained first with a detailed exposure history followed by a battery of clinical tests including: imaging, histopathology, pulmonary function testing, serology, bronchoscopy, and more. In 2020, official guidelines were published by American Thoracic Society, Japanese Respiratory Society, and Asociación Latinoamericana del Tórax which provides a systematic approach to the diagnosis of HP that relies on high-resolution computed tomography. Exposure History
A detailed occupational, home and environmental exposure history is the first step in diagnosis. Unfortunately, only 60% of inciting antigens are identified in exposure assessment. Re-exposure to the antigen can help aid in diagnosis. Standardized questionnaires have been created to help in obtaining an exposure history although no official questionnaire has been purported. It has been recommended that the questionnaire administered should be relevant to the region in which the exposure has potentially occurred.Detailed exposure assessments are warranted in the cause of damp indoor environments which have the potential to propagate mold throughout the dwelling. The decision to enlist an industrial hygienist should be made based on the answers to evidence based questions during the environmental assessment.