In response to a triggering impulse, the waves of depolarisation will spread through regions with shorter action potentials but block in regions with longer action potentials. This allows the depolarising wavefront to bend around areas of block, potentially forming a complete loop and self-perpetuating. The twisting pattern on the ECG can be explained by movement of the core of the re-entrant circuit in the form of a meandering spiral wave. Diagnosis
Diagnosing long QT syndrome is challenging. Whilst the hallmark of LQTS is prolongation of the QT interval, the QT interval is highly variable among both those who are healthy and those who have LQTS. This leads to overlap between the QT intervals of those with and without LQTS. 2.5% of those with genetically proven LQTS have a QT interval within the normal range. Conversely, given the normal distribution of QT intervals, a proportion of healthy people will have a longer QT interval than any arbitrary cutoff. Other factors beyond the QT interval should therefore be taken into account when making a diagnosis, some of which have been incorporated into scoring systems. Electrocardiogram
Long QT syndrome is principally diagnosed by measuring the QT interval corrected for heart rate (QTc) on a 12-lead electrocardiogram (ECG). Long QT syndrome is associated with a prolonged QTc, although in some genetically proven cases of LQTS this prolongation can be hidden, known as concealed LQTS. The QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females.
Necrotizing sialometaplasia (NS) is a benign, ulcerative lesion, usually located towards the back of the hard palate. It is thought to be caused by ischemic necrosis (death of tissue due to lack of blood supply) of minor salivary glands in response to trauma. Often painless, the condition is self-limiting and should heal in 6–10 weeks. Although entirely benign and requiring no treatment, due to its similar appearance to oral cancer, it is sometimes misdiagnosed as malignant. Therefore, it is considered an important condition, despite its rarity. Signs and symptoms
The condition most commonly is located at the junction of the hard and soft palate. However, the condition may arise anywhere minor salivary glands are located. It has also been occasionally reported to involve the major salivary glands. It may be present only on one side, or both sides. The lesion typically is 1–4 cm in diameter.Initially, the lesion is a tender, erythematous (red) swelling. Later, in the ulcerated stage, the overlying mucosa breaks down to leave a deep, well-circumscribed ulcer which is yellow-gray in color and has a lobular base.There is usually only minor pain, and the condition is often entirely painless. There may be prodromal symptoms similar to flu before the appearance of the lesion. Causes
The exact cause of the condition is unknown. There is most evidence to support vascular infarction and ischemic necrosis of salivary gland lobules as a mechanism for the condition.