However, when a PVC occurs the impulse nearly always travels through only one bundle fiber, so there is no neutralization effect; this results in the high voltage QRS wave in the electrocardiograph. There are three main physiological explanations for premature ventricular contractions: enhanced ectopic nodal automaticity, re-entry signaling, and toxic/reperfusion triggered. Ectopic enhanced nodal automaticity suggests foci of sub-pulmonic valvular pacemaker cells that have a subthreshold potential for firing. The basic rhythm of the heart raises these cells to threshold, which precipitates an ectopic beat. This process is the underlying mechanism for arrhythmias due to excess catecholamines and some electrolyte deficiencies, particularly low blood potassium, known as hypokalemia. Reentry occurs when an area of 1-way block in the Purkinje fibers and a second area of slow conduction are present. This condition is frequently seen in patients with underlying heart disease that creates areas of differential conduction and recovery due to myocardial scarring or ischemia. During ventricular activation, one bundle tracts area of slow conduction activates the other tracts bundle fibers post block after the rest of the ventricle has recovered. This resulting in an extra beat. Reentry can produce single ectopic beats, or it can trigger paroxysmal tachycardia. Triggered beats are considered to be due to after-depolarizations triggered by the preceding action potential. These are often seen in patients with ventricular arrhythmias due to digoxin toxicity and reperfusion therapy after myocardial infarction (MI).
Histopathology
In case an ovarian cyst is surgically removed, a more definite diagnosis can be made by histopathology:

Treatment
Cysts associated with hypothyroidism or other endocrine problems are managed by treating the underlying condition. About 95% of ovarian cysts are benign, not cancerous. Functional cysts and hemorrhagic ovarian cysts usually resolve spontaneously. However, the bigger an ovarian cyst is, the less likely it is to disappear on its own. Treatment may be required if cysts persist over several months, grow, or cause increasing pain. Cysts that persist beyond two or three menstrual cycles, or occur in post-menopausal women, may indicate more serious disease and should be investigated through ultrasonography and laparoscopy, especially in cases where family members have had ovarian cancer. Such cysts may require surgical biopsy. Additionally, a blood test may be taken before surgery to check for elevated CA-125, a tumour marker, which is often found in increased levels in ovarian cancer, although it can also be elevated by other conditions resulting in a large number of false positives. Pain
Pain associated with ovarian cysts may be treated in several ways:

Pain relievers such as acetaminophen, nonsteroidal anti-inflammatory drugs, or opioids. While hormonal birth control prevents the development of new cysts in those who frequently get them, it is not useful for the treatment of current cysts. Surgery
Although most cases of ovarian cysts involve monitoring, some cases require surgery. This may involve removing the cyst, or one or both ovaries. Technique is typically laparoscopic, unless the cyst is particularly large, or if pre-operative imaging suggests malignancy or complex anatomy.