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The secret pathways of cardiac electrical current: Why do abnormal signals bypass the atria and ventricles?
After heart surgery, patients may experience a rare heart syndrome called junctional ectopic tachycardia (JET), an abnormal heart rhythm caused by abnormal conduction in the heart. Symptoms of this condition, called congenital JET, or Hersch's bundle tachycardia, often develop within 24 to 48 hours of surgery.
PathophysiologyUnder normal circumstances, the electrical activity of the heart is initiated by the sinoatrial node (SA node) located in the right atrium, then propagates to the atrioventricular node (AV node), and then reaches the ventricles through the His bundle. The AV node acts as a gatekeeper of electrical activity, limiting the electrical signals that enter the ventricles. This function is critical to preventing the spread of rapid electrical activity in the atria to the ventricles. For example, in atrial fibrillation or atrial flutter, if the atria are activated at a rate of 300 beats per minute, the AV node will block some of the signal from reaching the ventricles, ultimately causing the ventricles to activate at 150 beats per minute.
A "short circuit" had developed in his heart, with the electrical current bypassing the AV node, causing the heart to beat abnormally fast.
Diagnosis
JET is usually diagnosed using a 12-lead electrocardiogram (ECG). Such an EKG shows a rapid, regular ventricular rate, usually between 170 and 260 beats per minute. The QRS complex is usually narrow but may be widened in the presence of bundle branch block. If the AV node is unable to conduct signals from the ventricles to the atria, electrocardiographic dissociation of atrial and ventricular activity may occur.
TreatmentJET can be distinguished from other forms of supraventricular tachycardia by the response of adenosine to which it results in a temporary loss of atrial conduction, whereas AVNRT is usually terminated.
Treatment of JET aims to lower the heart rate by correcting acidosis and electrolyte imbalances (particularly magnesium and calcium), cooling the patient, and using antiarrhythmic drugs. Occasionally pacing the atria at a rate higher than the JET may help improve cardiac function, allowing for coordinated action of the atria and ventricles. Drugs used to treat JET include beta-adrenergic blockers such as metoprolol, calcium channel blockers such as verapamil, and antiarrhythmic drugs such as flecainide and metoprolol.
EpidemiologyIn patients who experience multiple episodes of JET, catheter ablation is an alternative to long-term drug treatment by destroying small areas of the cells that initiate JET.
JET occurs primarily in children after heart surgery. The incidence varies among different types of surgery, ranging from approximately 2% to 22%, with a higher incidence after surgery to repair tetralogy of Fallot and a lower incidence after surgery to repair ventricular septal defect and arterial transposition. Low.
Etymology
The name conjunctive ectopic tachycardia refers to the problem it causes. The associativity comes from the fact that the abnormal tissue that drives the ventricular rate is located at the junction of the atria and ventricles, the AV node. Ectopic (from the Greek ektopos, meaning "not somewhere") occurs when the ventricles are triggered by tissue that is not the normal pacemaking tissue. And tachycardia (from the Greek words for "fast" and "heart") means a condition in which the heart beats at an abnormal rate.
It can be seen that combined ectopic tachycardia is an abnormal heart rhythm caused by abnormal discharge of cells near the AV node inside the heart. Does this mean that some structure of the heart remains hidden, affecting the rhythm of our heartbeat?
