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The Institute for Cardiac RhythmsGlossary of cardiac rhythm terminologyAbnormal Sinus TachycardiaIf the heart races unexpectedly during rest, for example, an Abnormal Sinus Tachycardia could be occurring. This can cause palpitations (awareness of the heart's racing), fatigue or shortness of breath. Not necessarily dangerous in itself, Abnormal Sinus Tachycardia can however be a sign of some other problem. Accessory PathwayAn extra bridge between the atria and the ventricles found in less than 1% of the population. Also known as bypass tracts, they conduct impulses at faster speeds than the normal connects of the AVN. AtriaThe upper chambers of the heart. Atrial FibrillationAtrial electricity is nonstop. It twists and turns and excites different areas of the atria erratically, so the atrial muscle quivers rather than beats. Atrial FlutterA unique type of Supraventricular Tachycardia (SVT). The electrical impulse in the atria flows around and around in a continuous wave, repeatedly exciting and re-exciting the atria at rates of 300 beats per minute. The atrioventricular node usually filters out one-quarter to one-half of these impulses to keep the lower chambers at 75-150 beats per minute. Atrial TachycardiaAn abnormal, fast heart rhythm originating in the atria. A type of Supraventricular Tachycardia (SVT) that may be as fast as 200 beats per minute. Atrioventricular Node (AVN)A cluster of specialized cells at the floor of the right atrium near the center of the heart, that bridges the atria and ventricles electrically. It works as a filter to control how many and how quickly heartbeats reach the ventricle from the atria. Failure of the AVN can result in heart rates that are too fast or too slow. Heart blocks can also occur when the impulses do not pass through to the lower chambers. Atrioventricular Nodal Re-entrant Tachycardia (AVNRT)Supraventricular Tachycardias (SVT) that arise when the electrical impulse travels round and round in a continuous wave inside the AV Node. It can exit to the atria above and the ventricles below to cause heart rates of 130-180 beats per minute. Atrioventricular Re-entrant Tachycardia (AVRT)Supraventricular Tachycardias (SVT) that occur using an accessory pathway for the impulse to re-excite either the atria or the ventricles. BradycardiaA slow heart rate, usually less than 60 beats per minute. Not considered abnormal unless the slow heart rate is ineffective in bringing blood to the body's cells, and symptoms or inability to perform work occur. Some abnormal bradycardias include heart blocks where the impulse cannot travel from one part of the heart to another, or disease of the body's normal sinus pacemaker. In these cases, a pacemaker may be necessary. Bundle Branch BlockWhen one of the branches of the His-Purkinje System cannot carry the impulse normally. An electrical abnormality visible on an electrocardiogram, it may not have an impact on the heart's pumping or on its rhythms unless the block is complete and no impulses can reach the ventricles. CardioversionConverting one heart rhythm to another, usually from a rapid rhythm to a more controlled one. In most cases, it is done with electrical shock to the chest walls (external cardioversion). Internal cardioversions are accomplished with catheter electrodes placed within the heart's chambers. Medical cardioversions use strong drugs to affect the heart. Antitachycardia pacing uses pacemaker technology to convert rhythms. DefibrillationThe administration of an electrical shock to the heart to interrupt fibrillation (quivering of the muscle, rather than beating). A special type of cardioversion. Heart BlocksBlock of the impulse between or along the structures of the heart. AV Blocks limit the number of normal beats passing to the ventricles and reduce the heart rate. The block can be in the AVN, the His Bundle or, less commonly, in both the Bundle Branches. Often caused by damage to the heart following a heart attack but may be congenital. Some heart blocks require treatment with a pacemaker. His BundleA specialized group of cells leading from the AV Node and penetrating into the ventricles at the intraventricular septum. Named for Wilhelm His, Jr., this structure is an expressway to the network of fibers (Purkinje System) that bring the electrical spark to excite the ventricles. Failure of the His Bundle can cause heart block. Junctional TachycardiasSupraventricular Tachycardias (SVT) that are dependent upon bridges or connection at the junction, i.e., in the areas where the atria and ventricles meet. These bridges include the AV Node, His Bundle, and accessory pathways. Long QT SyndromeCongenital or acquired defects in the electrical recovery of the heart's cells can make the heart vulnerable to ventricular fibrillation (VF). In congenital Long QT Syndrome, stress, exercise, or being startled can trigger VF. Acquired Long QT Syndromes are incidental to some other issue or condition such as electrolyte imbalances from diuretics (water pills) and the eating disorder bulimia, from side effects of some medications such as Quinidine Sulfate, or use of street or illegal drugs like cocaine and aerosol propellants. Normal Sinus RhythmThe rate at which the heart beats as driven by the body's need to circulate blood; therefore, the rate is faster during activity or emotional stress than during sleep or relaxation. There can be some change even while at rest. PalpitationsAn awareness of irregular beats or variation in heart beat force. Several palpitations in a row are called flutters. Most palpitations involve premature beats even when felt as skipped beats because the heart has little time to fill and the force of the beat is diminished. The force and volume of the next normal beat is more than usual and, therefore, felt as a thump. Paroxysmal Atrial Tachycardia (PAT)An abnormal heart rhythm faster than 100 beats per minute originating in the atria that starts and stops frequently. Paroxysmal Junctional Re-entrant Tachycardia (PJRT)Another type of Supraventricular Tachycardia (SVT) involving an accessory pathway. It is often more persistent, sometimes even continuous. Premature BeatsA frequent and common occurrence. Extra or early beats from the atria are called atrial premature beats (APB), premature atrial beats (PAB), or premature atrial contraction (PAC). When the beat arises from the ventricles, it is called a ventricular premature beat (VPB), premature ventricular beat (PVB), or premature ventricular contraction (PVC). Purkinje SystemThe cells or bundles of cells that bring the impulse to the ventricular muscles. They branch to the right and left ventricles from the His Bundle. Sino-atrial Node (Sinus Node, SA Node)A cluster of specialized cells in the right atrium that spontaneously issues the impulse that spark normal heart beats. Sinus ArrhythmiaWhen the heart rate seems a bit irregular, speeding up or slowing down within normal ranges. Generally not considered abnormal. Sinus TachycardiaSinus rhythm that exceeds 100 beats per minute. It can be a normal physiologic response to exercise or fever. However, it may be abnormal if the body is not responding to these kinds of stresses. SyncopeA sudden collapse with loss of consciousness. It may be a brief blackout or faint with immediate recovery, or it may require treatment. Dizziness and lightheadedness may be forms of pre-syncope. Fainting, blackouts, or other loss of consciousness are never normal: they may be episodes of aborted Sudden Cardiac Death. TachycardiaHeart rates above 100 beats per minute are usually referred to as tachycardias. VentriclesThe lower chambers of the heart. Ventricular Fibrillation (VF)/ Sudden Cardiac Death (SCD)The lower chambers of the heart quiver as a result of chaotic electrical activity in the ventricles. The heart is no longer an effective pump and Sudden Cardiac Death or collapse occurs. Immediate defibrillation is required to prevent death. Ventricular Tachycardia (VT)Rapid heart rates arising from the lower chambers of the heart, VT is almost always more dangerous than any Supraventricular Tachycardia (atrial or junctional tachycardia) and it often precedes ventricular fibrillation. Recent research shows that people with nonsustained VT and history of heart attack are at risk for ventricular fibrillation. Wolff-Parkinson-White Syndrome (WPW)A condition where there is an accessory pathway detectable on a routine ECG (cardiogram) AND the patient has symptoms and tachycardias. The accessory pathway or bypass tract allows conduction or electrical flow to the ventricles faster than it would conduct over the normal path of AV Node and His Bundle. It reaches the ventricles first and causes pre-excitation. In some patients with WPW, atrial fibrillation can be particularly dangerous because the AV Node or filter is bypassed and the excessively rapid rates of atrial fibrillation can cause ventricular fibrillation (VF).
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