Defibrillators, Implantable: Implantable devices which continuously monitor the electrical activity of the heart and automatically detect and terminate ventricular tachycardia (TACHYCARDIA, VENTRICULAR) and VENTRICULAR FIBRILLATION. They consist of an impulse generator, batteries, and electrodes.Defibrillators: Cardiac electrical stimulators that apply brief high-voltage electroshocks to the HEART. These stimulators are used to restore normal rhythm and contractile function in hearts of patients who are experiencing VENTRICULAR FIBRILLATION or ventricular tachycardia (TACHYCARDIA, VENTRICULAR) that is not accompanied by a palpable PULSE. Some defibrillators may also be used to correct certain noncritical dysrhythmias (called synchronized defibrillation or CARDIOVERSION), using relatively low-level discharges synchronized to the patient's ECG waveform. (UMDNS, 2003)Electric Countershock: An electrical current applied to the HEART to terminate a disturbance of its rhythm, ARRHYTHMIAS, CARDIAC. (Stedman, 25th ed)Tachycardia, Ventricular: An abnormally rapid ventricular rhythm usually in excess of 150 beats per minute. It is generated within the ventricle below the BUNDLE OF HIS, either as autonomic impulse formation or reentrant impulse conduction. Depending on the etiology, onset of ventricular tachycardia can be paroxysmal (sudden) or nonparoxysmal, its wide QRS complexes can be uniform or polymorphic, and the ventricular beating may be independent of the atrial beating (AV dissociation).Ventricular Fibrillation: A potentially lethal cardiac arrhythmia that is characterized by uncoordinated extremely rapid firing of electrical impulses (400-600/min) in HEART VENTRICLES. Such asynchronous ventricular quivering or fibrillation prevents any effective cardiac output and results in unconsciousness (SYNCOPE). It is one of the major electrocardiographic patterns seen with CARDIAC ARREST.Equipment Failure: Failure of equipment to perform to standard. The failure may be due to defects or improper use.Death, Sudden, Cardiac: Unexpected rapid natural death due to cardiovascular collapse within one hour of initial symptoms. It is usually caused by the worsening of existing heart diseases. The sudden onset of symptoms, such as CHEST PAIN and CARDIAC ARRHYTHMIAS, particularly VENTRICULAR TACHYCARDIA, can lead to the loss of consciousness and cardiac arrest followed by biological death. (from Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7th ed., 2005)Arrhythmias, Cardiac: Any disturbances of the normal rhythmic beating of the heart or MYOCARDIAL CONTRACTION. Cardiac arrhythmias can be classified by the abnormalities in HEART RATE, disorders of electrical impulse generation, or impulse conduction.Pacemaker, Artificial: A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external).Heart Arrest: Cessation of heart beat or MYOCARDIAL CONTRACTION. If it is treated within a few minutes, heart arrest can be reversed in most cases to normal cardiac rhythm and effective circulation.Electric Injuries: Injuries caused by electric currents. The concept excludes electric burns (BURNS, ELECTRIC), but includes accidental electrocution and electric shock.Equipment Safety: Freedom of equipment from actual or potential hazards.Electrodes, Implanted: Surgically placed electric conductors through which ELECTRIC STIMULATION is delivered to or electrical activity is recorded from a specific point inside the body.Device Removal: Removal of an implanted therapeutic or prosthetic device.Implantable Neurostimulators: Surgically placed electric conductors through which ELECTRIC STIMULATION of nerve tissue is delivered.Anti-Arrhythmia Agents: Agents used for the treatment or prevention of cardiac arrhythmias. They may affect the polarization-repolarization phase of the action potential, its excitability or refractoriness, or impulse conduction or membrane responsiveness within cardiac fibers. Anti-arrhythmia agents are often classed into four main groups according to their mechanism of action: sodium channel blockade, beta-adrenergic blockade, repolarization prolongation, or calcium channel blockade.Equipment Design: Methods of creating machines and devices.Cardiac Resynchronization Therapy: The restoration of the sequential order of contraction and relaxation of the HEART ATRIA and HEART VENTRICLES by atrio-biventricular pacing.Electrocardiography: Recording of the moment-to-moment electromotive forces of the HEART as projected onto various sites on the body's surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a CATHODE RAY TUBE DISPLAY.Amiodarone: An antianginal and class III antiarrhythmic drug. It increases the duration of ventricular and atrial muscle action by inhibiting POTASSIUM CHANNELS and VOLTAGE-GATED SODIUM CHANNELS. There is a resulting decrease in heart rate and in vascular resistance.Prostheses and Implants: Artificial substitutes for body parts, and materials inserted into tissue for functional, cosmetic, or therapeutic purposes. Prostheses can be functional, as in the case of artificial arms and legs, or cosmetic, as in the case of an artificial eye. Implants, all surgically inserted or grafted into the body, tend to be used therapeutically. IMPLANTS, EXPERIMENTAL is available for those used experimentally.Cardiac Pacing, Artificial: Regulation of the rate of contraction of the heart muscles by an artificial pacemaker.Equipment Failure Analysis: The evaluation of incidents involving the loss of function of a device. These evaluations are used for a variety of purposes such as to determine the failure rates, the causes of failures, costs of failures, and the reliability and maintainability of devices.Syncope: A transient loss of consciousness and postural tone caused by diminished blood flow to the brain (i.e., BRAIN ISCHEMIA). Presyncope refers to the sensation of lightheadedness and loss of strength that precedes a syncopal event or accompanies an incomplete syncope. (From Adams et al., Principles of Neurology, 6th ed, pp367-9)Prosthesis Implantation: Surgical insertion of a prosthesis.Cardiopulmonary Resuscitation: The artificial substitution of heart and lung action as indicated for HEART ARREST resulting from electric shock, DROWNING, respiratory arrest, or other causes. The two major components of cardiopulmonary resuscitation are artificial ventilation (RESPIRATION, ARTIFICIAL) and closed-chest CARDIAC MASSAGE.Treatment Outcome: Evaluation undertaken to assess the results or consequences of management and procedures used in combating disease in order to determine the efficacy, effectiveness, safety, and practicability of these interventions in individual cases or series.Heart Failure: A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (VENTRICULAR DYSFUNCTION), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as MYOCARDIAL INFARCTION.Cardiac Resynchronization Therapy Devices: Types of artificial pacemakers with implantable leads to be placed at multiple intracardial sites. They are used to treat various cardiac conduction disturbances which interfere with the timing of contraction of the ventricles. They may or may not include defibrillating electrodes (IMPLANTABLE DEFIBRILLATORS) as well.Infusion Pumps, Implantable: Implanted fluid propulsion systems with self-contained power source for providing long-term controlled-rate delivery of drugs such as chemotherapeutic agents or analgesics. Delivery rate may be externally controlled or osmotically or peristatically controlled with the aid of transcutaneous monitoring.Follow-Up Studies: Studies in which individuals or populations are followed to assess the outcome of exposures, procedures, or effects of a characteristic, e.g., occurrence of disease.Tachycardia: Abnormally rapid heartbeat, usually with a HEART RATE above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia.Telemetry: Transmission of the readings of instruments to a remote location by means of wires, radio waves, or other means. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Electrophysiologic Techniques, Cardiac: Methods to induce and measure electrical activities at specific sites in the heart to diagnose and treat problems with the heart's electrical system.Electrocardiography, Ambulatory: Method in which prolonged electrocardiographic recordings are made on a portable tape recorder (Holter-type system) or solid-state device ("real-time" system), while the patient undergoes normal daily activities. It is useful in the diagnosis and management of intermittent cardiac arrhythmias and transient myocardial ischemia.Out-of-Hospital Cardiac Arrest: Occurrence of heart arrest in an individual when there is no immediate access to medical personnel or equipment.Ventricular Dysfunction, Left: A condition in which the LEFT VENTRICLE of the heart was functionally impaired. This condition usually leads to HEART FAILURE; MYOCARDIAL INFARCTION; and other cardiovascular complications. Diagnosis is made by measuring the diminished ejection fraction and a depressed level of motility of the left ventricular wall.Stroke Volume: The amount of BLOOD pumped out of the HEART per beat, not to be confused with cardiac output (volume/time). It is calculated as the difference between the end-diastolic volume and the end-systolic volume.Brugada Syndrome: An autosomal dominant defect of cardiac conduction that is characterized by an abnormal ST-segment in leads V1-V3 on the ELECTROCARDIOGRAM resembling a right BUNDLE-BRANCH BLOCK; high risk of VENTRICULAR TACHYCARDIA; or VENTRICULAR FIBRILLATION; SYNCOPAL EPISODE; and possible sudden death. This syndrome is linked to mutations of gene encoding the cardiac SODIUM CHANNEL alpha subunit.Cardiomyopathies: A group of diseases in which the dominant feature is the involvement of the CARDIAC MUSCLE itself. Cardiomyopathies are classified according to their predominant pathophysiological features (DILATED CARDIOMYOPATHY; HYPERTROPHIC CARDIOMYOPATHY; RESTRICTIVE CARDIOMYOPATHY) or their etiological/pathological factors (CARDIOMYOPATHY, ALCOHOLIC; ENDOCARDIAL FIBROELASTOSIS).Electromagnetic Phenomena: Characteristics of ELECTRICITY and magnetism such as charged particles and the properties and behavior of charged particles, and other phenomena related to or associated with electromagnetism.Prospective Studies: Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.Tachycardia, Supraventricular: A generic expression for any tachycardia that originates above the BUNDLE OF HIS.Primary Prevention: Specific practices for the prevention of disease or mental disorders in susceptible individuals or populations. These include HEALTH PROMOTION, including mental health; protective procedures, such as COMMUNICABLE DISEASE CONTROL; and monitoring and regulation of ENVIRONMENTAL POLLUTANTS. Primary prevention is to be distinguished from SECONDARY PREVENTION and TERTIARY PREVENTION.Risk Assessment: The qualitative or quantitative estimation of the likelihood of adverse effects that may result from exposure to specified health hazards or from the absence of beneficial influences. (Last, Dictionary of Epidemiology, 1988)Remote Sensing Technology: Observation and acquisition of physical data from a distance by viewing and making measurements from a distance or receiving transmitted data from observations made at distant location.Retrospective Studies: Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.Death, Sudden: The abrupt cessation of all vital bodily functions, manifested by the permanent loss of total cerebral, respiratory, and cardiovascular functions.Cardiac Electrophysiology: The study of the electrical activity and characteristics of the HEART; MYOCARDIUM; and CARDIOMYOCYTES.Atrial Fibrillation: Abnormal cardiac rhythm that is characterized by rapid, uncoordinated firing of electrical impulses in the upper chambers of the heart (HEART ATRIA). In such case, blood cannot be effectively pumped into the lower chambers of the heart (HEART VENTRICLES). It is caused by abnormal impulse generation.Cardiography, Impedance: A type of impedance plethysmography in which bioelectrical impedance is measured between electrodes positioned around the neck and around the lower thorax. It is used principally to calculate stroke volume and cardiac volume, but it is also related to myocardial contractility, thoracic fluid content, and circulation to the extremities.Time Factors: Elements of limited time intervals, contributing to particular results or situations.Heart-Assist Devices: Small pumps, often implantable, designed for temporarily assisting the heart, usually the LEFT VENTRICLE, to pump blood. They consist of a pumping chamber and a power source, which may be partially or totally external to the body and activated by electromagnetic motors.Survival Rate: The proportion of survivors in a group, e.g., of patients, studied and followed over a period, or the proportion of persons in a specified group alive at the beginning of a time interval who survive to the end of the interval. It is often studied using life table methods.Cardiomyopathy, Dilated: A form of CARDIAC MUSCLE disease that is characterized by ventricular dilation, VENTRICULAR DYSFUNCTION, and HEART FAILURE. Risk factors include SMOKING; ALCOHOL DRINKING; HYPERTENSION; INFECTION; PREGNANCY; and mutations in the LMNA gene encoding LAMIN TYPE A, a NUCLEAR LAMINA protein.Monitoring, Ambulatory: The use of electronic equipment to observe or record physiologic processes while the patient undergoes normal daily activities.Volunteers: Persons who donate their services.Risk Factors: An aspect of personal behavior or lifestyle, environmental exposure, or inborn or inherited characteristic, which, on the basis of epidemiologic evidence, is known to be associated with a health-related condition considered important to prevent.Survival Analysis: A class of statistical procedures for estimating the survival function (function of time, starting with a population 100% well at a given time and providing the percentage of the population still well at later times). The survival analysis is then used for making inferences about the effects of treatments, prognostic factors, exposures, and other covariates on the function.Therapy, Computer-Assisted: Computer systems utilized as adjuncts in the treatment of disease.Arrhythmogenic Right Ventricular Dysplasia: A congenital cardiomyopathy that is characterized by infiltration of adipose and fibrous tissue into the RIGHT VENTRICLE wall and loss of myocardial cells. Primary injuries usually are at the free wall of right ventricular and right atria resulting in ventricular and supraventricular arrhythmias.Magnets: Objects that produce a magnetic field.Electric Power Supplies: Devices that control the supply of electric current for running electrical equipment.Emergency Medical Services: Services specifically designed, staffed, and equipped for the emergency care of patients.Kaplan-Meier Estimate: A nonparametric method of compiling LIFE TABLES or survival tables. It combines calculated probabilities of survival and estimates to allow for observations occurring beyond a measurement threshold, which are assumed to occur randomly. Time intervals are defined as ending each time an event occurs and are therefore unequal. (From Last, A Dictionary of Epidemiology, 1995)Cost-Benefit Analysis: A method of comparing the cost of a program with its expected benefits in dollars (or other currency). The benefit-to-cost ratio is a measure of total return expected per unit of money spent. This analysis generally excludes consideration of factors that are not measured ultimately in economic terms. Cost effectiveness compares alternative ways to achieve a specific set of results.Sotalol: An adrenergic beta-antagonist that is used in the treatment of life-threatening arrhythmias.Neural Prostheses: Medical devices which substitute for a nervous system function by electrically stimulating the nerves directly and monitoring the response to the electrical stimulation.Prosthesis-Related Infections: Infections resulting from the implantation of prosthetic devices. The infections may be acquired from intraoperative contamination (early) or hematogenously acquired from other sites (late).Burns, Electric: Burns produced by contact with electric current or from a sudden discharge of electricity.Radio Frequency Identification Device: Machine readable patient or equipment identification device using radio frequency from 125 kHz to 5.8 Ghz.Amplifiers, Electronic: Electronic devices that increase the magnitude of a signal's power level or current.Tachycardia, Sinus: Simple rapid heartbeats caused by rapid discharge of impulses from the SINOATRIAL NODE, usually between 100 and 180 beats/min in adults. It is characterized by a gradual onset and termination. Sinus tachycardia is common in infants, young children, and adults during strenuous physical activities.Recurrence: The return of a sign, symptom, or disease after a remission.Equipment and Supplies: Expendable and nonexpendable equipment, supplies, apparatus, and instruments that are used in diagnostic, surgical, therapeutic, scientific, and experimental procedures.Ventricular Dysfunction: A condition in which HEART VENTRICLES exhibit impaired function.Bundle-Branch Block: A form of heart block in which the electrical stimulation of HEART VENTRICLES is interrupted at either one of the branches of BUNDLE OF HIS thus preventing the simultaneous depolarization of the two ventricles.Unnecessary Procedures: Diagnostic, therapeutic, and investigative procedures prescribed and performed by health professionals, the results of which do not justify the benefits or hazards and costs to the patient.Resuscitation: The restoration to life or consciousness of one apparently dead. (Dorland, 27th ed)Adrenergic beta-Antagonists: Drugs that bind to but do not activate beta-adrenergic receptors thereby blocking the actions of beta-adrenergic agonists. Adrenergic beta-antagonists are used for treatment of hypertension, cardiac arrhythmias, angina pectoris, glaucoma, migraine headaches, and anxiety.Registries: The systems and processes involved in the establishment, support, management, and operation of registers, e.g., disease registers.Cardiomyopathy, Hypertrophic: A form of CARDIAC MUSCLE disease, characterized by left and/or right ventricular hypertrophy (HYPERTROPHY, LEFT VENTRICULAR; HYPERTROPHY, RIGHT VENTRICULAR), frequent asymmetrical involvement of the HEART SEPTUM, and normal or reduced left ventricular volume. Risk factors include HYPERTENSION; AORTIC STENOSIS; and gene MUTATION; (FAMILIAL HYPERTROPHIC CARDIOMYOPATHY).Electric Stimulation Therapy: Application of electric current in treatment without the generation of perceptible heat. It includes electric stimulation of nerves or muscles, passage of current into the body, or use of interrupted current of low intensity to raise the threshold of the skin to pain.Monitoring, Physiologic: The continuous measurement of physiological processes, blood pressure, heart rate, renal output, reflexes, respiration, etc., in a patient or experimental animal; includes pharmacologic monitoring, the measurement of administered drugs or their metabolites in the blood, tissues, or urine.Secondary Prevention: The prevention of recurrences or exacerbations of a disease or complications of its therapy.Heart Diseases: Pathological conditions involving the HEART including its structural and functional abnormalities.Telemedicine: Delivery of health services via remote telecommunications. This includes interactive consultative and diagnostic services.First Aid: Emergency care or treatment given to a person who suddenly becomes ill or injured before full medical services become available.Subclavian Vein: The continuation of the axillary vein which follows the subclavian artery and then joins the internal jugular vein to form the brachiocephalic vein.Heart Conduction System: An impulse-conducting system composed of modified cardiac muscle, having the power of spontaneous rhythmicity and conduction more highly developed than the rest of the heart.Feasibility Studies: Studies to determine the advantages or disadvantages, practicability, or capability of accomplishing a projected plan, study, or project.Incidence: The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from PREVALENCE, which refers to all cases, new or old, in the population at a given time.Differential Threshold: The smallest difference which can be discriminated between two stimuli or one which is barely above the threshold.Emergency Treatment: First aid or other immediate intervention for accidents or medical conditions requiring immediate care and treatment before definitive medical and surgical management can be procured.Cicatrix: The fibrous tissue that replaces normal tissue during the process of WOUND HEALING.Proportional Hazards Models: Statistical models used in survival analysis that assert that the effect of the study factors on the hazard rate in the study population is multiplicative and does not change over time.Aircraft: A weight-carrying structure for navigation of the air that is supported either by its own buoyancy or by the dynamic action of the air against its surfaces. (Webster, 1973)Catheter Ablation: Removal of tissue with electrical current delivered via electrodes positioned at the distal end of a catheter. Energy sources are commonly direct current (DC-shock) or alternating current at radiofrequencies (usually 750 kHz). The technique is used most often to ablate the AV junction and/or accessory pathways in order to interrupt AV conduction and produce AV block in the treatment of various tachyarrhythmias.Myocardial Ischemia: A disorder of cardiac function caused by insufficient blood flow to the muscle tissue of the heart. The decreased blood flow may be due to narrowing of the coronary arteries (CORONARY ARTERY DISEASE), to obstruction by a thrombus (CORONARY THROMBOSIS), or less commonly, to diffuse narrowing of arterioles and other small vessels within the heart. Severe interruption of the blood supply to the myocardial tissue may result in necrosis of cardiac muscle (MYOCARDIAL INFARCTION).Prosthesis Failure: Malfunction of implantation shunts, valves, etc., and prosthesis loosening, migration, and breaking.Heart Ventricles: The lower right and left chambers of the heart. The right ventricle pumps venous BLOOD into the LUNGS and the left ventricle pumps oxygenated blood into the systemic arterial circulation.Prosthesis Design: The plan and delineation of prostheses in general or a specific prosthesis.Catheters, Indwelling: Catheters designed to be left within an organ or passage for an extended period of time.Axillary Vein: The venous trunk of the upper limb; a continuation of the basilar and brachial veins running from the lower border of the teres major muscle to the outer border of the first rib where it becomes the subclavian vein.Myocardial Infarction: NECROSIS of the MYOCARDIUM caused by an obstruction of the blood supply to the heart (CORONARY CIRCULATION).Patient Selection: Criteria and standards used for the determination of the appropriateness of the inclusion of patients with specific conditions in proposed treatment plans and the criteria used for the inclusion of subjects in various clinical trials and other research protocols.Commotio Cordis: A sudden CARDIAC ARRHYTHMIA (e.g., VENTRICULAR FIBRILLATION) caused by a blunt, non-penetrating impact to the precordial region of chest wall. Commotio cordis often results in sudden death without prompt cardiopulmonary defibrillation.Emergency Medical Tags: A bracelet or necklace worn by an individual that alerts emergency personnel of medical information for that individual which could affect their condition or treatment.Algorithms: A procedure consisting of a sequence of algebraic formulas and/or logical steps to calculate or determine a given task.Remote Consultation: Consultation via remote telecommunications, generally for the purpose of diagnosis or treatment of a patient at a site remote from the patient or primary physician.Electromagnetic Fields: Fields representing the joint interplay of electric and magnetic forces.Predictive Value of Tests: In screening and diagnostic tests, the probability that a person with a positive test is a true positive (i.e., has the disease), is referred to as the predictive value of a positive test; whereas, the predictive value of a negative test is the probability that the person with a negative test does not have the disease. Predictive value is related to the sensitivity and specificity of the test.Biomedical Enhancement: The use of technology-based interventions to improve functional capacities rather than to treat disease.Multicenter Studies as Topic: Works about controlled studies which are planned and carried out by several cooperating institutions to assess certain variables and outcomes in specific patient populations, for example, a multicenter study of congenital anomalies in children.Diagnosis, Computer-Assisted: Application of computer programs designed to assist the physician in solving a diagnostic problem.Randomized Controlled Trials as Topic: Works about clinical trials that involve at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table.Foreign-Body Migration: Migration of a foreign body from its original location to some other location in the body.Electrodes: Electric conductors through which electric currents enter or leave a medium, whether it be an electrolytic solution, solid, molten mass, gas, or vacuum.Endpoint Determination: Establishment of the level of a quantifiable effect indicative of a biologic process. The evaluation is frequently to detect the degree of toxic or therapeutic effect.Wireless Technology: Techniques using energy such as radio frequency, infrared light, laser light, visible light, or acoustic energy to transfer information without the use of wires, over both short and long distances.Videodisc Recording: The storing of visual and usually sound signals on discs for later reproduction on a television screen or monitor.Ventricular Function, Left: The hemodynamic and electrophysiological action of the left HEART VENTRICLE. Its measurement is an important aspect of the clinical evaluation of patients with heart disease to determine the effects of the disease on cardiac performance.Pacific States: The geographic designation for states bordering on or located in the Pacific Ocean. The states so designated are Alaska, California, Hawaii, Oregon, and Washington. (U.S. Geologic Survey telephone communication)Emergency Medical Technicians: Paramedical personnel trained to provide basic emergency care and life support under the supervision of physicians and/or nurses. These services may be carried out at the site of the emergency, in the ambulance, or in a health care institution.United StatesHeart Rate: The number of times the HEART VENTRICLES contract per unit of time, usually per minute.Coronary Sinus: A short vein that collects about two thirds of the venous blood from the MYOCARDIUM and drains into the RIGHT ATRIUM. Coronary sinus, normally located between the LEFT ATRIUM and LEFT VENTRICLE on the posterior surface of the heart, can serve as an anatomical reference for cardiac procedures.Health ResortsCardiology: The study of the heart, its physiology, and its functions.Heart Massage: Rhythmic compression of the heart by pressure applied manually over the sternum (closed heart massage) or directly to the heart through an opening in the chest wall (open heart massage). It is done to reinstate and maintain circulation. (Dorland, 28th ed)Chi-Square Distribution: A distribution in which a variable is distributed like the sum of the squares of any given independent random variable, each of which has a normal distribution with mean of zero and variance of one. The chi-square test is a statistical test based on comparison of a test statistic to a chi-square distribution. The oldest of these tests are used to detect whether two or more population distributions differ from one another.Ambulances: A vehicle equipped for transporting patients in need of emergency care.Miniaturization: The design or construction of objects greatly reduced in scale.Bradycardia: Cardiac arrhythmias that are characterized by excessively slow HEART RATE, usually below 50 beats per minute in human adults. They can be classified broadly into SINOATRIAL NODE dysfunction and ATRIOVENTRICULAR BLOCK.Diagnostic Techniques, Cardiovascular: Methods and procedures for the diagnosis of diseases or dysfunction of the cardiovascular system or its organs or demonstration of their physiological processes.Micro-Electrical-Mechanical Systems: A class of devices combining electrical and mechanical components that have at least one of the dimensions in the micrometer range (between 1 micron and 1 millimeter). They include sensors, actuators, microducts, and micropumps.Prognosis: A prediction of the probable outcome of a disease based on a individual's condition and the usual course of the disease as seen in similar situations.Electricity: The physical effects involving the presence of electric charges at rest and in motion.Heart Transplantation: The transference of a heart from one human or animal to another.Sick Sinus Syndrome: A condition caused by dysfunctions related to the SINOATRIAL NODE including impulse generation (CARDIAC SINUS ARREST) and impulse conduction (SINOATRIAL EXIT BLOCK). It is characterized by persistent BRADYCARDIA, chronic ATRIAL FIBRILLATION, and failure to resume sinus rhythm following CARDIOVERSION. This syndrome can be congenital or acquired, particularly after surgical correction for heart defects.Endocardium: The innermost layer of the heart, comprised of endothelial cells.Combined Modality Therapy: The treatment of a disease or condition by several different means simultaneously or sequentially. Chemoimmunotherapy, RADIOIMMUNOTHERAPY, chemoradiotherapy, cryochemotherapy, and SALVAGE THERAPY are seen most frequently, but their combinations with each other and surgery are also used.EuropeSignal Processing, Computer-Assisted: Computer-assisted processing of electric, ultrasonic, or electronic signals to interpret function and activity.Pectoralis Muscles: The pectoralis major and pectoralis minor muscles that make up the upper and fore part of the chest in front of the AXILLA.Practice Guidelines as Topic: Directions or principles presenting current or future rules of policy for assisting health care practitioners in patient care decisions regarding diagnosis, therapy, or related clinical circumstances. The guidelines may be developed by government agencies at any level, institutions, professional societies, governing boards, or by the convening of expert panels. The guidelines form a basis for the evaluation of all aspects of health care and delivery.Cause of Death: Factors which produce cessation of all vital bodily functions. They can be analyzed from an epidemiologic viewpoint.Laser Therapy: The use of photothermal effects of LASERS to coagulate, incise, vaporize, resect, dissect, or resurface tissue.Sensitivity and Specificity: Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition. (From Last, Dictionary of Epidemiology, 2d ed)Quality of Life: A generic concept reflecting concern with the modification and enhancement of life attributes, e.g., physical, political, moral and social environment; the overall condition of a human life.Cardiovascular Agents: Agents that affect the rate or intensity of cardiac contraction, blood vessel diameter, or blood volume.Echocardiography: Ultrasonic recording of the size, motion, and composition of the heart and surrounding tissues. The standard approach is transthoracic.Atrioventricular Block: Impaired impulse conduction from HEART ATRIA to HEART VENTRICLES. AV block can mean delayed or completely blocked impulse conduction.GermanyAnxiety: Feeling or emotion of dread, apprehension, and impending disaster but not disabling as with ANXIETY DISORDERS.Manifest Anxiety Scale: True-false questionnaire made up of items believed to indicate anxiety, in which the subject answers verbally the statement that describes him.Multivariate Analysis: A set of techniques used when variation in several variables has to be studied simultaneously. In statistics, multivariate analysis is interpreted as any analytic method that allows simultaneous study of two or more dependent variables.Implants, Experimental: Artificial substitutes for body parts and materials inserted into organisms during experimental studies.Long QT Syndrome: A condition that is characterized by episodes of fainting (SYNCOPE) and varying degree of ventricular arrhythmia as indicated by the prolonged QT interval. The inherited forms are caused by mutation of genes encoding cardiac ion channel proteins. The two major forms are ROMANO-WARD SYNDROME and JERVELL-LANGE NIELSEN SYNDROME.Evaluation Studies as Topic: Studies determining the effectiveness or value of processes, personnel, and equipment, or the material on conducting such studies. For drugs and devices, CLINICAL TRIALS AS TOPIC; DRUG EVALUATION; and DRUG EVALUATION, PRECLINICAL are available.Automobile Driving: The effect of environmental or physiological factors on the driver and driving ability. Included are driving fatigue, and the effect of drugs, disease, and physical disabilities on driving.Accelerated Idioventricular Rhythm: A type of automatic, not reentrant, ectopic ventricular rhythm with episodes lasting from a few seconds to a minute which usually occurs in patients with acute myocardial infarction or with DIGITALIS toxicity. The ventricular rate is faster than normal but slower than tachycardia, with an upper limit of 100 -120 beats per minute. Suppressive therapy is rarely necessary.Life Tables: Summarizing techniques used to describe the pattern of mortality and survival in populations. These methods can be applied to the study not only of death, but also of any defined endpoint such as the onset of disease or the occurrence of disease complications.Heart Injuries: General or unspecified injuries to the heart.Cohort Studies: Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.Risk: The probability that an event will occur. It encompasses a variety of measures of the probability of a generally unfavorable outcome.American Heart Association: A voluntary organization concerned with the prevention and treatment of heart and vascular diseases.Imidazolidines: Compounds based on reduced IMIDAZOLINES which contain no double bonds in the ring.Body Surface Potential Mapping: Recording of regional electrophysiological information by analysis of surface potentials to give a complete picture of the effects of the currents from the heart on the body surface. It has been applied to the diagnosis of old inferior myocardial infarction, localization of the bypass pathway in Wolff-Parkinson-White syndrome, recognition of ventricular hypertrophy, estimation of the size of a myocardial infarct, and the effects of different interventions designed to reduce infarct size. The limiting factor at present is the complexity of the recording and analysis, which requires 100 or more electrodes, sophisticated instrumentation, and dedicated personnel. (Braunwald, Heart Disease, 4th ed)Phlebography: Radiographic visualization or recording of a vein after the injection of contrast medium.Reproducibility of Results: The statistical reproducibility of measurements (often in a clinical context), including the testing of instrumentation or techniques to obtain reproducible results. The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results.Biocompatible Materials: Synthetic or natural materials, other than DRUGS, that are used to replace or repair any body TISSUES or bodily function.Heart Block: Impaired conduction of cardiac impulse that can occur anywhere along the conduction pathway, such as between the SINOATRIAL NODE and the right atrium (SA block) or between atria and ventricles (AV block). Heart blocks can be classified by the duration, frequency, or completeness of conduction block. Reversibility depends on the degree of structural or functional defects.Catheterization, Central Venous: Placement of an intravenous CATHETER in the subclavian, jugular, or other central vein.Hospitalization: The confinement of a patient in a hospital.Product Surveillance, Postmarketing: Surveillance of drugs, devices, appliances, etc., for efficacy or adverse effects, after they have been released for general sale.Severity of Illness Index: Levels within a diagnostic group which are established by various measurement criteria applied to the seriousness of a patient's disorder.