DISORDER OF HEART RHYTHM

 1. Etiology of heart rhythm disorder

2. Pathogenesis of heart rhythm disorder

3. Classification of heart rhythm disorders

4. Automatism violations

5. Conduction violations

6. Arrhythmias in the result of combined heart properties violations

 

Normally, heart work depends on normal automatism (conditions of driver sino-atrial node), excitability, conductive heart system condition and contractive myocardium properties. Arrhythmia is the condition, which is characterized by the violation of such heart physiological properties, as automatism, conduction of impulses through conductive ways, contractive myocardium properties by the violation of heart ability to learning of excitation rhythm, by the violation of frequency, rhythm or coordination of heart beats.

1. Etiology of heart rhythm disorder

The rhythm violations arise under the influence of different pathological agents, which can be divided on such groups:

1)     Functional violations and influences, for example: violation of vegetative nerves system condition (sympathetic or parasympathetic link hyperactivity), physical work, physical overload, body temperature changes, the increase of intracranium pressure, respiration (especially in children);

2)     Organic injury of myocardium, for example: inflammation of myocardium (as the result of infection), the myocardium dystrophy (in the result of hypoxia, ischemia or amiloidosis), necrosis of myocardium;

3)     Influences of toxic substances on the myocardium (alcohol, drugs, big dose adrenalin and noradrenalin, glucocorticoids, bacterial toxins, phosphororganic substances);

4)     Hormone balance disorder (hyperthyroidism, hypothyroidism,  hyperfunction  of  supranephral glands);

5)     Violation of intracellular or extracellular ions balance (changes of sodium, potassium, calcium, magnesium and chlorine concentration);

6)     Mechanical influences on the heart (catheter using for the diagnosis and treatment heart diseases, operation on the heart, chest trauma).

 

  2. Pathogenesis of heart rhythm disorder

         Ability to automatic impulses formation depends on pacemaker cells activity of the sinoatrial node, in which spontaneous slow depolarization of cells membrane takes place during diastole.  As the result, action membrane potential arises after achievement of some critical level (threshold level critical potential).  Impulses generation depends on maximum diastolic potential of these cells, on maximum diastolic potential measure, after which action membrane potential arises, and on speed of slow diastolic depolarization. The decrease of the threshold level maximum diastolic potential SA node p-cells or/and slow diastolic depolarization speed increase stimulates of the sinus tachycardia appearance at body temperature increase, in the result of sympathetic stimulation or withdrawal of vagal tone. On the contrary, decrease of speed slow spontaneous diastolic depolarization or/and increase threshold level critical potential and hyperpolarization in diastole causes the sinus bradycardia. Tone oscillations of n. Vagus at breathing time can induce the sinus respiratory arrhythmia (increase of hear beats during the inspiration). Respiratory arrhythmia in norm is in children, but now very often can be observed in adult.

Own automatism of lower part conductive heart system can appear in pathological conditions (arises so-called heterotopic or ectopic rhythm driver). That condition is the result of the automatism sinoatrial node ability decrement, so generation of the impulses arises in another myocardium conductive parts, new ectopic automatism driver appears. Beginning such automatism driver is the result damage of the different part conductive system, or electrical heterogeneous of myocardiocytes, or electrical unstable of myocardiocytes (especially in fourth phase action potential during formation of the resting membrane potential). In that cases extraordinary heart contractive or only ventricles arises (extrasystole). There are three mechanisms of the new ectopic rhythm driver appearance.

1. Appearance of the injured electricity in myocardium. It is the result of electrical heterogeneous myocardiocytes. So, between the uninjured myocardium (membrane charge is -90 mV membrane resting potential) and injured one (membrane is partly or totally depolarized, membrane charge, for example, is 0 mV or +20 mV) arises difference of the potential and it is the reason of the ectopic rhythm beginning.

2. Ectopic rhythm driver activation. It is the result of electrical  unstability  myocardiocytes and beginning in one case of the subthreshold level oscillations (unstable low amplitude oscillations of the resting membrane potential) and in other one - the beginning of overthreshold level oscillations (at the retardation or breaking of repolarization).

3. Re-entry mechanism. Under normal conditions, an electrical impulse is conducted through the heart in an orderly, sequential manner. The electrical impulse then dies out and does not reenter adjacent tissue because that tissue has already been depolarized and is refractory to immediate stimulation. However, under certain abnormal conditions, an impulse can reenter an area of myocardium that was previously depolarized and depolarize it again. There three conditions are the necessary for this mechanism beginning: 1 two conductive ways are the functionally or anatomically disconnected; 2 some conductive way is blocked; 3 the antegrade conductive way is blocked, but the retrograde one is preserved. So, in that condition impulse (or impulses) travels numerous through some area of conductive system and returns through another pathway to the reactivated myocardiocytes.

3. Classification of heart rhythm disorders

         The classification of heart arrhythmia types is based on the main heart properties violations.

1. Automatism violations. There are two groups of arrhythmias, which arise in the result of sinus-atrium node functional state violation. The first group is named nomotopic automatism violation and includes sinus tachycardia, sinus bradycardia and sinus arrhythmia. The second group is named heterotopic automatism violation and includes atrium-ventricular rhythm and idioventricular rhythm.

2. Conduction violations. There are two groups. The first group conduction violation unites block: sinus one, atrium one, atrium-ventricular one, ventricle one. The second group includes Wolf-Parkinson-White syndrome (pre-excitations syndrome).

3. Arrhythmias in the result of combined heart properties violations (automatism, conduction and excitability). This group unites extrasystole, paroxysmal tachycardia, atria flutter, ventricle flutter, atria fibrillation, and ventricle fibrillation.

4. Automatism violations

  Nomotopic (sinus node) rhythms.

    1.  Sinus tachycardia refers to a rapid heart rate (> 100 to 180 beats per minute) that has the origin in the SA node. The main reasons are physical or emotional stress, myocardial ischemia or infarction, myocardial dystrophy, congestive heart failure, fever, hyperthyroidism, pharmacological agents (atropine, isoproterenol, adrenalin), compensatory response to decreased cardiac output. ECG sings: all waves have normal configuration and priority, P wave and PR interval (0.12 to 0.20 second) precedes each QRS complex (sinus rhythm), all R-R are shortened.

2. Sinus bradycardia describes a slow heart rate (< 60 to 40 beats per minute) that has the origin in the SA node. It may be normal in trained athletes who maintain a large stroke volume, during sleep; in pathological condition after influenza or typhoid, intracranium pressure rise, irritation of the n. Vagus nucleases, may be an indicator of poor prognosis in patient with acute myocardial infarction that is associated with hypotension.  ECG sings: all waves have normal configuration and priority, normal P wave and PR interval precedes each QRS complex (sinus rhythm), all R-R are lengthened. This arrhythmia may cause heart output decrease and leads to cerebral or coronary blood flow insufficiency, in that condition ectopic pacemaker could be activated.

3. Sinus (respiratory) arrhythmia is characterized by gradually lengthening (at expiration) and shortening (at inspiration) R-R intervals and is the result of intrathoracic pressure changes during respiration. It is the normal for the children and can occur in adult after influenza, at neurocirculative dystone, hypertension, congestive heart failure, diabetes mellitus.  ECG sings: sinus rhythm, difference of all R-R is more than 0.15 second (at norm difference of all R-R is less than 0,15 sec).

Heterotopic rhythms. They are the result of ectopic automatism driver activation that is localized out SA node (for example, in atrium, in AV-node or in ventricle) because SA node failure (reasons - digitalis toxicity, myocardial infarction, acute myocarditis, excessive vagal tone, hyper- or hypokalemia). 

     1. Tardy ectopic rhythm (vicarious, passive) arises at the SA node arrest. ECG sings: heart beats not more 60 per minute. If ectopic pacemaker is localized in atrium on ECG inverted P wave is observed before QRS. If ectopic pacemaker is localized in AV node on ECG inverted P wave is observed after normal QRS, or hidden in QRS (atrial-ventricular rhythm). If ectopic pacemaker is localized in ventricle heart rate is less then 40 per minute, QRS is deformed (wide, distorted), it is so called idioventricular rhythm.

    2. Unparoxismal tachycardia begins and ends gradually, heart rate is 90 130/min. Ectopic driver may be localized in atrium, in AV node or in ventricle. So, complex PQRST has sings of nonsinus rhythm (alteration of configuration, duration and succession waves).

     3. Migration of supraventricular rhythm driver is characterized by the gradual removal of rhythm driver from SA node to AV one. ECG sings: violation of P wave configuration and lasting, dysrtythmia.

5. Conduction violations

Conduction violations include two groups of arrhythmias: heart block and pre-excitation syndrome and has the results from abnormality impulse conduction.

     Causes of heart block are conductive ways damage (myocardial infarction, myocarditis, cardiosclerosis, heart failure, coronary heart disease, vagal tone).  Conduction block can arise in the AV nodal fibers, in bungle of His, in the Purkinje conduction system, between SA node and atrium, inside atrium.

 1. Sinoatrial block has such sings: impulses are not transmitted out the SA node, so on ECG waves P, QRS, and T are absent, pause is equal 2 (R-R). Some time occurs sinus arrest and on ECG no 3 or 4 (sequence) cardiac complex, it may result irregular pulse, prolonged period of asystole.

2. Atrial block ECG sings: P waves are deformed and their duration is more than 0.11 second.

3. Atrium-ventricular block has three degree.

First-degree AV block is characterized only by the prolonged P-Q interval (< 0.2 second) in the result of retardation impulses conduction from atria to ventricles through AV node. Isolated first-degree AV block is never symptomatic.

Second-degree AV block is divided into two types. Type-first (Mobitz type I or Wenkebach phenomenon) is characterized by progressive lengthening of the PQ interval until an impulse is blocked, one cardiac cycle falls and then the cycle repeats again. After the fall of ventricle contraction -Q interval is restored, gradually becoming longer with each heart contraction. R-R are different, rhythm is irregular and there are more P waves than QRS complexes.

Type II (Mobitz type II) is usually associated with organic cardiac disease. It is the intermittent block of atrial impulses conduction with a constant PR interval (normal or long), but QRS complexes fall more frequently may be such correlations: 2:1; 3:1; 4:1. This type is complicated by cardiac output decrease.

Third-degree AV block, or complete AV block, occurs when the conduction link between the atria and ventricles is lost. The atria continue to beat at a normal rate and the ventricles develop their own rate, which normally is slow (30-40/min, idioventricular rhythm). The atria and ventricles rates are regular but dissociated (on ECG P waves and QRS complexes occur independently, count of P waves more than QRG. It causes periods of syncope, known as a Stokes-Adams attack (sings: asystole more than 10-20 sec, a decrease of cardiac output, insensibility, convulsions, is possible death).

4. Ventricle block. Interruption of impulse conduction through the bundle branches is called bundle branch block. These blocks usually do not cause alterations in the rhythm of the heartbeat.   Bundle branch block interrupts the normal progression of depolarization, causing the ventricles to depolarize one after the other because the impulses must travel through muscle tissue rather than through the specialized conductive tissue. It cause the QRS deformation, it is wide (normal is 0.08 to 0.12 second) and distorted. The left bundle branch bifurcates into left anterior and posterior fascicles. An interruption of one of these fascicles is referred to as a hemiblock. Their ECG sings are very difference, but the main sing is QRS complex deformation.

     Pre-excitation or Wolff-Parkinson-White (WPW) syndrome exists when atrial impulses are transmitted directly to the ventricles through shortcut conduction pathways. The impulses do not travel through the AV node but through accessory brunch (bungle of Kent). This connects the conduction system of the atria to either ventricle, bypassing the AV node. Impulses go down the accessory pathways and return by the normal conduction system to set up a re-entry system, it can cause supraventricular tachycardia. The ECG is characterized by a short P-R (less than 0.12 sec), a slurred upstoke on the QRS (delta wave), a wide QRS (more than 0.10 sec), secondary ST and T waves are changed (repolarization is altered). Another pre-excitation pattern is the Lown-Ganong-Levine syndrome, characterized by a short PR interval without a delta wave. These syndromes are dangerous because may cause electricity unstabilized myocardium, activation of ectopic driver and extrasistoles or paroxysmal ventricular tachycardia beginning.

6. Arrhythmias in the result of combined heart properties violations

Combined heart properties violations include disorders of automatism, conduction and irritability.

Extrasystole is the extraordinary systole in the result of ectopic pacemaker activation. New pacemaker (out sinus node) causes beginning excitation wave, which spreads in altered direction. Dependency on cell localization, where the extraordinary impulse is formed, distinguishes such types of extrasystole: sinus, atrial, atria-ventricular and ventricular.

Sinus extrasystole or premature atrial contraction is a beat initiated by an ectopic atrial focus that appears early in the cycle (before the next expected sinus beat). An excitation wave is usually conducted through the ventricular pathway in the normal manner not changes the shape of the QRS. A pause will follow the beat, and the SA node will start a new cycle. Atrial extrasystole is the result of ectopic pacemaker activation in different parts of atria. It is characterized by wave distortion (depressed, dysphasic, and negative) because excitation wave goes retrograde, by partial compensatory pause.

Atrial-ventricular extrasystole is observed at beginning ectopic pacemaker in AV node (top and middle part). Excitation wave spreads in two directions: in ventricles in normal, in atria in retrograde. So, wave is negative and indicates or after normal QRS complex or can be coincide with QRS. Ventricular extrasystole or premature ventricular contraction (it is caused by a ventricular ectopic pacemaker) is more dangerous than sinus or atrial because violates the pumping action of the heart. After such extrasystole the ventricle usually is not able torepolarise sufficiently to respond to the next impulse that arises in the SA node (compensatory pause arises), diastolic volume is usually insufficient for ejection of blood. On the ECG: extrasystole complex is registered early in the cycle, is not usually preceded by P wave, QRS is distorted and wide, large looping ST segment opposite in direction to that of the QRS, full compensatory pause (interval between the R waves before and after the extrasystole complex is twice that of the normal R-R).

Paroxysmal tachycardia. Extraordinary contractions can arise one by one or by groups. Paroxysmal tachycardia develops in case of numerous extrasystoles, with a rapid heart rate (in measure 140-250 beats per min, averaging about 170), which sudden onset and offset andcouses physiological rhythm break. Duration of paroxysm can be different from (some) seconds to (some) minutes, after that it similarly suddenly ends and adjusts normal rhythm.

Atrial paroxysmal tachycardia is mostly observed. The patient frequently complains of a sudden pounding or fluttering in the chest associated with weakness or breathlessness. The fast rate stresses then heart and increases its need for oxygen. The tachycardia may also diminish cardiac output because of shortened ventricular filling tame. The heart is beating so rapidly that the ventricle doesnt have time to fill completely, each beat pumps out less blood. If this tachycardia persists, the usual treatment is stimulation of the n.Vagus by carotid sinus or eyes massage, which slows the heart rate. Since this can produce dangerous slowing or cardiac arrest, the patient should be monitored.

Atrial flutter is a rapid and regular atrial ectopic tachycardia, with a rate that ranges from 240 to 450 beats per minute. There two types ofatrial flutter.

Type I flutter is the result of re-entry mechanism in the right atrium and the rate frequency may be 240-350/min.

The mechanism of type II is unknown. The atrial rate ranges between 350 and 450 beats in minute. On the ECG are defined regular and rapid F-waves (sawtooth pattern). Not all of the impulses are conduced, so the ventricular rate is usually slower. Because the impulses are coming so rapidly, the AV node cannot accept and conduct each one and ventricle response may be regular or irregular (some degree of block occurs at the node).

Atrial fibrillation is the result of chaotic current flow within the atria. When the atrial cells cannot repolarize in time for the next incoming stimulus, the ectopic current is rejected by the refractory cells and sent in another direction. On ECG: atrial electrical activity is disorganized and indicated by f-waves with frequency 350-700/min. Conduction through the AV node is disorganized, so complexes QRS appear irregular; the peripheral pulse is grossly irregular, and a pulse deficit can be observed.

Ventricle flutter (ventricular tachycardia) is the result of ventricle frequency excitement by permanently circulation impulses (re-entry mechanism). A rate usually is 150-200/min. On ECG: rate is fast, QRS is wide, and P waves may sometime be visible in the complex QRS. It is very dangerous arrhythmia because it leads to reduced cardiac output, and many times, to ventricular fibrillation.

In ventricular fibrillation, the ventricle quivers but doesnt contract, so there is no cardiac output, and there are no palpable or audible pulses. The classic ECG pattern of ventricular fibrillation is that of gross disorganization without identifiable waveforms or intervals (frequency 200-500/min) (fig. b).

Preventing more serious arrhythmias often involves drug therapy, electrical stimulation, or surgical intervention. The correction of very dangerous arrhythmias can involve the use of an electronic pacemaker, cardioversion, or defibrillation. Electrical interventions can be used in emergency and elective situations. A pacemaker is an electronic device that delivers an electrical stimulus to the heart. It is used to initiate heartbeats in situations when the normal pacemaker of the heart is defective or in complete heart block in which the rate of cardiac contraction and consequent cardiac output is inadequate to perfuse vital tissue. Overdrive pacing is used to treat recurrent ventricular tachycardia, atrial flutter. A pacemaker may be used as a temporary or a permanent measure.

Defibrillation and synchronized cardioversion are two reliable methods for treating ventricular tachycardia and fibrillation. The discharge of electrical energy that is synchronized with the R wave of the ECG is referred to as synchronized cardioversion, and unsynchronized discharge is known as defibrillation. The goal of both these techniques is to provide an electrical pulse to the heart in such a way as to completely depolarize the heart during passage of the current. This electrical current interrupts the disorganized impulses, allowing the SA node to regain control of the heart. Defibrillation depolarizes all of the myocardial cells simultaneously and allows the SA node to resume normal conduction.

The primary function of the heart is to supply blood and nutrients to the body. The regular beating, or contraction, of the heart moves the blood throughout the body. Each heartbeat is controlled by electrical impulses traveling through the heart. In the normal heart these electrical impulses occur in regular intervals. When something goes wrong with the hearts electrical system, the heart does not beat regularly. The irregular beating results in a rhythm disorder, or arrhythmia.

The electrical system regulating heartbeat consists of two main areas of control and a series of conducting pathways, similar to the electrical wiring in a house.

The sinoatrial, or SA, node is located in the right atrium. It is the source and main control and is the source of each heartbeat. The SA node responds to the body's overall need for blood and increases the heart rate when necessary, such as during exercise, emotional excitement, or illness such as fever. The SA node is sometimes called the "natural pacemaker" of the heart.

Electrical impulses leave the SA node and travel through special conducting pathways in the heart to the other area of control, theatrioventricular (AV) node. The AV node provides a pathway for impulses from the atria to the ventricles. It also creates a delay in conduction from the atria to the ventricle. This causes the atria to contract first and allow the ventricles to fill with blood before they contract themselves.

The delay ensures proper timing so that the lower chambers have time to fill completely before they contract.

Normally, the heart beats 60-100 times a minute. This state is called "normal sinus rhythm" or "normal rhythm." Depending upon the needs of the body, it may beat faster (sinus tachycardia) due to stress or slower (sinus bradycardia) such as during sleep.

Arrhythmias

Arrhythmias are abnormalities of the heartbeat. There are many types of arrhythmias, and they are classified by where they begin, (the atria, AV node, or the ventricles). Generally speaking, those that do not originate from the ventricles are called supraventricular arrhythmias while those that come from the ventricles are called ventricular arrhythmias.

The following are some of the more commonly encountered arrhythmias, starting with the supraventricular arrhythmias.

Premature atrial contractions (sometimes called PACs, APCs, or premature supraventricular contractions): PACs are an extra heart beat arising from the atria, outside of the SA node, that causes the heart to contract earlier than expected. This is a very common occurrence in all ages and usually is not serious.

Supraventricular tachycardia, or paroxysmal SVT: SVTs are regular, rapid heartbeats resulting from abnormal electrical impulses above the ventricle (usually the atria or the AV node).

Sick sinus syndrome: This syndrome is characterized by irregular firing of the SA node resulting in both slower and faster-than-normal heart rates.

Atrial fibrillation: A common condition caused by electrical impulses discharged at a rapid rate from many different areas of the atria. It usually causes a fast and irregular heartbeat.

Atrial flutter: A condition caused by a rapid discharge of abnormal electrical impulses from the right atrium. Typically, the right atrium fires at a rate of 300 beats per minute, but only every other beat is conducted through the AV node, meaning that the ventricular rate is classically 150 beats per minute.

Arrhythmias arising in the ventricle are more likely to be found in people with more serious heart disease but may also be found in healthy individuals.

Premature ventricular complex, or PVCs: This abnormal electrical impulse arises from the ventricle, causing the heart to beat earlier than expected. Usually, the heart returns to its normal rhythm right away.

Ventricular tachycardia: Fast and usually regular impulses come from the ventricles and cause a very rapid heart rate. This is usually a life-threatening tachycardia and needs immediate medical attention and potentially treatment with an electrical shock or defibrillation.

Ventricular fibrillation: Electrical impulses arise from the ventricles in a fast and disordered sequence. The resulting uncoordinated contractions cause the heart to lose its ability to beat and pump blood. The condition usually causes fainting and collapse, and is fatal if not treated immediately.

Arrhythmias can be frightening, but in many cases, especially in younger patients with normal underlying hearts, they are not life threatening and can be effectively treated with medications.

Supraventricular arrhythmias are very common in middle-aged and elderly adults. The older you get, the more likely you are to experience an arrhythmia, especially atrial fibrillation.

Many supraventricular arrhythmias are temporary and not serious, especially if no underlying heart disease is present. These arrhythmias are a response to normal activities or emotions.

Even if an arrhythmia has a serious underlying cause, the arrhythmia itself may not be dangerous. The underlying problem can often be treated effectively.

Heart Rhythm Disorders Causes

Among individuals without known heart disease, arrhythmias are generally random, isolated occurrences that do not carry any significance. However, a discussion with a doctor is advised.

A variety of heart diseases cause arrhythmias. Heart disease can refer to patients with coronary artery disease, heart valve problems, heart failure, or disorders with heart conduction or high blood pressure. Remember, however, that having an arrhythmia does not necessarily mean that you have heart disease. Arrhythmias have many causes; sometimes the cause of an arrhythmia is never determined.

Sometimes, conditions other than heart disease may cause or aggravate arrhythmias. These conditions include the following:

Infection or fever.

Physical or emotional stress.

Diseases such as anemia or thyroid disease.

Drugs and other stimulants, such as caffeine, tobacco, alcohol, cocaine, amphetamines, and certain over-the-counter and prescription medications.

Certain arrhythmias can be inherited as well.

Symptoms of a Heart Rhythm Disorders

Many arrhythmias cause no or minimal symptoms. Other people, however, can actually feel the arrhythmia when it happens.

Common symptoms include the following:

Palpitations, feeling "skipped beats"

Thumping or fluttering in the chest

Sensation of the heart racing

In addition, some can experience the following:

Feeling faint or tired

Light-headedness or passing out (syncope)

Shortness of breath

Chest pain or discomfort

On the other hand, people may feel many of the sensations described above and have no arrhythmias whatsoever. These may be due to anxiety, stress, or other causes besides an abnormal heartbeat.

When to Seek Medical Care for Your Heart Rhythm

Most people have noticed their heart racing, a fluttering in the chest, or a sensation that the heart skipped a beat. If this happens once, or infrequently, with no other symptoms, it is usually not serious. However, any questions or concerns should be discussed with a health care provider. The health care provider should also be notified if a recommended treatment does not alleviate the symptoms.

More serious symptoms should be evaluated immediately at the nearest hospital emergency department. These symptoms include:

Any unexplained shortness of breath

Light-headedness or feeling faint

Feeling that the heart is beating too slowly or too quickly

Chest pain with any of these symptoms

People experiencing these symptoms should not drive to the emergency department. They should call 9-1-1 for emergency medical transport.

Heart Rhythm Exams and Tests

Evaluation of heart rhythm disorders requires a discussion of symptoms and a physical exam with a health care provider.

In addition, an electrocardiogram (ECG) is mandatory to establish the exact type of arrhythmia. If the rhythm disturbance is present while the ECG is being recorded, the problem can be identified immediately. Otherwise, more specialized testing may be required. A 24-hour (or longer) recording of the heartbeat is often necessary to detect any rhythm problem that occurs daily but not constantly.

However, if the arrhythmia is even more infrequent, an event recorder may be used. These vary from hand-held machines that are activated by the patient whenever he or she feels symptoms, to some that are placed surgically under the skin and left there for up to one year.

An ultrasound of the heart, called an echocardiogram, is often used for an evaluation of the structure and function of the heart. In more serious cases, a test using electrodes placed inside the heart, called an electrophysiologic study (EPS), may be recommended to determine further management.

Treatment for Heart Rhythm Disorders

The treatment of heart rhythm disorders varies depending on the presence or absence of symptoms, how frequent the arrhythmia occurs, and the seriousness of any underlying heart condition. The treatment may range from medication to more advanced surgical procedures, such as an internal implanted cardiac defibrillator (ICD). Sometimes no treatment is necessary. At times, simple or specialized pacemakers may be required to control arrhythmias.

A detailed discussion of the tests and treatment options should be done with the health care provider.

Medications for Heart Rhythm Disorders

The choice and use of medications depends on the specific type of heart rhythm disorder you have. Detailed discussion about this is beyond the scope of this article.

Follow-Up for Heart Rhythm Disorders

Follow-up for a heart rhythm disorder is usually done with the primary care provider and often with a heart specialist. The patient is monitored for effectiveness of treatment, recurrence of symptoms or arrhythmia, side effects of medication, additional routine testing, and overall condition. For those requiring pacemakers, follow-up on a regular basis is mandatory.

The detection and management of heart rhythm disorders are undergoing constant improvement. The past few years have seen an unprecedented increase in understanding about these conditions. Detection and management of heart rhythm disorders has improved the quality and quantity of life.

Heart Rhythm Disorders Overview

The primary function of the heart is to supply blood and nutrients to the body. The regular beating, or contraction, of the heart moves the blood throughout the body. Each heartbeat is controlled by electrical impulses traveling through the heart. In the normal heart these electrical impulses occur in regular intervals. When something goes wrong with the heart's electrical system, the heart does not beat regularly. The irregular beating results in a rhythm disorder, or arrhythmia.

The electrical system regulating heartbeat consists of 2 main areas of control and a series of conducting pathways, similar to the electrical wiring in a house.

The sinoatrial, or SA, node is located in the right atrium. It provides the main control and is the source of each beat. The SA node also keeps up with the body's overall need for blood and increases the heart rate when necessary, such as during exercise, emotional excitement, or illness such as fever. The SA node is sometimes called the "natural pacemaker" of the heart.

Electrical impulses leave the SA node and travel through special conducting pathways in the heart to the other controller, the atrioventricular, or AV, node. The purpose of the AV node is to provide a pathway for impulses from the atriato the ventricles. It also creates a delay in conduction from the atria to theventricle. This causes the atria to contract first and allow the ventricles to fill with blood before they contract themselves.

The delay ensures proper timing so that the lower chambers have time to fill completely before they contract.

Normally, the heart beats 60-100 times a minute. This state is called "normal sinus rhythm" or "normal rhythm." Depending upon the needs of the body, it may beat faster (sinus tachycardia) due to stress or slower (sinus bradycardia) such as during sleep.

Arrhythmias

Arrhythmias are abnormalities of the heartbeat. There are many types of arrhythmias, and they are classified by where they begin, (the atria, AV node, or the ventricles). Generally speaking, those that do not originate from the ventricles are called supraventricular arrhythmias while those that come from the ventricles are called ventricular arrhythmias.

The following are some of the more commonly encountered arrhythmias, starting with the supraventricular arrhythmias.

Premature atrial contractions, sometimes called PAC or APC, or premature supraventricular contractions: Another part of the atria sends an electrical impulse soon after the previous beat, causing the heart to contract earlier than expected. This is a very common occurrence in all ages and usually is not serious.

Supraventricular tachycardia, or paroxysmal SVT: Occurs when any structure above the ventricle (usually the atria or the AV node) produces a regular, rapid discharge.

Sick sinus syndrome: Irregular firing by the SA node causes a slower-than-normal heart rate (sometimes alternating with rapid heart rates).

Atrial fibrillation: A common condition caused by electrical impulses discharged at a rapid rate from many different areas of the atria. It usually causes a fast and irregular heartbeat.

Atrial flutter: A condition caused by a rapid discharge from a single place in the right atrium. Typically, the right atrium fires at a rate of 300 beats per minute, but only every other beat is conducted through the AV node, meaning that the ventricular rate is classically 150 beats per minute.