Definition

Any deviation in or departure from the normal sinus mechanism.

History

Symptoms: The patient may be asymptomatic or present with palpitations, dyspnea, lethargy, weakness, dizziness, chest pain, syncope, congestive heart failure (CHF), or complete hemodynamic collapse.

General:Frequently, dysrhythmias occur as a complication of an underlying illness thus making a thorough review of symptoms essential.

Age: Usually Occur after the fifth decade of life but may be seen in conjunction with a congenital abnormality.

Onset: Acute, paroxysmal, or asymptomatic.

Pulmonary: Assess adequacy of ventilation and oxygenation. Auscultate for evidence of CHF.

Duration: Extremely variable; may last for a few seconds, hours, or days.

Intensity: Variable.

Aggravating Factors:Emotional stress, caffeine, cigarette smoking,ETOH intake, physical activity, and certain pharmacologic agents.

Alleviating Factors: If relief occurs, it is usually spontaneous.

Associated Factors: Coronary artery and pulmonary disease. Congenital abnormalities.

Physical Examination

General: The physical examination rarely yields a definitive diagnosis, but reveals the degree of hemodynamic compromise thereby guiding the intensity and urgency of treatment. A complete and thorough examination is indicated as it may provide evidence of underlying disease that is necessary for appropriate and effective treatment.

Cardiovascular:

Blood pressure (check for orthostasis and paradox) may be elevated, decreased, or absent. Tachypnea or bradypnea, elevated or decreased temperature may be seen, and arterial pulses may be present or absent. The rate may increase or decrease and the rhythm may be regular, irregular, or regularly irregular.

Assessment of the jugular venous pulsation may provide clues as to atrial activity.

Assessment of jugular venous distention may provide clues as to volume status.

Precordial inspection and palpation for lifts, heaves, and dyskinetic areas. Locate and assess apical impulse for enlargement and lateral displacement. These signs may indicate cardiomegaly. Percussion of cardiac border may also provide evidence of cardiomegaly.

Cardiac auscultation: Volume of Sj and Sz may be diminished in cases of pericardial effusion and chronic obstructive pulmonary disease (COPD). S3 gallop may be present with CHF. S4 gallop may be present with heart block or atrial flutter. Murmurs must be characterized in relation to possible valvular lesions.

Pathophysiology

Atrial Rhythms

Normal Sinus Rhythm

Normal sinus rhythm describes a regular, narrow complex rhythm that originates at the sinus node with a rate of 60 to 100 bpm. P waves must be upright in leads II, III, and a Vf. The P-R interval must be between 0.12 and 0.20 seconds for sinus rhythm to be diagnosed

Sinus tachycardia is diagnosed when the normal sinus mechanism is present and the rate exceeds 100 bpm.Sinus bradycardia is present when the normal sinus mechanism is present and the rate falls below 60 bpm .

Premature Atrial Contractions

Premature atrial contractions (PACs) are early atrial depolarizations originating at a focus other than the sinus node. P waves may differ in morphology and axis from normal sinus. These beats are usually conducted producing a normal P-R interval .

Supraventricular Tachycardia

The term supraventricular tachycardia (SVT) describes a myriad of non sinus tachycardias originating in the atria or atrioventricular (A V) node. SVT may arise as a result of accelerated automaticity or it may be the result of a reentrant circuit involving the A V node, a by pass tract, or even the sinus node.

SVTs are generally regular and range from 150 to 240 bpm. P waves may be of nonsinus configuration or axis (P waves negative in leads II, III, and aVt). P waves generally precede the QRS by a normal or shortened P-R interval. P waves may also follow the QRS as a result of late retrograde depolarization of the atria these are known as retrograde P waves. Conduction is usually in the ratio of 1: 1, but at atrial rates greater than 200 bpm block may occur. The QRS is narrow and of normal configuration; however, aberrancy or bundle branch block may occur. In these situations where the QRS is widened or atrial activity difficult to identify, differentiation from ventricular tachycardia (VT) may be extremely difficult.

Atrial Flutter

In atrial flutter the atrial rate varies between 250 and 350 bpm producing the characteristic sawtooth flutter waves. Ventricular rate depends on the degree of A V block present, a 2: 1 ratio is most common in the untreated individual. The P-R interval is usually constant and of normal length but may be short. The QRS is narrow but aberration may occur In situations where the flutter waves are not readily apparent and atrial flutter must be differentiated from SVT, carotid sinus massage may usually conducted normally producing a normal P-R interval.

Atrial Fibrillation

Atrial fibrillation (AF) is a chaotic atrial rhythm in which no organized atrial activity is evident on the electrocardiogram (ECG). Ventricular response is irregularly irregular ranging from 160 to 180 bpm. The QRS is usually narrow but aberration frequently occurs.

Ventricular Dysrhythmias

Premature Ventricular Contractions

A premature ventricular contraction (PVC) occurs when the ventricles are depolarized before the next expected sinus beat. As the impulse propagates through the myocardium it does not utilize the normal conduction system, therefore the resulting complex is wide (> 0.12 sec) and bizzare in shape. Because of its ventricular origin it is not related to the normal sinus chain of events and occurs randomly, producing an irregular rhythm. PVCs may occur singly or in couplets. They may occur at regular intervals, for example, every second (bigeminy) or third (trigeminy) beat. PVCs may arise from a single focus (unifocal) or multiple foci (multifocal) .

Ventricular Tachycardia

Ventricular tachycardia (VT) is a wide QRS tachycardia arising in the ventricle. The rate may range from 100 to 250 bpm. The rhythm is regular and if atrial activity is identifiable, A V dissociation is present. At times it may be very difficult to distinguish VT from SVT with aberrancy. The following criteria, if identifiable, favor VT .

1. QRS greater than 0.14 seconds.

2. Left axis deviation .

3. AV dissociation is present.

4. A monophasic or biphasic right bundle pattern is present in lead .

Ventricular Fibrillation

Ventricular fibrillation (VF) is a chaotic ventricular rhythm in which there is no organized complex on the ECG. It may appear as fine or coarse. VF is always a medical emergency because there is no cardiac output generated by this rhythm .

Atrioventricular Block

First Degree Atrioventricular Block

First degree A V block occurs when conduction of the atrial impulse to the ventricle is delayed at the A V node. On the ECG this appears as a prolonged P-R inteernal, by definition greater than 0.20 seconds. Otherwise the ECG 1S normal .

Second Degree Atrioventricular Block: Type I and Type II

Type I or Wenkebach is characterized by a sequentially lengthening P-R interval until complete block occurs and no QRS is conducted. The cycle then usually repeats itself. The atrial rhythm is regular, but because of variable conduction the ventricular rate is regularly irregular. QRS complexes are normal .

Type II ultimately results in intermittent complete block, but without lengthening the P-R interval. The atrial rhythm is regular as is the ventricular rhythm, but due to the regular complete block the ventricular rate is less than the atrial rate. The P-R interval and QRS of conducted beats are normal.

Third Degree Atrioventricular Block Third degree AV block describes complete block of electrical communication between the atria and the ventricles. The atrial rate and rhythm are regular. If a ventricular or junctional escape rhythm develops, its timing has no relationship to atrial electrical activity.

Diagnostic Studies

Laboratory

Serum electrolytes: To evaluate for abnormalities especially potassium, magnesium, and calcium. Cardiac enzymes (creatinine phosphokinase, lactic dehydrogenase, serum glutamicoxaloacetic transaminase (SGOT): Elevate elevated cardiac enzymes with elevated isoenzymes screens for myocardial infarction.

Thyroid function tests:To rule out hyperthyroidism or hypothyroidism.

Toxicology and therapeutic drug levels:To rule out poisoning, illicit drug use, or toxic levels as an etiology.

Arterial blood gasses: Rule out hypoxemia or acid base disturbances.

Radiology

Chest X-ray film (CXR): Rule out cardiomegaly, CHF, or primary pulmonary disease.

Cardiac catheterization: Variable findings and limited in scope of assessing cardiac function and underlying disorder. Useful in assessing coronary disease, left ventricular function, valvular and subvalvular anatomy, and intracardiac shunts.

Ventilation perfusion (V /0) scan of lung: Rule out pulmonary embolus.

Other

Holter monitoring:

Useful for documenting paroxysmal or infrequently occurring dysrhythmias. Also provides a recorded copy of the rhythm necessary for diagnosis.

Exercise treadmill testing: May precipitate exercise induced dysrhythmias or reveal myocardial ischemia.

12 Lead ECG: Most useful if obtained during dysrhythmic episode, but may reveal underlying conduction abnormalities known to be associated with certain dysrhythmias or may reveal signs of other cardiac disease (e.g., ischemia, chamber hypertrophy, pericarditis).

Signal average ECG: In patients with cardiomyopathy or recent myocardial infarction, the signal average ECG detects minute electrical variations that are known to be associated with malignant ventricular dysrhythmias.

Echocardiogram: Useful in assessing chamber size, wall-thickness, myocardial contractility, valvular function, and presence of pericardial fluid; all of which in varying combinations are useful in identifying any number of cardiac maladies.

Endomyocardial biopsy: If inflammatory or infiltrative disease is suspected.

Electrophysiology studies (EPS): Indicated in any ventricular dysrhythmia and any atrial dysrhythmia not easily explained by a correctable cause. EPS provide detailed information about the origin of the rhythm, hence guiding therapy and also providing a test of instituted therapy.

Differential Diagnosis

Traumatic

After surgery: History of cardiac surgery.

Traumatic cardiac contusion: History of chest wall injury; may have chest pain that is musculoskeletal or pericarditic in nature. ECG may show changes of myocardial injury.

Infectious

Myocarditis (viral, fungal, parasitic): An inflammatory process involving the myocardium. May present as simple upper respiratory infection and is associated with new nonspecific ECG changes, pericarditis, or dysrhythmia alone. Often may be undiagnosed and may result in dilated cardiomyopathy.

Metabolic

Electrolyte abnormality of any etiology: Frequently asymptomatic except for rhythm disturbance. Hypokalemia/hypomagnesemia most frequently associated with diuretic use and may produce simple uncompli cated PACs/PVCs if mild to AF or VT is severe. Hyperkalemia and hypermagnesemia most frequently associated with renal failure (acute or chronic) and may lead to bradydysrhythmias or high-degree AV block.

Hyperthyroidism:

AF with or without CHF may be the presenting complaint in thyrotoxicity.

Chronic obstructive pulmonary disease: Primary presenting symptom is dyspnea and bronchospasm. Dysrhythmias most commonly associated with advanced cases resulting in cor pulmonale or acute exacerbations resulting in acute hypoxia.

Cardiomyopathy (dilated, restrictive, infiltrative): The most common presentation of cardiomyopathy is CHF.

Valvular disease:Presentation varies depending on the valve involved, although discussion is found in later sections.

Neoplastic: Primary or metastatic tumors may interfere with valvular or conduction system function leading to any number of rhythm disturbances. Presentation is extremely variable but most closely associated to its location and attendant mechanical interruption of normal function.

Vascular

Pulmonary emboli (without production of mechanical heart failure): Chest pain, frequently pleuritic. Dyspnea paroxysmal and may not be relieved by any maneuvers. May have hemoptysis and fever. Frequent evidence of deep venous thrombosis. CXR normal or revealing wedged-shaped segmental density(ies).

Coronary artery disease: Myocardial ischemia or infarction are probably the most common etiologic agents of cardiac dysrhythmias. A thorough discussion of these entities can be found in later sections.

Congenital: Any structural abnormality may predispose to dysrhythmia.

Acquired

Drug toxicity: Many drugs have potential cardiac side effects. The most common offenders are the cardiac drugs themselves, but other medications such as tricyclic antidepressants and non sedating antihistamines (Seldane, Hismanal) may be arrhythmogenic. Illicit drugs must also be considered, especially stimulants like cocaine and methamphetamine preparations.

Idiopathic:These are situations where there appears to be no underlying etiology. Presentation is frequently the rhythm and its attendant symptoms. The most common example is SVT in a young athlete or paroxysmal atrial tachycardia in a normal individual.

Arrhythmias Treatment

Always: Correctly identify the rhythm, correct any underlying abnormalities, and let clinical stability guide aggressiveness and timeliness of therapy. Acutely, atrial tachydysrhythmias require ventricular rate control, usually with AV node blocking drugs, such as digitalis (1.0 to 1.5-mg loading dose followed by 0.125 to 0.375-mg/d, dependent on age, lean body weight, and primarily renal function) or calcium channel blockers, such as diltiazem (60- to 360-mgld in divided doses three or four times a day; dosage is titrated to effect). Diltiazem is also available intravenously and is bolused 0.25 mg/kg over 2 minutes and followed by a continuous infusion of 5 to 15-mg/h, titrated to effect). Once rate is controlled and the patient is stable, conversion to sinus rhythm may be undertaken electively, either chemically (quinidine-gluconate 200 to 400mg every 6 hours or glucuronate 324 to 628-mg every 8 to 12 hours, OR procainamide 250-to 1000 mg/d every 3 hours or sustained release every 6 hours; 50 mg/min intravenously up to 1000 mg then maintenance infusion of 2to 6mg/min) or electrically with direct current cardioversion. If any sign of hemodynamic instability is present, direct current cardioversion (by Advanced Cardiac Life Support protocols) must be considered first line therapy.

Maintenance therapy mayor may not be necessary depending on the etiology of the rhythm. In cases where conversion to sinus is not possible or maintenance of sinus is unlikely, chronic rate control is the goal. Conversely, in bradydysrhythmias, the goal is to raise the effective ventricular rate either chemically (atropine, 0.5- to 1.0-mg IVP maximum of 2.0 mg) or electrically with pacing. In chronic conditions medication is of no benefit and permanent pacing must be considered. For the most part, ventricular tachydysrhythmias are medical emergencies and require immediate intervention.

Pediatric Considerations

Atrial: PACs Occur in healthy children, as welI as those experiencing digitalis, toxicity, or those having undergone cardiac surgery. In children,isolated PACs generally do not cause symptoms and do not require treatment. SVT is the most Commonly occurring tachyarrhythmia in children. SVT is most often idiopathic with an estimated 10 to 20 percent of cases due to underlying Wolff-Parkinson-White syndrome. If there is no hemodynamic compromise (CHF, chest pain, lightheadedness, syncope), then vagal stimulating maneuvers (carotid sinus massage, gagging, standing on head) are often effective and should be attempted first. For infants with hemodynamic compromise, conversion to sinus rhythm can often be achieved by momentarily placing a bag of ice over the infant’s face to stimulate the diving reflex. For children with hemodynamic compromise, direct current synchronized cardioversion is the initial treatment of choice.

Atrial flutter Occurs in children with heart disease resulting in an enlarged atria (e.g., mitraVtricuspid valve disease). It is also seen as a sequelae of atrial surgery. Atrial flutter may Occur in children with structurally normal hearts, a high index of suspicion needs to be maintained for underlying cardiac disease. Treatment is always indicated in children. AF is an uncommon arrhythmia in children. Most often occurs in the presence of enlarged atria or after atrial surgery. May occur in conjunction with Wolff-Parkinson-White syndrome. Sick sinus syndrome and complete heart block occur in children as a result of cardiac surgery, myocarditis, in association with congenital heart defects, and idiopathically. An infant whose mother has systemic lupus erythematosus is at increased risk for congenital complete heart block. Treatment is dependent on the patient’s symptoms and ranges from pharmacologic intervention to the placement of a permanent pacemaker.

Ventricular:

PVCs may occur in children with structurally normal hearts and should be considered a normal finding if they are uniform and are supressed by exercise. Other common causes of PVCs include myocarditis, congenital heart disease, cardiac surgeries, and drug toxicities. Additional evaluation should be conducted in children who have multiform PVCs, multiple PVCs (e.g., couplets, triplets, etc.), or PVCs that increase in frequency or are induced by exercise. VT in children is generally associated with prior cardiac surgery. Other causes include cardiomyopathy, long Q-T syndrome, myocardial tumors, and drug toxicities. It is generally agreed that asymptomatic patients with structurally normal hearts do not require treatment. Patients with altered hemodynamics require aggressive treatment.

VF is caused by the same factors as VT. It is a medical emergency that requires immediate treatment. If the child becomes unconscious, direct current synchronized cardioversion is the treatment of choice. For the conscious child, pharmacologic treatment should begin immediately.

Obstetrical Considerations

The most common types of arrhythmias seen in pregnancy are the various kinds of tachycardias. Where treatment of arrhythmias is indicated, most of the antiarrhythmic medications and electrical cardioversion can be used without danger to the fetus. One exception in the drug phenytoin, which is sometimes used for treatment of paroxysmal atrial flutter or AF,supraventricular and ventricular arrhythmias, which are due to digitalis. Phenytoin is well known for causing congenital malformations.

Another medication that is contraindicated during pregnancy is warfarin sodium (coumadin). This drug has resulted in the “warfarin syndrome” (nasal hypoplasia, epiphyseal stippling, bilateral optic atrophy, scoliosis, mental retardation), other fetal central nervous system anomalies, spontaneous abortion, stillbirths, prematurity, and hemorrhage. If anticoagulation is indicated during the treatment of arrhythmias, the drug of choice in a pregnant patient is heparin. When heparin is in use, however, there is an increased risk of maternal hemorrhage associated with the last trimester and the postpartum period. In regards to specific arrhythmias, pregnancy in patients with AV block is well tolerated if there are no other cardiac problems; alternatively, AF associated with valvular heart disease can be dangerous to both the mother and the fetus.

Tagged under:arrhythmias arrhythmias disease arrhythmias treatment cardiac arrhythmias cardiac surgery Cardiology heart arrhythmias ventricular arrhythmias

Share This

Filed under: Cardiology