Cardiovascular Study Guide for the CCRN

Dysrhythmias

Dysrhythmias occur when the heart beats abnormally as a result of internal or external factors. Electrocardiograms (ECG) are used to trace the activity of the heart and help define normal rates from abnormal ones. ECGs have a variety of settings.

Diagnosis

The most common and conventional test is a 12-lead ECG, in which 10 electrodes are placed in various spots among the extremities and chest to trace these electrical impulses. Below is a list of dysrhythmias the nurse may encounter in practice. Please use your nursing texts to visualize lead placement in the 12-lead ECG and arrhythmia tracings, as you will need to know this for future testing purposes.

Types of Dysrhythmia

Sinus Bradycardia— Sinus bradycardia is classified by a decreased rate of heartbeat impulses. It has normal P waves and QRS complexes but occur at a rate of <50-60 beats per minute. It may be considered a normal condition, especially for athletes, older adults, and during sleep. Medications such as calcium channel blockers and beta-blockers, increased cranial pressure, and recent myocardial infarction may result in bradycardia. If acute and symptomatic, atropine 0.5-1 mg IV may be given.

Sinus Tachycardia— Sinus tachycardia is classified by an increase in impulse frequency. The P waves, QRS, and T waves are usually normal in shape, though the QRS and T waves may overlap. The whole complex may be irregular as well. The patient will have a rapid pulse and may experience hypotension, dizziness, and pulmonary edema. Causes of this condition include acute volume loss (blood, shock, etc.), hypovolemic heart failure, fever, infection, anxiety, exercise, and some medications. Calcium channel blockers and beta-blockers help to reduce heart rate.

Supraventricular Tachycardia— Supraventricular tachycardia (SVT) is defined as >100 beats per minute. At times, SVT ranges from 200-300 beats per minute. This may decrease heart function and cause congestive heart failure. In this rhythm, there is some overlap between the P and preceding T waves, though the QRS complex appears normal. Treatment for SVT includes adenosine, digoxin, verapamil, vagal maneuvers, and cardioversion. In some cases, cardiac ablation may be required.

Wolff-Parkinson-White— Wolff-Parkinson-White syndrome is a type of congenital supraventricular tachycardia. In this condition, infants are born with an extra electrical pathway that extends between the atria and ventricles without necessarily passing through the AV node. Conduction of a cardiac rhythm through this pathway can cause tachycardia and short circuits. This condition, while present at birth, may not be symptomatic until late adolescence or early adulthood.

Sinus Arrhythmia— Sinus arrhythmia is often a paradoxical heart rhythm in which heart impulse increases with inspiration and decreases with expiration due to the altering stimulation of the vagus nerve. This arrhythmia is most often noticed when the nurse palpates the pulse fluctuations. This arrhythmia is most prevalent in children and young adults and tends to decrease with age. The P waves and QRS complexes are generally normal with this condition, just the rate and rhythm are mildly irregular. Treatment may be indicated if this rhythm occurs with bradycardia.

Premature Atrial Contractions— Premature Atrial Contractions (PAC) are extra atrial impulses that act as extra beats or palpitations. On ECG tracing, the nurse will see extra P waves, a normal to slightly abnormal QRS complex, and irregular rhythm. It can be caused by caffeine, nicotine, alcohol, increased fluid volume, decreased potassium levels, metabolic conditions, atrial ischemia, or myocardial infarction. Patients may experience palpitations with this condition. If the PACs occur greater than six episodes per hour or with severe palpitations, further testing is indicated.

Atrial Flutter— Atrial flutter is characterized by a fast atrial rate, usually 250-400 beats per minute with or without excessive ventricular activity (general rates 75-150 beats per minute). It may be caused by coronary artery disease, valvular disease, pulmonary disease, alcohol ingestion, and cardiac surgery. Symptoms of this condition include chest pain, difficulty breathing, and decreased blood pressure. If unstable, cardioversion may be implemented. Medications to help slow ventricular rate include non-dihydropyridine calcium channel blockers and beta-blockers. For converting back to sinus rhythm, Tikosyn® and amiodarone may be used.

Atrial Fibrillation— Atrial fibrillation is the constant, disorganized beating of the atrium which can cause decreased blood movement and blood clots. The patient may experience palpitations and fatigue as the ventricles try to compensate for the decreased stroke volume and overactivity of the atrum. The atrial rate may be 300-600 beats per minute, while the ventricular rate ranges from 120-200 beats per minute. Risk factors for acquiring and treatment of atrial fibrillation are the same as atrial flutter.

Premature Junctional Contractions— Junctional dysrhythmias arise from the dysfunction of the area around the AV node. Premature junctional contractions (PJC) is a premature impulse to the AV node prior to the normal sinus impulse. It is similar to premature atrial contractions (PAC); however, PJCs may be a sign of digoxin toxicity. In this rhythm, the QRS complex may come early and a P wave may or may not be present. The interval of the rhythm is usually regular and symptoms of this condition are rare.

Junctional Rhythms— Junctional rhythms are the result of the AV node taking over the role of initiating cardiac rhythm. Instead of sinus node impulse initiation, which occurs at 60-100 beats per minute, the atrial node dictates the pace at 40-60 beats per minute. The P wave may be absent or inverted but the QRS complex will appear normal. This rhythm may also be defined as the junctional escape rhythm and is a protective measure to prevent asystole with sinus node failure. Junctional tachycardia occurs when the junctional rate is greater than 100 beats per minute.

AV Nodal Reentry Tachycardia— AV nodal reentry tachycardia is also known as paroxysmal atrial tachycardia or supraventricular tachycardia. It occurs as impulses are sent quickly to both the AV node and ventricles. Atrial heart rate may be 150-250 whereas the ventricular rate is 75-250. P waves may be difficult to see and are small if present. The QRS complex is generally normal. Symptoms include chest pain, dyspnea, and hypotension. It may be corrected with vagal maneuvers, adenosine, verapamil, or diltiazem, and/or cardioversion.

Premature Ventricular Contractions— Premature ventricular contractions (PVC) occur when impulses begin in the ventricles during a beat cycle. The abnormal impulses cause an irregular QRS complex. Patients will also have an irregular heartbeat. PVCs can be caused by electrolyte imbalances, caffeine, nicotine, and alcohol. It may be a precursor to ventricular tachycardia, especially if there is a presence of more than six PVCs in one hour. Treatment measures include lidocaine, procainamide, and treating any underlying cause.

Ventricular Tachycardia— Ventricular tachycardia is the presence of greater than three PVCs in a row. This must coincide with a ventricular rhythm rate of 100-200 beats per minute. This rate of contraction disables the heart from pumping blood effectively. Patients with this condition may be unconscious without a palpable pulse. If a pulse is palpated, synchronized cardioversion and adenosine may be given to convert the rhythm back to normal. If a pulse is not palpated, emergency defibrillation, epinephrine, and amiodarone will be used to try to regain a normal rhythm.

Narrow Complex and Wide Complex Tachycardias— Narrow and wide complex tachycardias are classified by the width of the QRS complex. Wide complex tachycardia occurs when the QRS is >0.12 seconds and extra impulses are introduced below the AV node. The most common wide complex tachycardia is ventricular tachycardia. It may cause palpitations, difficulty breathing, diaphoresis, anxiety, and cardiac arrest. Narrow complex tachycardia, then, is defined by a QRS <0.12 seconds and is usually supraventricular in origin. It may additionally present with symptoms of peripheral edema.

Prolonged QT interval— Prolonged QT intervals can cause symptoms of increased and irregular heartbeats. It can be caused by genetic conditions, cardiac structure abnormalities, or certain medications. Symptoms of prolonged QT include syncope, chest palpitations, shortness of breath, and cardiac arrest with sudden death.

Ventricular Fibrillation— Ventricular fibrillation is a rapid, irregular beating (often greater than >300 beats per minute) of the ventricles without atrial input. There are no recognizable P waves or QRS complexes. This is a pulseless rhythm and will result in death if not immediately treated. Emergency defibrillation followed by IV push epinephrine 1 mg every 3-5 minutes and amiodarone 300 mg (first dose) and 150 mg (second dose).

Idioventricular Rhythm— Idioventricular rhythms occur when the Purkinje fibers create impulses due to sinus node failure or AV node blockage. The rate will be regular between 20-40 beats per minute. The tracing of this rate shows an absent P wave and an abnormally shaped QRS complex. A patient in this rhythm may lose consciousness.

Ventricular Asystole— Ventricular asystole or asystole is the absence of heart activity. It is also known as cardiac arrest. There may be an occasional beat, known as an “escape beat” or “agonal rhythm”. CPR with mechanical airway and intravenous access is required in this situation, as it will result in death without treatment. This rhythm, or absence of rhythm, cannot be defibrillated. Epinephrine can be given every 3-5 minutes to attempt to restart the heart.

Sinus Pause— Sinus pauses occur when the impulses fail to stimulate heart contraction. Pauses may last from seconds to minutes and appear similar to ventricular asystole. Frequent pauses may lead to symptoms such as dizziness. The underlying cause for the pauses should be addressed; however, if no cause is identified or the pauses continue to be frequent and symptomatic, a pacemaker would be indicated.

Medications

Some medications can be used to prevent or treat dysrhythmias. There are four classes of medications that can be used. These medications act on the conduction system of the heart and help to control ventricular and/or atrial impulses. Review these medications and classes as you prepare for your exam.

Class I: sodium channel blockers (quinidine, lidocaine, procainamide)
Class II: beta-receptor blockers (esmolol, propranolol)
Class III: amiodarone and ibutilide (slow repolarization)
Class IV: calcium channel blockers (diltiazem, verapamil)
Unclassified: adenosine