Cardiovascular Study Guide for the CCRN

Dysrhythmias

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

It’s important to note first what characterizes a normal heart rhythm, which is also called sinus rhythm: regular, narrow QRS complex (less than 0.12 seconds), PR interval less than 0.2 seconds, and a rate of 60 to 100 bpm.

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

There are numerous types of dysrhythmia that each have different symptoms, causes, and standards of treatment.

sinus bradycardia—Sinus bradycardia is classified by a decreased rate of heartbeat impulses. It has normal P waves and QRS complexes, but occurs at a rate of <50 to 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. For severe cases, transcutaneous (temporary) pacing or implantation (permanent) of a pacemaker may be needed.

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 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. Treat this by finding the underlying cause. Calcium channel blockers and beta-blockers help to reduce heart rate.

supraventricular tachycardia (SVT)—SVT is defined as a narrow QRS complex tachycardia, with a rate typically greater than 150 bpm with no P waves. At times, SVT ranges from 200 to 300 beats per minute. It has a quick onset, and the patient is more likely to be symptomatic than with sinus tachycardia. They may experience dizziness, chest pain, palpitations, and syncope. If not treated, it may decrease heart function and cause congestive heart failure. Causes are similar to sinus tachycardia, often either lifestyle related (stress, nicotine, alcohol, dehydration, etc.) or congenital (e.g., Wolff-Parkinson-White syndrome). Treatment for SVT includes adenosine, digoxin, verapamil, vagal maneuvers, and cardioversion. In some cases, cardiac ablation may be required.

Wolff-Parkinson-White syndrome—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, which is present at birth, may not become 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 in this condition, with only the rate and rhythm being mildly irregular. This is generally considered a normal variation. Treatment may be indicated if this rhythm occurs with bradycardia or if the patient is symptomatic.

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.

premature atrial contractions (PACs)—PACs 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. These are very common and usually require no treatment. If the PACs occur greater than six episodes per hour or with significant symptoms, further testing is indicated.

atrial fibrillation (a-fib)—A-fib is the most common arrhythmia. It is characterized by 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 reduced stroke volume and overactivity of the atrium. The atrial rate may be 300 to 600 beats per minute. The ventricular rate can be normal (<100 bpm), which would be referred to as controlled a-fib, or much higher (100 to 180 bpm or more), which would be referred to as uncontrolled or a-fib with rapid ventricular rate (RVR). The rate has a narrow QRS complex, irregularity, and no definitive P waves. It can be acute (e.g., developed after an illness/surgery) or chronic, with increased risk with aging, comorbidities, heart conditions, lifestyle factors, and genetic predispositions. Once you develop the arrhythmia, you are more likely to develop it again. The term paroxysmal refers to when the arrhythmia is intermittent. A-fib with RVR can make a patient unstable, so it is important to control the rate. Symptoms of this condition include chest pain, difficulty breathing, and decreased blood pressure. Because of the clotting risk, patients will need to be on anticoagulants. If unstable, cardioversion may be implemented. Medications to help slow the ventricular rate include non-dihydropyridine calcium channel blockers and beta-blockers. For converting back to sinus rhythm, Tikosyn® and amiodarone may be used.

atrial flutter—Atrial flutter is not as common as a-fib, but is similar in nature. It is characterized by a fast atrial rate, usually 250 to 400 beats per minute, with or without excessive ventricular activity (general rates are 75 to 150 beats per minute). It has a narrow QRS complex, a sawtooth pattern, no definitive P waves, and it can be regular or slightly irregular. Generally, atrial flutter does not cause as many symptoms since the rate does not rise as significantly. It still poses the same risk of blood clots, though. The causes and treatment are generally the same, and a person can have both a-fib and atrial flutter.

premature junctional contractions (PJCs)—Junctional dysrhythmias arise from the dysfunction of the area around the AV node. A PJC is a premature impulse to the AV node prior to the normal sinus impulse. It is similar to premature atrial contractions (PACs); however, PJCs may be a sign of digoxin toxicity. In this rhythm, the QRS complex may come early, and a P wave is inverted or absent. The interval of the rhythm is usually regular, and symptoms of this condition are rare.

junctional rhythms—Junctional rhythms occur when the AV node assumes the role of initiating the cardiac rhythm. Instead of sinus node impulse initiation, which occurs at 60 to 100 beats per minute, the atrial node dictates the pace at 40 to 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. The subset of rhythms is classified based on the rate: junctional bradycardia (less than 40 bpm), accelerated junctional (61 to 100 bpm), and junctional tachycardia (greater than 100 bpm).

premature ventricular contractions (PVCs)—PVCs occur when impulses begin in the ventricles during a beat cycle. The abnormal impulses cause an irregular QRS complex >0.12 seconds. Patients will also have an irregular heartbeat. PVCs can be caused by electrolyte imbalances, caffeine, nicotine, and alcohol. They frequently occur in a repetitive nature and can be classified based on when they occur: Bigeminy (PVC after every normal beat), Trigeminy (PVC after every 2 normal beats), Quadrigeminy (PVC after every 3 normal beats), Couplet (2 consecutive PVCs), and so forth. It may be a precursor to ventricular tachycardia, especially if there is a presence of more than six PVCs in one hour or frequent “runs” of PVCs where multiple PVCs occur consecutively (also referred to as non-sustained v-tach NSVT). 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 to 200 beats per minute. This rate of contraction disables the heart from pumping blood effectively. If sustained, it is classified into three categories: stable VT, unstable VT, and pulseless VT. The difference between stable and unstable is the patient’s status and whether they are symptomatic. 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, CPR is initiated, and the priority is to quickly perform emergency defibrillation. Epinephrine and amiodarone will be used to try to regain a normal rhythm.

Torsades de pointes—Also referred to as polymorphic ventricular tachycardia, a torsades de pointes is a type of v-tach that is life threatening and often preceded by a long QT interval. This is most commonly caused by medications that prolong the QT interval (e.g., ondansetron or haloperidol), hypokalemia, and hypomagnesia. Treatment includes ACLS protocol to initially stabilize the patient if pulseless, stopping medications that contribute to prolonged QT interval, and IV magnesium to stabilize the heart cell membrane and increase serum levels if low.

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. Having a long QT interval significantly increases your risk of developing torsades de pointes, a life-threatening arrhythmia.

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. Again, emergency defibrillation is the priority, followed by IV push epinephrine 1 mg every 3 to 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. It can be caused by electrolyte abnormalities, medications, and heart disease. The rate will be regular between 20 and 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 or have no palpable pulse. It is referred to as an accelerated idioventricular rhythm when the rate is above 40 bpm, and this variation can be benign and self-limiting.

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 to 5 minutes to attempt to restart the heart.

Medication

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, atropine