Chapter 22
After performing an ECG on an adult client, the nurse reports that the PR interval reflects normal sinus rhythm. What is the PR interval for a normal sinus rhythm?
0.12 and 0.2 seconds.
The nurse recognizes which as being true of cardioversion?
Defibrillator should be set to deliver a shock during the QRS complex
Which nursing intervention is required to prepare a client with cardiac dysrhythmia for an elective electrical cardioversion?
Instruct the client to restrict food and oral intake
Which ECG waveform characterizes conduction of an electrical impulse through the left ventricle?
QRS complex
The nurse is providing teaching to a client with an implanted cardiac device. Which client statement indicates that teaching has been effective?
"I will not place my cell phone in my chest pocket." The implantable cardioverter defibrillator (ICD) is an electronic device that detects and terminates life-threatening episodes of tachycardia or fibrillation, especially those that are ventricular in origin. An ICD has a generator about the size of a pack of chewing gum that is implanted in a subcutaneous pocket, usually in the upper chest wall. Because of this, electronic devices should not be placed near the implanted generator as this could cause electromagnetic interference. There is no reason for the client to stop using the microwave oven. Since the MRI is a large magnetic field, MRIs should not be done in the future. A client is not restriced from flying due to having a pacemaker..
A nurse is performing discharge teaching with a client who has an implantable cardioverter defibrillator (ICD) placed. Which client statement indicates effective teaching? q
"I'll keep a log of each time my ICD discharges."
Two nursing students are reading EKG strips. One of the students asks the instructor what the P-R interval represents. The correct response should be which of the following?
"It shows the time needed for the SA node impulse to depolarize the atria and travel through the AV node."
The client asks the nurse to explain what is meant by a ventricular bigeminy cardiac rhythm. What is the best response by the nurse?
"The rhythm has a normal beat, then a premature beat pattern."
A client with a second-degree atrioventricular heart block, Type II is admitted to the coronary care unit. How will the nurse explain the need to monitor the client's electrocardiogram (ECG) strip to the spouse?
"The small box will transmit the heart rhythm to the central monitor all the time."
The nurse is caring for a client who had a permanent pacemaker surgically placed and is now ready for discharge. What statement made by the client indicates the need for more education?
"We will be getting rid of our microwave oven so it will not affect my pacemaker." Permanent pacemaker generators have filters that protect them from electrical interference from most household devices, motors, and appliances, so the client can keep the microwave oven. Clients are taught to check pulses daily, avoid large magnets, and report any incisional redness or swelling.
A home care nurse is visiting a left-handed client who has an implantable cardioverter-defibrillator (ICD) implanted in the left chest. The client is planning to go rifle hunting. How should the nurse respond?
"You can't shoot a rifle left-handed because the rifle's recoil will traumatize the ICD site."
The nurse is working with a client with a new onset of atrial fibrillation during a three-month follow-up visit. The healthcare provider is planning a cardioversion, and the client asks the nurse why there is a wait for the treatment. What is the best response by the nurse?
"Your atrial chambers may contain blood clots now, so you must take an anticoagulant for a few weeks before the cardioversion." Because of the high risk of embolization of atrial thrombi, cardioversion of atrial fibrillation that has lasted longer than 48 hours should be avoided unless the client has received warfarin for at least 3 to 4 weeks prior to cardioversion. The doctor will not wait for a change in rhythm. Resting the heart will not change the rhythm. There is no delay but safer for the clots to be dissolved with the anticoagulant.
The nurse would expect which atrial rate to be an idioventricular rhythm?
20-40 The rate is 20 to 40. If the rate exceeds 40, the rhythm is known as accelerated idioventricular rhythm (AIVR). The rate is not measurable in asystole. Ventricular tachycardia has a rate of 100 to 250 per minute. Atrial flutter has a rate of 220 to 350.
A client is admitted to the emergency department reporting chest pain and shortness of breath. The nurse notes an irregular rhythm on the bedside electrocardiograph monitor. The nurse counts 9 RR intervals on the client's 6-second rhythm tracing. The nurse correctly identifies the client's heart rate as
90 bpm An alternative but less accurate method for estimating heart rate, which is usually used when the rhythm is irregular, is to count the number of RR intervals in 6 seconds and multiply that number by 10. The RR intervals are counted, rather than QRS complexes, because a computed heart rate based on the latter might be inaccurately high. The same methods may be used for determining atrial rate, using the PP interval instead of the RR interval. In this instance, 9 × 10 = 90.
The nurse is assigned the following client assignment on the clinical unit. For which client does the nurse anticipate cardioversion as a possible medical treatment?
A client with atrial arrhythmias
A nurse provides evening care for a client wearing a continuous telemetry monitor. While the nurse is giving the client a back rub, the client 's monitor alarm sounds and the nurse notes a flat line on the bedside monitor system. What is the nurse's first response?
Assess the client and monitor leads.
The nurse cares for a client with a dysrhythmia and understands that the P wave on an electrocardiogram (ECG) represents which phase of the cardiac cycle?
Atrial depolarization
The nurse knows that electrocardiogram (ECG) characteristics of atrial fibrillation include what?
Atrial rate of 300 to 400
A client has had a pacemaker implanted and the nurse will begin client education upon the client becoming alert. Which postimplantation instructions must be provided to the client with a permanent pacemaker?
Avoid sources of electrical interference. The nurse must instruct the client with a permanent pacemaker to avoid sources of electrical interference, such as MRI devices, large industrial motors, peripheral nerve stimulators, etc.
The nurse is providing discharge instructions to a client after a permanent pacemaker insertion. Which safety precaution will the nurse communicate to the client?
Avoid undergoing magnetic resonance imaging (MRI). A client with a pacemaker should avoid undergoing an MRI because the magnet could disrupt pacemaker function and cause injury to the client. Disruption is less likely to occur with newer microwave ovens. The client must avoid vigorous arm and shoulder movement only for the first 6 weeks after pacemaker implantation. Airport metal detectors don't harm pacemakers; however, the client should notify airport security guards that he has a pacemaker because its metal casing and programming magnet could trigger the metal detector.
A nurse provides morning care for a client in the intensive care unit (ICU). Suddenly, the bedside monitor shows ventricular fibrillation and the client becomes unresponsive. After calling for assistance, what action should the nurse take next?
Begin cardiopulmonary resuscitation
The nurse in the intensive care unit (ICU) hears an alarm sound in the patient's room. Arriving in the room, the patient is unresponsive, without a pulse, and a flat line on the monitor. What is the first action by the nurse?
Begin cardiopulmonary resuscitation (CPR)
A patient has had several episodes of recurrent tachydysrhythmias over the last 5 months and medication therapy has not been effective. What procedure should the nurse prepare the patient for?
Catheter ablation therapy Catheter ablation destroys specific cells that are the cause or central conduction route of a tachydysrhythmia. It is performed with or after an electrophysiology study. Usual indications for ablation are atrioventricular nodal reentry tachycardia, a recurrent atrial dysrhythmia (especially atrial fibrillation), or ventricular tachycardia unresponsive to previous therapy (or for which the therapy produced significant side effects).
After evaluating a client for hypertension, a health care provider orders atenolol, 50 mg P.O. daily. Which therapeutic effect should atenolol have in treating hypertension?
Decreased cardiac output and decreased systolic and diastolic blood pressure
The nurse is assessing a patient with a probable diagnosis of first-degree AV block. The nurse is aware that this dysrhythmia is evident on an ECG strip by what indication?
Delayed conduction, producing a prolonged PR interval First-degree AV block may occur without an underlying pathophysiology, or it can result from medications or conditions that increase parasympathetic tone. It occurs when atrial conduction is delayed through the AV node, resulting in a prolonged PR interval.
A nurse evaluates a client with a temporary pacemaker. The client's ECG tracing shows each P wave followed by the pacing spike. What is the nurse's best response?
Document the findings and continue to monitor the client
A client has been living with an internal, fixed-rate pacemaker. When checking the client's readings on a cardiac monitor the nurse notices an absence of spikes. What should the nurse do?
Double-check the monitoring equipment.
The nurse is preparing a client for upcoming electrophysiology (EP) studies and possible ablation for treatment of atrial tachycardia. What information will the nurse include in the teaching?
During the procedure, the dysrhythmia will be reproduced under controlled conditions.
A client with an atrial dysrhythmia has come to the clinic for a follow-up appointment and to talk with the health care provider about options to stop this dysrhythmia. What procedure could be used to treat this client?
Elective electrical cardioversion Elective electrical cardioversion is a nonemergency procedure done by a physician to stop rapid, but not necessarily life-threatening, atrial dysrhythmias. Chemical cardioversion is not a procedure; it is drug therapy. A Mace procedure is a distractor for this question. Defibrillation is not an elective procedure.
The nurse is speaking with a client admitted with a dysrhythmia. The client asks the nurse to explain the "F waves" on the electrocardiogram. What is the nurse's best response?
F waves are flutter waves representing atrial activity. F waves are not representative of ventricular activity, nor are they normal parts of the heart's conduction system. F waves can be caused by chronic pulmonary disease, valvular disease, thyrotoxicosis, and open heart surgery; they are not caused by medication.
The nurse identifies which of the following as a potential cause of premature ventricular complexes (PVCs)?
Hypokalemia PVCs can be caused by cardiac ischemia or infarction, increased workload on the heart (e.g., exercise, fever, hypervolemia, heart failure, tachycardia), digitalis toxicity, acidosis, or electrolyte imbalances, especially hypokalemia.
The staff educator is teaching a class in arrhythmias. What statement is correct for defibrillation?
It is used to eliminate ventricular arrhythmias. The only treatment for a life-threatening ventricular arrhythmia is immediate defibrillation, which has the exact same effect as cardioversion, except that defibrillation is used when there is no functional ventricular contraction. It is an emergency procedure performed during resuscitation. The client is not sedated but is unresponsive. Defibrillation uses more electrical energy (200 to 360 joules) than cardioversion.
Which nursing intervention must a nurse perform when administering prescribed vasopressors to a client with a cardiac dysrhythmia?
Monitor vital signs and cardiac rhythm
To evaluate a client's atrial depolarization, the nurse observes which part of the electrocardiogram waveform?
P wave The P wave depicts atrial depolarization, or spread of the electrical impulse from the sinoatrial node through the atria. The PR interval represents spread of the impulse through the interatrial and internodal fibers, atrioventricular node, bundle of His, and Purkinje fibers. The QRS complex represents ventricular depolarization. The T wave depicts the relative refractory period, representing ventricular repolarization.
A healthy adult client is seeing a health care provider for an annual physical examination. While the nurse is taking the client's vital signs, the client states, "Occasionally, my heart skips a beat." The nurse believes that the client is experiencing what condition?
Premature atrial complex
When the nurse observes an electrocardiogram (ECG) tracing on a cardiac monitor with a pattern in lead II and observes a bizarre, abnormal shape to the QRS complex, the nurse has likely observed which of the following ventricular dysrhythmias?
Premature ventricular contraction (PVC) A PVC is an impulse that starts in a ventricle before the next normal sinus impulse. Ventricular bigeminy is a rhythm in which every other complex is a PVC. Ventricular tachycardia is defined as three or more PVCs in a row, occurring at a rate exceeding 100 beats per minute. Ventricular fibrillation is a rapid but disorganized ventricular rhythm that causes ineffective quivering of the ventricles.
The nurse assesses a client with a heart rate of 120 beats per minute. What are the known causes of sinus tachycardia?
hypovolemia
A client asks the nurse what causes the heart to be an effective pump. The nurse informs the client that this is due to the:
inherent rhythmicity of cardiac muscle tissue.
The nurse analyzes the electrocardiogram (ECG) tracing of a client newly admitted to the cardiac step-down unit with a diagnosis of chest pain. Which finding indicates the need for follow-up?
QT interval that is 0. 46 seconds long The QT interval that is 0.46 seconds long needs to be investigated. The QT interval is usually 0.32 to 0.40 seconds in duration if the heart rate is 65 to 95 bpm. If the QT interval becomes prolonged, the client may be at risk for a lethal ventricular dysrhythmia, called torsades de pointes. The other findings are normal.
A 28-year-old client presents to the emergency department, stating severe restlessness and anxiety. Upon assessment, the client's heart rate is 118 bpm and regular, the client's pupils are dilated, and the client appears excitable. Which action should the nurse take next?
Question the client about alcohol and illicit drug use. The client is experiencing sinus tachycardia. Since the client's findings of tachycardia, dilated pupils, restlessness, anxiety, and excitability can indicate illicit drug use (cocaine), the nurse should question the client about alcohol and illicit drug use. This information will direct the client's plan of care. Causes of tachycardia include medications that stimulate the sympathetic response, stimulants, and illicit drugs. The treatment goals for sinus tachycardia is usually determined by the severity of symptoms and directed at identifying and abolishing its cause. The other interventions may be implemented, but determining the cause of the tachycardia is essential.
The nurse is placing electrodes for a 12-lead electrocardiogram (ECG). The nurse would be correct in placing an electrode on which area for V1?
Right side of sternum, fourth intercostal space view V1, the electrodes would be placed on the right side of the sternum, fourth intercostal space. V2 is the left side of the sternum, fourth intercostal space. V3 is midway between V2 and V4. V4 is at the mid-clavicular line, fifth intercostal space.
A nurse is caring for a client who has been admitted to have a cardioverter defibrillator implanted. The nurse knows that implanted cardioverter defibrillators are used in which clients?
The automatic implanted cardioverter defibrillator (AICD) is an internal electrical device used for selected clients with recurrent life-threatening tachydysrhythmias. Therefore, options A, B, and C are incorrect.
A client with heart failure asks the nurse how dobutamine affects the body's circulation. What is the nurse's best response?
The medication increases the force of the myocardial contraction.
A client has been diagnosed with atrial fibrillation and has been prescribed warfarin therapy. What should the nurse prioritize when providing health education to the client?
The need to have regular blood levels drawn One drawback of warfarin therapy is the need to have blood levels drawn on a regular basis. The medication does not need to be taken on an empty stomach, and the client does not have to sit upright. Adequate fluid intake is useful in a general way, but the need for fluids is not increased by taking warfarin.
The licensed practical nurse is co-assigned with a registered nurse in the care of a client admitted to the cardiac unit with chest pain. The licensed practical nurse is assessing the accuracy of the cardiac monitor, which notes a heart rate of 34 beats/minute. The client appears anxious and states not feeling well. The licensed practical nurse confirms the monitor reading. When consulting with the registered nurse, which of the following is anticipated?
The registered nurse administering atropine sulfate intravenously The licensed practical nurse and registered nurse both identify that client's bradycardia. Atropine sulfate, a cholinergic blocking agent, is given intravenously (IV) to increase a dangerously slow heart rate. Lanoxin is not administered when the pulse rate falls under 60 beats/minute. It is dangerous to wait until the pulse rate increases without nursing intervention or administering additional medications until the imminent concern is addressed.
A patient who had a myocardial infarction is experiencing severe chest pain and alerts the nurse. The nurse begins the assessment but suddenly the patient becomes unresponsive, no pulse, with the monitor showing a rapid, disorganized ventricular rhythm. What does the nurse interpret this rhythm to be?
Ventricular fibrillation The most common dysrhythmia in patients with cardiac arrest is ventricular fibrillation, which is a rapid, disorganized ventricular rhythm that causes ineffective quivering of the ventricles. No atrial activity is seen on the ECG. The most common cause of ventricular fibrillation is coronary artery disease and resulting acute myocardial infarction. Ventricular fibrillation is always characterized by the absence of an audible heartbeat, a palpable pulse, and respirations.
The nurse is proving discharge instructions for a client with a new arrhythmia. Which statement should the nurse include?
Your family and friends may want to take a CPR class. Having friends and family learn to perform CPR will help the client manage the arrhythmia. Monitoring pulse rate at home also helps the client manage the condition. Antiarrhythmic medication should be taken on time. Lightheadedness and dizziness should be reported to the provider.
A patient with hypertension has a newly diagnosed atrial fibrillation. What medication does the nurse anticipate administering to prevent the complication of atrial thrombi?
warfarin
The licensed practical nurse is setting up the room for a client arriving at the emergency department with ventricular arrhythmias. The nurse is most correct to place which of the following in the room for treatment?
a defibrillator The nurse is most correct to place a defibrillator close to the client room if not in the room. The nurse realizes that clients with ventricular dysrhythmias are at a high risk for fatal heart dysrhythmia and death. A suction machine is used to remove respiratory secretions. Cardioversion is used in a planned setting for atrial dysrhythmias. An ECG machine records tracings of the heart for diagnostic purposes. Most clients with history of cardiac disorders have an ECG completed.
A client has a medical diagnosis of an advanced first-degree atrioventricular block and is symptomatic. What initial treatment will the nurse be prepared to complete?
administer an IV bolus of atropine
The nurse is working on a telemetry unit, caring for a client who develops dizziness and a second-degree heart block, Mobitz Type 1. What will be the initial nursing intervention?
administer an iv bolus of atropine
The nurse is caring for a client who is displaying a third-degree AV block on the EKG monitor. What is the priority nursing intervention for the client?
alerting the healthcare provider of the third-degree heart block The client may experience low cardiac output with third-degree AV block. The healthcare provider needs to intervene to preserve the client's cardiac output. Monitoring the blood pressure and heart rate are important, but not a priority. The identification of a code status during a heart block is not appropriate. IV fluids are not helpful if the heart is not perfusing.
Which of the following medication classifications is more likely to be expected when the nurse is caring for a client with atrial fibrillation?
anticoagulant
A client presents to the emergency department via ambulance with a heart rate of 210 beats/minute and a sawtooth waveform pattern per cardiac monitor. The nurse is most correct to alert the medical team of the presence of a client with which disorder?
atrial flutter Atrial flutter is a disorder in which a single atrial impulse outside the SA node causes the atria to contract at an exceedingly rapid rate. The atrioventricular (AV) node conducts only some impulses to the ventricle, resulting in a ventricular rate slower than the atrial rate, thus forming a sawtooth pattern on the heart monitor. Asystole is the absence of cardiac function and can indicate death. Premature ventricular contraction indicates an early electric impulse and does not necessarily produce an exceedingly rapid heart rate. Ventricular fibrillation is the inefficient quivering of the ventricles and indicative of a dying heart.
Which dysrhythmia has an atrial rate between 250 and 400, with saw-toothed P waves?
atrial flutter Atrial flutter occurs in the atrium and creates impulses at a regular atrial rate between 250 and 400 times per minute. The P waves are saw-toothed in shape. Atrial fibrillation causes a rapid, disorganized, and uncoordinated twitching of atrial musculature. Ventricular fibrillation is a rapid, disorganized ventricular rhythm that causes ineffective quivering of the ventricles. Ventricular tachycardia is defined as three or more PVCs in a row, occurring at a rate exceeding 100 beats per minute.
A nurse is caring for a client who's experiencing sinus bradycardia with a pulse rate of 40 beats/minute. The client's blood pressure is 80/50 mm Hg and the client reports dizziness. Which medication does the nurse anticipate administering to treat bradycardia?
atropine
The nurse is caring for a client with second-degree atrioventricular block, Type I with symptomatic bradycardia. What is the most likely medication the nurse will administer?
atropine sulfate Atropine blocks acetylcholine at parasympathetic neuroeffector sites and blocks vagal stimulation. The client will be treated with an anticholinergic that blocks the effects of the vagal nerve. Atenolol and nadolol are beta blockers that are used for chest pain, myocardial infarction, and hypertension. Diltiazem is a calcium channel blocker used to treat angina or slow the heart rate.
When the appropriate electrocardiogram (ECG) complex follows the pacing spike, it is said to be
captured Capture is a term used to denote that the appropriate electrocardiogram (ECG) complex followed by the pacing spike. Triggered response means that the pacemaker will respond when it senses intrinsic heart activity. Inhibited response means that the response of the pacemaker is controlled by the activity of the client's heart.
The nurse witnesses a client experiencing ventricular fibrillation. What is the nurse's priority action?
defibrillation Advanced cardiac life support recommends early defibrillation for witnessed ventricular fibrillation. A cardioversion is used with a client who has a pulse. Atropine is used for bradycardia and dobutamine is an inotropic medication used to increased cardiac output.
A client reports light-headedness, chest pain, and shortness of breath. They physician orders tests to ascertain what is causing the client's problems. Which test is used to identify cardiac rhythms?
electrocardiogram
A client experiences a faster-than-normal heart rate when drinking more than two cups of coffee in the morning. What does the nurse identify on the electrocardiogram as an indicator of sinus tachycardia?
heart rate of 118 bpm The sinus node creates an impulse at a faster-than-normal rate. The PR interval of 0.1 seconds, QRS duration of 0.16 seconds and Q wave of 0.04 seconds are consistent with a normal sinus rhythm. Sinus tachycardia occurs when the heart rate is over 100 bpm.
A patient has a persistent third-degree heart block and has had several periods of syncope. What priority treatment should the nurse anticipate for this patient?
insertion of a pace maker
A client with dilated cardiomyopathy is having frequent episodes of ventricular fibrillation. What medical treatment does the nurse anticipate the client will have to terminate the episode of ventricular fibrillation?
internal cardioverter defibrillator insertion
A patient is 2 days postoperative after having a permanent pacemaker inserted. The nurse observes that the patient is having continuous hiccups as the patient states, "I thought this was normal." What does the nurse understand is occurring with this patient?
lead wire dislodgement Phrenic nerve, diaphragmatic (hiccupping may be a sign), or skeletal muscle stimulation may occur if the lead is dislocated or if the delivered energy (mA) is set high. The occurrence of this complication is avoided by testing during device implantation.
The nurse analyzes a 6-second electrocardiogram (ECG) tracing. The P waves and QRS complexes are regular. The PR interval is 0.18 seconds long, and the QRS complexes are 0.08 seconds long. The heart rate is calculated at 70 bpm. The nurse correctly identifies this rhythm as
normal sinus rhythm The electrocardiogram (ECG) tracing shows normal sinus rhythm (NSR). NSR has the following characteristics: ventricular and atrial rate: 60 to 100 beats per minute (bpm) in the adult; ventricular and atrial rhythm: regular; and QRS shape and duration: usually normal, but may be regularly abnormal; P wave: normal and consistent shape, always in front of the QRS; PR interval: consistent interval between 0.12 and 0.20 seconds and P:QRS ratio: 1:1.
The nurse is assessing vital signs in a patient with a permanent pacemaker. What should the nurse document about the pacemaker?
pacer rate
A client is diagnosed with a dysrhythmia at a rate slower than 60 beats/minute with a regular interval between 0.12 and 0.20 seconds. What type of dysrhythmia does the client have?
sinus brady
When the nurse observes that the client's heart rate increases during inspiration and decreases during expiration, the nurse reports that the client is demonstrating
sinus dysrhythmia. Sinus dysrhythmia occurs when the sinus node creates an impulse at an irregular rhythm. Normal sinus rhythm occurs when the electrical impulse starts at a regular rate and rhythm in the SA node and travels through the normal conduction pathway. Sinus bradycardia occurs when the sinus node regularly creates an impulse at a slower-than-normal rate. Sinus tachycardia occurs when the sinus node regularly creates an impulse at a faster-than-normal rate.
A client's Holter monitor strip reveals a heart rate with normal conduction but with a rate consistently above 105 beats/minute. What type of dysrhythmia would the cardiologist likely diagnose?
sinus tachycardia Sinus tachycardia is a dysrhythmia that proceeds normally through the conduction pathway but at a faster than usual rate (100 to 150 beats/minute).
A patient comes to the emergency department with reports of chest pain after using cocaine. The nurse assesses the patient and obtains vital signs with results as follows: blood pressure 140/92, heart rate 128, respiratory rate 26, and an oxygen saturation of 98%. What rhythm on the monitor does the nurse anticipate viewing?
sinus tachycardia Sinus tachycardia occurs when the sinus node creates an impulse at a faster-than-normal rate. Causes include medications that stimulate the sympathetic response (e.g., catecholamines, aminophylline, atropine), stimulants (e.g., caffeine, nicotine), and illicit drugs (e.g., amphetamines, cocaine, Ecstasy).
The nurse documents that a client is having a normal sinus rhythm. What characteristics of this rhythm has the nurse assessed?
the SA node initiates the impulse
The nurse working in the emergency department places a client in anaphylactic shock on a cardiac monitor and sees the cardiac rhythm shown. Which dysrythmia should the nurse document?
ventricular tachycardia The dysrhythmia shown is ventricular tachycardia because it has more than 3 premature ventricular contractions. The ventricular rate is 100 to 200 bpm; the atrial rate depends on the underlying rhythm (e.g., sinus rhythm). The QRS duration is 0.12 seconds or more and has an abnormal shape. . Ventricular asystole is characterized by absent QRS complexes; this rhythm is referred to as flatline. Normal sinus rhythm is regular with with a ventricular and atrial rate of 60 to 100 bpm. The P-wave has a consistent shape and is always in front of the QRS. The PR interval is a consistent interval between 0.12 and 0.20 seconds, and the P:QRS ratio is 1:1. A junctional rhythm not caused by a complete heart block has a ventricular rate of 40 to 60 bpm and, if P waves are discernible, an atrial rate of 40 to 60 bpm. The ventricular and atrial rhythm are regular. If the P-wave is in front of the QRS, the PR interval is less than 0.12 seconds. The P:QRS ratio is 1:1 or 0:1. Atrial fibrillation is indicated by an atrial rate of 300 to 600 bpm; the ventricular rate is usually 120 to 200 bpm if untreated. Both the ventricular and atrial rhythm are highly irregular. P-waves will not be discernible; irregular undulating waves that vary in amplitude and shape are referred to as fibrillatory or f waves. The PR interval cannot be measured, and the P:QRS ratio is Many:1.
