VENTRICULAR FIBRILLATION |
141 |
|
Always assume the worst
Any wide QRS complex tachycardia should be treated as ventricular tachycardia until definitive evidence is found to establish another diagnosis, such as supraventricular tachycardia with abnormal ventricular conduction. Always assume that the patient has ventricular tachycardia and treat him accordingly. Rapid intervention will prevent cardiac decompensation or the onset of more lethal arrhythmias.
Teacher, teacher
Be sure to teach the patient and his family about the serious nature of this arrhythmia and the need for prompt treatment. If your patient is undergoing cardioversion, tell him he’ll be given an analgesic or a sedative to help prevent discomfort.
If a patient will be discharged with an ICD or a prescription for long-term antiarrhythmic drugs, teach his family how to contact the EMS and how to perform CPR.
Ventricular fibrillation
Ventricular fibrillation, commonly called V-fib, is a chaotic pattern of electrical activity in the ventricles in which electrical impulses arise from many different foci. It produces no effective muscular contraction and no cardiac output. Untreated ventricular fibrillation causes most cases of sudden cardiac death in people outside of a hospital.
How it happens
Causes of ventricular fibrillation include:
•myocardial ischemia
•MI
•untreated ventricular tachycardia
•underlying heart disease
•acid-base imbalance
•electric shock
•severe hypothermia
•electrolyte imbalances, such as hypokalemia, hyperkalemia, and hypercalcemia
•drug toxicity, including digoxin
•severe hypoxia.
VENTRICULAR ARRHYTHMIAS
142
Quivering ventricles
With ventricular fibrillation, the ventricles quiver instead of contract, so cardiac output falls to zero. If fibrillation continues, it leads to ventricular standstill and death.
What to look for
On the ECG strip, ventricular activity appears as fibrillatory waves with no recognizable pattern. Atrial rate and rhythm can’t be determined, nor can ventricular rhythm because no pattern or regularity occurs.
As a result, the ventricular rate, P wave, PR interval, QRS complex, T wave, and QT interval can’t be determined. Larger, or coarse, fibrillatory waves are easier to convert to a normal rhythm than are smaller waves because larger waves indicate a greater degree of electrical activity in the heart. (See Identifying ventricular fibrillation.)
No greater urgency
The patient in ventricular fibrillation is in full cardiac arrest, unresponsive, and without a detectable blood pressure or carotid or femoral pulse. Whenever you see a pattern resembling ventricular fibrillation, check the patient immediately, check the rhythm in another lead, and start treatment.
Be aware that other factors can mimic ventricular fibrillation on an ECG strip. Interference from an electric razor is one such mimic, as is muscle movement from shivering.
How you intervene
Defibrillation is the most effective treatment for ventricular fibrillation. (See “Pulseless arrest” in the appendix ACLS algorithms.) CPR must be performed until the defibrillator arrives to preserve oxygen supply to the brain and other vital organs. Assist with endotracheal intubation. Such drugs as epinephrine or vasopressin may help the heart respond better to defibrillation. Such drugs as amiodarone, lidocaine, procainamide, and magnesium sulfate may also be given.
A shock for life
During defibrillation, electrode paddles direct an electric current through the patient’s heart. The current causes the myocardium to depolarize, which, in turn, encourages the sinoatrial node to resume normal control of the heart’s electrical activity.
With V-fib,
the ventricles quiver instead of contract, so no pattern or regularity can be detected on the ECG strip.
VENTRICULAR FIBRILLATION |
143 |
|
Don’t skip this strip
Identifying ventricular fibrillation
The following rhythm strips illustrate coarse ventricular fibrillation (first strip) and fine ventricular fibrillation (second strip). Look for these distinguishing characteristics.
The presence of large fibrillatory waves indicates coarse ventricular fibrillation.
The presence of small fibrillatory waves indicates fine ventricular fibrillation.
• Rhythm: Chaotic |
• PR interval: Unmeasurable |
• QT interval: Not applicable |
• Rate: Undetermined |
• QRS complex: Indiscernible |
• Other: Waveform is a wavy line |
• P wave: Absent |
• T wave: Indiscernible |
|
One paddle is placed to the right of the upper sternum, and one is placed over the fifth or sixth intercostal space at the left anterior axillary line. During cardiac surgery, internal paddles are placed directly on the myocardium.
Automated-external defibrillators are increasingly being used to provide early defibrillation. In this method, electrode pads are placed on the patient’s chest and a microcomputer in the unit interprets the cardiac rhythm, providing the caregiver with step-by-step
VENTRICULAR ARRHYTHMIAS
144
instructions on how to proceed. These defibrillators can be used by people without medical experience.
Speed is the key
For the patient with ventricular fibrillation, successful resuscitation requires rapid recognition of the problem and prompt defibrillation. Many health care facilities and EMS providers have established protocols based on ACLS algorithms to help
health care workers initiate prompt treatment. Make sure you know where your facility keeps its emergency equipment and how to recognize and deal with lethal arrhythmias.
You’ll also need to teach your patient and his family how to contact the EMS. Fam-
ily members need instruction in CPR. Teach them about long-term therapies that prevent recurrent episodes of ventricular fibrillation, including chronic antiarrhythmic drugs and implantation of an ICD.
Asystole
Asystole is ventricular standstill. The patient is completely unresponsive, with no electrical activity in the heart and no cardiac output. This arrhythmia results most commonly from a prolonged period of cardiac arrest without effective resuscitation. It’s extremely important to distinguish asystole from fine ventricular fibrillation, which is managed differently. Therefore,
asystole must be confirmed in more than one ECG lead.
Asystole has been called the arrhythmia of death. The patient is in cardiopulmonary arrest. Without rapid initiation of CPR and appropriate treatment, the situation quickly becomes irreversible.
How it happens
Anything that causes inadequate blood flow to the heart may lead to asystole, including:
•MI
•severe electrolyte disturbances such as hyperkalemia
•massive pulmonary embolism
•prolonged hypoxemia
•severe, uncorrected acid-base disturbances
•electric shock
Patients and their families need to know when to contact EMS, how to perform CPR, and what long-term therapies are available, such as chronic antiarrhythmic drugs and ICDs.
ASYSTOLE 145
•drug intoxication such as cocaine overdose
•cardiac tamponade
•hypothermia.
What to look for
On the ECG strip, asystole looks like a nearly flat line (except for changes caused by chest compressions during CPR). No electrical activity is evident, except possibly P waves for a time. Atrial and ventricular activity is at a standstill, so no intervals can be measured. (See Identifying asystole.)
In the patient with a pacemaker, pacer spikes may be evident on the strip, but no P wave or QRS complex occurs in response to the stimulus.
The patient will be unresponsive, without any discernible pulse or blood pressure.
How you intervene
The immediate treatment for asystole is CPR. (See “Pulseless arrest” in the appendix ACLS algorithms.) Start CPR as soon as you determine that the patient has no pulse. Then verify the presence of asystole by checking two different ECG leads.
Don’t skip this strip
Identifying asystole
This rhythm strip illustrates asystole, the absence of electrical activity in the ventricles. Except for a few P waves or pacer spikes, nothing appears on the waveform and the line is almost flat.
The absence of electrical activity in the
ventricles results in a nearly flat line.
VENTRICULAR ARRHYTHMIAS
146
I can’t waste time
Pulseless electrical activity
In pulseless electrical activity, the heart muscle loses its ability to contract even though electrical activity is preserved. As a result, the patient goes into cardiac arrest.
On an electrocardiogram, you’ll see evidence of organized electrical activity, but you won’t be able to palpate a pulse or measure the blood pressure.
Causes
This condition requires rapid identification and treatment. Causes include hypovolemia, hypoxia, acidosis, tension pneumothorax, cardiac tamponade, massive pulmonary embolism, hypothermia, hyperkalemia, massive acute myocardial infarction, and an overdose of drugs such as tricyclic antidepressants.
Treatment
Cardiopulmonary resuscitation is the immediate treatment, along with epinephrine. Atropine may be given to patients with bradycardia. Subsequent treatment focuses on identifying and correcting the underlying cause.
Give repeated doses of epinephrine and atropine, as ordered. Transcutaneous pacing should be initiated as soon as possible. Subsequent treatment for asystole focuses on identifying and either treating or removing the underlying cause.
Quick recognition
Your job is to recognize this life-threatening arrhythmia and start resuscitation right away. Unfortunately, most patients with asystole can’t be resuscitated, especially after a prolonged period of cardiac arrest.
You should also be aware that pulseless electrical activity can lead to asystole. Know how to recognize this problem and treat it. (See Pulseless electrical activity.)
Arrhythmias can be lifethreatening. If asystole occurs, start CPR immediately.
ASYSTOLE 147
That’s a wrap!
Ventricular arrhythmias review
Overview of ventricular arrhythmias
•Originate in the ventricles, below the bundle of His
•Loss of atrial kick, decreasing cardiac output
•Potentially fatal without treatment or resuscitation
Characteristics
•QRS complex—wider than normal
•T wave and QRS complex deflect in opposite directions
•P wave is absent
Premature ventricular contraction
Characteristics
•Rhythms: Irregular during PVC; underlying rhythm may be regular
•Rates: Patterned after underlying rhythm
•P wave: Absent
•PR interval: Unmeasurable
•QRS complex: Wide and bizarre
•T wave: Opposite direction from QRS complex
•QT interval: Unmeasurable
•Other: Possible compensatory pause
Treatment
•Correction of the underlying cause
•Discontinuation of drug that may be causing toxicity
•Correction of electrolyte imbalances
•Procainamide, lidocaine, or amiodarone if warranted
Idioventricular rhythms
•Act as safety mechanism to prevent ventricular standstill
•Occur as escape beats, idioventricular rhythm, or accelerated idioventricular rhythm
Characteristics
• Rhythms: Atrial—undetermined; ventricular—usually regular
•Rates: Atrial—unmeasurable; ventricular—20 to 40 beats/minute
•P wave: Absent
•PR interval: Unmeasurable
•QRS complex: Wide and bizarre
•T wave: Deflection opposite that of QRS complex
•QT interval: Greater than 0.44 second
Treatment
•Atropine to increase heart rate
•Temporary or permanent pacemaker if arrhythmia is refractory to drugs
•Avoidance of drugs that suppress the idioventricular rhythm, such as lidocaine and other antiarrhythmics
Ventricular tachycardia
Characteristics
•Rhythms: Atrial—can’t be determined; ventricular— regular or slightly irregular
•Rates: Atrial—can’t be determined; ventricular—100 to 250 beats/minute
•P wave: Absent or hidden by QRS complex
•PR interval: Unmeasurable
•QRS complex: Wide and bizarre, with increased amplitude; duration greater than 0.12 second
•T wave: Opposite direction of QRS complex
•Other: Possible torsades de pointes
Treatment
ACLS protocols:
•Amiodarone; if patient is stable with monomorphic QRS complexes and drugs are unsuccessful, cardioversion
•Beta-adrenergic blockers, lidocaine, amiodarone, or procainamide, if patient’s ECG shows polymorphic QRS complexes and normal QT interval; cardioversion if unsuccessful
(continued)
VENTRICULAR ARRHYTHMIAS
148
Ventricular arrhythmias review (continued)
•Magnesium sulfate I.V. if patient shows polymorphic QRS and QT interval is prolonged, then overdrive pacing if rhythm persists (possibly also isoproterenol)
•Defibrillation; CPR, endotracheal intubation, and epinephrine or vasopressin, if patient is pulseless (possibly also consider amiodarone, lidocaine, or magnesium sulfate)
•Cardioverter-defibrillator possibly implanted for recurrent ventricular tachycardia
Torsades de pointes
•A form of polymorphic ventricular tachycardia
•Sometimes deteriorates into ventricular fibrillation
Characteristics
•Rhythms: Ventricular—irregular
•Rates: 150 to 250 beats/minute
•P wave: Usually absent
•PR interval: Unmeasurable
•QRS complex: Wide; rotates around the baseline; deflection downward and upward for several beats
Treatment
•Correction of the underlying cause
•Discontinuation of offending drug (usually one that lengthens the QT interval)
•Overdrive pacing
•Magnesium sulfate sometimes effective
•Cardioversion if unresponsive to other treatment
Ventricular fibrillation
•Electrical impulses arise from many different foci in the ventricles
•Produces no effective muscular contraction and no cardiac output
•If untreated, it causes most cases of sudden cardiac death out of hospital
Characteristics
•Rhythms: Can’t be determined
•Rates: Can’t be determined
•P wave: Can’t be determined
•PR interval: Can’t be determined
•QRS complex: Can’t be determined
•T wave: Can’t be determined
•QT interval: Isn’t applicable
•Other: Variations in size of fibrillatory waves
Treatment
ACLS protocols:
•Defibrillation
•Initiation of CPR
•Endotracheal intubation and administration of epinephrine or vasopressin (consider amiodarone, lidocaine, magnesium sulfate, or procainamide)
•Implantation of cardioverter-defibrillator if patient is at risk for recurrent ventricular fibrillation
Asystole
•Characterized by ventricular standstill and cardiac arrest
•Fatal without prompt CPR and treatment
Characteristics
• Lack of electrical activity seen on ECG as a nearly flat line
Treatment
ACLS protocols:
•Initiation of CPR
•Endotracheal intubation, transcutaneous pacing, and epinephrine and atropine
Pulseless electrical activity
Characteristics
•Electrical activity is present on ECG but heart muscle can’t contract
•Result is no palpable pulse or blood pressure and cardiac arrest
Treatment
ACLS protocols:
•Initiation of CPR
•Epinephrine
•Atropine for bradycardia
•Correction of the underlying cause
QUICK QUIZ |
149 |
|
Quick quiz
1.PVCs are most dangerous if they:
A.are multiformed and increase in frequency.
B.appear wide and bizarre.
C.occur after the T wave.
D.are uniform and wide.
Answer: A. PVCs that have different shapes (multiformed) and increase in frequency may signal increased ventricular irritability and progress to a lethal arrhythmia.
2. The treatment of choice for a patient with ventricular fibrillation is:
A.defibrillation.
B.transesophageal pacing.
C.synchronized cardioversion.
D.administration of epinephrine.
Answer: A. Patients with ventricular fibrillation are in cardiac arrest and require defibrillation.
3. Patients with a slow idioventricular rhythm that doesn’t respond to atropine should receive:
A.lidocaine.
B.dobutamine.
C.synchronized cardioversion.
D.transcutaneous pacing.
Answer: D. Transcutaneous pacing is a temporary way to increase the rate and ensure adequate cardiac output.
4.A compensatory pause occurs after a PVC because the:
A.atria conduct a retrograde impulse.
B.ventricle is refractory at that point.
C.bundle of His blocks sinus impulses to the ventricles.
D.atria are refactory and can’t respond.
Answer: B. A compensatory pause occurs because the ventricle is refractory and can’t respond to the next regularly timed P wave from the sinus node.
VENTRICULAR ARRHYTHMIAS
150
5. The term pulseless electrical activity refers to a condition in which there’s:
A.an extremely slow heart rate but no pulse.
B.asystole on a monitor or rhythm strip.
C.electrical activity in the heart but no actual contraction.
D.asystole and a palpable pulse and blood pressure.
Answer: C. Pulseless electrical activity is electrical activity without mechanical contraction. The patient is in cardiac arrest, with no blood pressure or pulse.
Test strips
Ready for a few test strips? Interpret the two strips below using the 8-step method. Fill in the blanks below with the particular characteristics of the strip and then check your answers with ours.
Strip 1
Atrial rhythm:
Ventricular rhythm:
Atrial rate:
Ventricular rate:
P wave:
PR interval:
QRS complex:
T wave:
QT interval:
Other:
Interpretation:
QUICK QUIZ |
151 |
|
Strip 2
Atrial rhythm:
Ventricular rhythm:
Atrial rate:
Ventricular rate:
P wave:
PR interval:
QRS complex:
T wave:
QT interval:
Other:
Interpretation:
Answers to test strips
1.Rhythm: Irregular ventricular rhythm Rate: Ventricular rate is 130 beats/minute P wave: Absent
PR interval: Unmeasurable
QRS complex: Wide and bizarre with varying duration T wave: Opposite QRS complex
QT interval: Unmeasurable Other: None
Interpretation: Ventricular tachycardia
2.Rhythm: Chaotic ventricular rhythm
Rate: Can’t be determined
P wave: Indiscernible
PR interval: Indiscernible
QRS complex: Indiscernible
T wave: Indiscernible
QT interval: Indiscernible
Other: None
Interpretation: Ventricular fibrillation
VENTRICULAR ARRHYTHMIAS
152
Scoring
If you answered all five questions correctly and filled in all the blanks as we did, sensational! You’re simply V-best.
If you answered four questions correctly and filled in most of the blanks pretty much as we did, super! You’ve got a great eye for those tricky ventricular rhythms.
If you answered fewer than four questions correctly and missed most of the blanks, that’s okay. Read this chapter again and you’ll get de pointes.
Keep going…you’re halfway through this book!