What rhythm?
Ventricular Fibrillation- characterized by erratic, rapid, and completely ineffective depolarization of the ventricles. Rather than contracting, the ventricles quiver. This rhythm is fatal if not corrected quickly. Precipitating causes of ventricular fibrillation include:
Myocardial ischemia or infarction.
Shock.
Electrocution.
Stimulant overdose.
Ventricular tachycardia (including torsades de pointes).
What rhythm?
Pulseless Ventricular Tachycardia- Patients in ventricular tachycardia may or may not have a pulse. Pulseless ventricular tachycardia occurs when the ventricles are not contracting effectively enough to sustain sufficient cardiac output. Underlying causes of pulseless ventricular tachycardia include:
Heart disease or damage (as from myocardial infarction).
Certain medications.
Electrolyte imbalances.
What rhythm?
Torsades de pointes- highly unstable form of ventricular tachycardia that may revert to sinus rhythm or degenerate into pulseless ventricular tachycardia or ventricular fibrillation. Torsades de pointes most often accompanies prolonged QT intervals, which may be the result of:
A congenital condition.
Acute myocardial infarction.
Medications (including amiodarone or other antiarrhythmics, certain antibiotics and certain antidepressants).
Drug–drug interactions.
The risk for torsades de pointes is increased when the corrected QT interval (QTc) is greater than 500 milliseconds.
What rhythm?
Pulseless electrical activity (PEA)- term used to describe several rhythms that are organized on ECG (i.e., the QRS complexes are similar in appearance) but the patient has no appreciable pulse. The heart’s conduction system is functioning, but the myocardium is not contracting (or contracting too weakly) to produce cardiac output, or the volume is not sufficient to maintain cardiac output.
PEA may be seen immediately after successful defibrillation of a patient with ventricular fibrillation or pulseless ventricular tachycardia. But when PEA is the presenting rhythm (“primary PEA”), the underlying cause is usually a condition that either affects contractility or ejection (e.g., hypoxia, acidosis, anterior myocardial infarction) or leads to inadequate preload (e.g., severe hypovolemia, pulmonary embolism, tension pneumothorax, cardiac tamponade, right ventricular infarction).
What rhythm?
Asystole- there is no electrical activity and therefore no contraction. Asystole is often the terminal rhythm in untreated pulseless ventricular tachycardia or ventricular fibrillation, or when resuscitation efforts are unsuccessful. Other causes include:
Indirect lightning strike.
Drowning.
Narcotic drug overdose.
Hypothermia.
Pulmonary embolism.
Hyperkalemia.
Stroke.
Describe the rhythm and QRS complex in Ventricular Fibrillation.
Irregular rhythm and chaotic, nondiscernible QRS.
Ventricular Fibrillation- rhythm is irregular, and there are no discernible P waves, QRS complexes, or T waves. The waveforms that are seen may vary in amplitude, from coarse to fine. As ventricular fibrillation progresses, the waveforms may change from coarse to fine and eventually disappear (asystole).
Regularity: irregular
Rate: not measurable
P wave: not discernible
QRS complex: chaotic, not discernible
PR interval: not discernible
Describe the ventricular rate and QRS complexes in Pulseless Ventricular Tachycardia.
The ventricular rate is usually greater than 180 bpm, and the QRS complexes are very wide.
Pulseless Ventricular Tachycardia:
Regularity: regular or irregular
Rate: > 100 bpm
P wave: not discernible
QRS complex: ≥ 0.12 second
PR interval: not discernible
What are the clues to whether the PEA is of cardiac or noncardiac origin?
Cardiac origin- slow rate and wide QRS
Noncardiac origin- rapid rate and narrow QRS
Pulseless Electrical Activity
The QRS complexes are similar in appearance and may be narrow or wide. The rate may be fast or slow. The 12-lead ECG allows for accurate determination of the duration of the QRS complexes and is useful for narrowing the list of possible underlying causes for PEA.
In PEA, the monitor shows an identifiable rhythm, but no pulse can be palpated. The rhythm may be sinus, atrial, junctional, or ventricular in origin. The QRS complexes are similar in appearance.
How is Asystole characterized? It is important to differentiate Asystole from?
Asystole is characterized by a lack of discernible electrical activity on ECG. It is important to differentiate Asystole from fine Ventricular Fibrillation.
Although asystole is said to have a “flatline” appearance, there is some fluctuation from the baseline. It is important to differentiate asystole from fine ventricular fibrillation; to do this, look at another lead or rotate the defibrillator paddles 90 degrees to evaluate the electrical activity in another plane.
Very rarely, the sinoatrial (SA) node may generate impulses that cause atrial depolarization but are completely blocked at the atrioventricular (AV) node, resulting in “P-wave asystole.”
Regularity: not discernible
Rate: not discernible
P wave: usually absent
QRS complex: not discernible
PR interval: not discernible
What do all cardiac arrest rhythms have in common?
All cardiac arrest rhythms are pulseless. The first step in recognizing a cardiac arrest rhythm is establishing that the patient does not have a pulse by checking for a carotid or femoral pulse.
Which ECG findings are seen in pulseless ventricular tachycardia?
In pulseless ventricular tachycardia, P waves are indiscernible and the QRS complexes are very wide (greater than 0.12 second in duration). The atrial rate in ventricular tachycardia is unmeasurable but the ventricular rate is usually greater than 180 bpm.
Waveforms of varying amplitude is a characteristic of ventricular fibrillation, NOT ventricular tachycardia.
A patient’s presenting rhythm is pulseless electrical activity (PEA). Which pathophysiologic mechanisms are most likely?
When PEA is the presenting rhythm, the underlying pathophysiologic mechanism is usually either impaired contractility or inadequate preload. The heart’s conduction system is functioning but either the myocardium is not contracting (or contracting too weakly) to produce cardiac output, or the volume is insufficient to maintain cardiac output.
Which conditions can precipitate ventricular fibrillation?
Causes of ventricular fibrillation include myocardial ischemia or infarction, shock, ventricular tachycardia, electrocution and stimulant overdose.
It is important to differentiate asystole from what other cardiac arrest rhythm?
Ventricular Fibrillation
