7
Ventricular arrhythmias
Just the facts
In this chapter, you’ll learn:
the proper way to identify various ventricular arrhythmias
the role of the ventricles in arrhythmia formation
the causes, significance, treatment, and nursing implications of each arrhythmia
assessment findings associated with each arrhythmia
interpretation of ventricular arrhythmias on an ECG.
A look at ventricular arrhythmias
Ventricular arrhythmias originate in the ventricles below the bundle of His. They occur when electrical impulses depolarize the myocardium using a different pathway from normal impulses.
Ventricular arrhythmias appear on an ECG in characteristic ways. The QRS complex is wider than normal because of the prolonged conduction time through the
ventricles. The T wave and the QRS complex deflect in opposite directions because of the difference in the action potential during ventricular depolarization and repolarization. Also, the P wave is absent because atrial depolarization doesn’t occur.
No kick from the atria
When electrical impulses are generated from the ventricles instead of the atria, atrial kick is lost and cardiac output decreases by as much as 30%. Patients with ventricular arrhythmias may show signs and symptoms of cardiac decompensation, including hypotension, angina, syncope, and respiratory distress.
Ventricular arrhythmias appear on an ECG in characteristic ways.
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Potential to kill
Although ventricular arrhythmias may be benign, they’re potentially deadly because the ventricles are ultimately responsible for cardiac output. Rapid recognition and treatment of ventricular arrhythmias increases the chance for successful resuscitation.
Premature ventricular contraction
A premature ventricular contraction (PVC) is an ectopic beat that may occur in healthy people without causing problems. PVCs may occur singly, in clusters of two
or more, or in repeating patterns, such as bigeminy or trigeminy. (See Identifying PVCs.) When PVCs occur in patients with underlying heart disease, they may indicate impending lethal ventricular arrhythmias.
Memory jogger
To help you remember the characteristics
of PVCs, think of 1, 2, 3. PVCs may occur singly (1), in clusters of two or more (2), or in repeating patterns,
such as bigeminy (2) (bimeans 2 or every other beat) and trigeminy (3) (trimeans 3 or every third beat).
How it happens
PVCs are usually caused by electrical irritability in the ventricular conduction system or muscle tissue. This irritability may be provoked by anything that disrupts normal electrolyte shifts during cell depolarization and repolarization. Conditions that can disrupt electrolyte shifts include:
•electrolyte imbalances, such as hypokalemia, hyperkalemia, hypomagnesemia, and hypocalcemia
•metabolic acidosis
•hypoxia
•myocardial ischemia and infarction
•drug intoxication, particularly cocaine, amphetamines, and tricyclic antidepressants
•enlargement of the ventricular chambers
•increased sympathetic stimulation
•myocarditis
•caffeine or alcohol ingestion
•proarrhythmic effects of some antiarrhythmics
•tobacco use.
This could get serious
PVCs are significant for two reasons. First, they can lead to more serious arrhythmias, such as ventricular tachycardia or ventricular fibrillation. The risk of developing a more serious arrhythmia increases in patients with ischemic or damaged hearts.
PVCs also decrease cardiac output, especially if the ectopic beats are frequent or sustained. Decreased cardiac output is caused by reduced ventricular diastolic filling time and a loss of
People with damaged hearts are more likely to develop serious arrhythmias.
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Don’t skip this strip
Identifying PVCs
This rhythm strip illustrates premature ventricular contraction (PVC) on beats 1, 6, and 11. Look for these distinguishing characteristics.
Premature QRS
complex appears wide and bizarre.
1 |
6 |
11 |
•Rhythm: Irregular
•Rate: 120 beats/minute
•P wave: Absent with PVC, but present with other QRS complexes
The rhythm is irregular.
•PR interval: 0.12 second in underlying rhythm
•QRS complex: Early with bizarre configuration and duration of
0.14 second in PVC; 0.08 second in underlying rhythm
•T wave: Normal; opposite direction from QRS complex with PVC
•QT interval: 0.28 second with underlying rhythm
•Other: Compensatory pause after PVC
atrial kick. The clinical impact of PVCs hinges on how well perfusion is maintained and how long the abnormal rhythm lasts.
What to look for
On the ECG strip, PVCs look wide and bizarre and appear as early beats causing atrial and ventricular irregularity. The rate follows the underlying rhythm, which is usually regular.
The P wave is usually absent. Retrograde P waves may be stimulated by the PVC and cause distortion of the ST segment. The PR interval and QT interval aren’t measurable on a premature beat, only on the normal beats.
Complex configuration
The QRS complex occurs early. Configuration of the QRS complex is usually normal in the underlying rhythm. The duration of the
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QRS complex in the premature beat exceeds 0.12 second. The T wave in the premature beat has a deflection opposite that of the QRS complex.
When a PVC strikes on the downslope of the preceding normal T wave—the R-on-T phenomenon—it can trigger more serious rhythm disturbances.
The pause that compensates
A horizontal baseline called a compensatory pause may follow the T wave of the PVC. When a compensatory pause appears, the interval between two normal sinus beats containing a PVC equals two normal sinus intervals. (See Compensatory pause.) This pause occurs because the ventricle is refractory and can’t respond to the next regularly timed P wave from the sinus node. When a compensatory pause doesn’t occur, the PVC is referred to as interpolated.
PVCs all in a row
PVCs that look alike are called uniform and may originate from the same ectopic focus. These beats may also appear in patterns that can progress to more lethal arrhythmias. (See When PVCs spell danger.)
Ruling out trouble
To help determine the seriousness of PVCs, ask yourself these questions:
•How often do they occur? In patients with chronic PVCs, an increase in frequency or a change in the pattern of PVCs from the baseline rhythm may signal a more serious condition.
•What pattern do they occur in? If the ECG shows a dangerous pattern—such as paired PVCs, PVCs with more than one shape, bigeminy, or R-on-T phenomenon—the patient may require immediate treatment.
•Are they really PVCs? Make sure the complex you see is a PVC, not another, less dangerous arrhythmia. (See Deciphering PVCs.) Don’t delay treatment, however, if the patient is unstable.
Outward signs tell a story
The patient with PVCs will have a much weaker pulse wave after the premature beat and a longer-than-normal pause between pulse waves. At times, you won’t be able to palpate any pulse after the PVC. If the carotid pulse is visible, however, you may see a weaker pulse wave after the premature beat. When auscultating for heart sounds, you’ll hear an abnormally early heart sound and a diminished amplitude with each premature beat.
Patients with frequent PVCs may complain of palpitations and may also experience hypotension or syncope.
Compensatory pause
You can determine if a compensatory pause exists by using calipers to mark off two normal P-P intervals. Place one leg of the calipers on the sinus P wave that comes just before the premature ventricular contraction. If the pause is compensatory, the other leg of the calipers will fall precisely on the P wave that comes after the pause.
Ask yourself specific questions to determine the seriousness of PVCs.
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When PVCs spell danger
Here are some examples of patterns of dangerous premature ventricular contractions (PVCs).
Paired PVCs
Two PVCs in a row are called a pair, or couplet (see highlighted areas). A pair can produce ventricular tachycardia because the second depolarization usually meets refractory tissue. A salvo—three or more PVCs in a row—is considered a run of ventricular tachycardia.
Multiform PVCs
PVCs that look different from one another arise from different sites or from the same site with abnormal conduction (see highlighted areas). Multiform PVCs may indicate increased ventricular irritability.
Bigeminy and trigeminy
PVCs that occur every other beat (bigeminy) or every third beat (trigeminy) may indicate increased ventricular irritability (see highlighted areas).
Mixed signals
Deciphering
PVCs
To determine whether the rhythm you’re assessing is a premature ventricular contraction (PVC) or some other beat, ask yourself these questions:
•Are you seeing ventricular escape beats rather than PVCs?
Escape beats act as a safety mechanism to protect the heart from ventricular standstill. The ventricular escape beat will be late, rather than premature.
•Are you seeing normal beats with aberrant ventricular conduction? Some supraventricular impulses may take an abnormal pathway through the ventricular conduction system, causing the QRS complex to appear abnormal. This aberrantly conducted beat will have a P wave, whereas a PVC doesn’t.
(continued)
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When PVCs spell danger (continued)
R-on-T phenomenon
In R-on-T phenomenon, the PVC occurs so early that it falls on the T wave of the preceding beat (see highlighted area). Because the cells haven’t fully repolarized, ventricular tachycardia or ventricular fibrillation can result.
How you intervene
If the patient is asymptomatic, the arrhythmia probably won’t require treatment. If he has symptoms or a dangerous form of PVCs, the type of treatment depends on the cause of the problem.
The practitioner may order procainamide (Procan), amiodarone (Cordarone), or lidocaine I.V. Potassium chloride may be given I.V. to correct hypokalemia, and magnesium sulfate I.V. may be given to correct hypomagnesemia. Other treatments may be aimed at adjusting drug therapy or correcting acidosis, hypothermia, or hypoxia.
Stat assessment
Patients who have recently developed PVCs need prompt assessment, especially if they have underlying heart disease or complex medical problems. Those with chronic PVCs should be observed closely for the development of more frequent PVCs or more dangerous PVC patterns.
Until effective treatment is begun, a patient with PVCs accompanied by serious symptoms should have continuous ECG monitoring and ambulate only with assistance. If the patient is discharged from the health care facility on antiarrhythmic drugs, family members should know how to contact the emergency medical service (EMS) and how to perform cardiopulmonary resuscitation (CPR).