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Idioventricular rhythms
Called the rhythms of last resort, idioventricular rhythms act as safety mechanisms to prevent ventricular standstill when no impulses are conducted to the ventricles from above the bundle of His. The cells of the His-Purkinje system take over and act as the heart’s pacemaker to generate electrical impulses.
Idioventricular rhythms can occur as ventricular escape beats, idioventricular rhythm (a term used to designate a specific type of idioventricular rhythm), or accelerated idioventricular rhythm.
How it happens
Idioventricular rhythms occur when all of the heart’s other pacemakers fail to function or when supraventricular impulses can’t reach the ventricles because of a block in the conduction system. The arrhythmias may accompany third-degree heart block or be caused by:
•myocardial ischemia
•myocardial infarction (MI)
•digoxin toxicity
•beta-adrenergic blockers
•pacemaker failure
•metabolic imbalances.
Conduction foibles and pacemaker failures
Idioventricular rhythms signal a serious conduction defect with a failure of the primary pacemaker. The slow ventricular rate of these arrhythmias and the loss of atrial kick markedly reduce cardiac output. Patients require close observation because this problem can progress to more lethal arrhythmias. Idioventricular arrhythmias also commonly occur in dying patients.
What to look for
If just one idioventricular beat is generated, it’s called a ventricular escape beat. (See Identifying idioventricular rhythm, page 134.) The beat appears late in the conduction cycle, when the rate drops to 40 beats/minute.
Consecutive ventricular beats on the ECG strip make up idioventricular rhythm. When this arrhythmia occurs, atrial rhythm and rate can’t be determined. The ventricular rhythm is usually regular at 20 to 40 beats/minute, the inherent rate of the
Carefully monitor patients who have idioventricular rhythms.
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ventricles. If the rate is faster, it’s called an accelerated idioventricular rhythm. (See Accelerated idioventricular rhythm.)
A telltale arrhythmia
Distinguishing characteristics of idioventricular rhythm include an absent P wave or one that can’t conduct through to the ventricles. This makes the PR interval unmeasurable.
Because of abnormal ventricular depolarization, the QRS complex has a duration of longer than 0.12 second, with a wide and bizarre configuration. The T-wave deflection will be opposite the QRS complex. The QT interval is usually prolonged, indicating delayed depolarization and repolarization.
The patient may complain of palpitations, dizziness, or lightheadedness, or he may have a syncopal episode. If the arrhythmia persists, hypotension, weak peripheral pulses, decreased urine output, or confusion can occur.
Don’t skip this strip
Identifying idioventricular rhythm
This rhythm strip illustrates idioventricular rhythm. Look for these distinguishing characteristics.
The rate is below 40 beats/minute.
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The QRS complex is wide and bizarre. |
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• Rhythm: Regular |
• PR interval: Unmeasurable |
• QT interval: 0.60 second |
• Rate: Unable to determine atrial |
• QRS complex: Wide and bizarre |
• Other: None |
rate; ventricular rate of 35 beats/ |
• T wave: Deflection opposite QRS |
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minute |
complex |
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• P wave: Absent |
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Don’t skip this strip
Accelerated idioventricular rhythm
An accelerated idioventricular rhythm has the same characteristics as an idioventricular rhythm except that it’s faster. The rate shown here varies between 40 and 100 beats/minute.
The rate is between 40 and 100 beats/minute.
The QRS complex is wide and bizarre.
How you intervene
If the patient is symptomatic, treatment should be initiated immediately to increase his heart rate, improve cardiac output, and establish a normal rhythm. Atropine may be prescribed to increase the heart rate.
If atropine isn’t effective or if the patient develops hypotension or other signs of instability, a pacemaker may be needed to reestablish a heart rate that provides enough cardiac output to perfuse organs properly. A transcutaneous pacemaker may be used in an emergency until a temporary or permanent transvenous pacemaker can be inserted. (See Transcutaneous pacemaker, page 136.)
Remember: The goal of treatment doesn’t include suppressing the idioventricular rhythm because it acts as a safety mechanism to protect the heart from standstill. Idioventricular rhythm should never be treated with lidocaine or other antiarrhythmics that would suppress that safety mechanism.
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I can’t waste time
Transcutaneous pacemaker
In life-threatening situations in which time is critical, a transcutaneous pacemaker may be used to regulate heart rate. This device sends an electrical impulse from the pulse generator to the heart by way of two electrodes placed on the patient’s chest and back, as shown.
The electrodes are placed at heart level, on either side of the heart, so the electrical stimulus has only a short distance to travel to the heart. Transcutaneous pacing is quick and effective, but it may be painful. It’s used only until transvenous pacing can be started.
Anterior pacing
electrode Posterior pacing electrode
Continuous monitoring needed
Patients with idioventricular rhythms need continuous ECG monitoring and constant assessment until treatment restores hemodynamic stability. Keep pacemaker equipment at the bedside and have atropine readily available. Enforce bed rest until a permanent system is in place for maintaining an effective heart rate.
Be sure to tell the patient and his family about the serious nature of this arrhythmia and all aspects of treatment. If a permanent pacemaker is inserted, teach the patient and his family how
it works, how to recognize problems, when to contact the practitioner, and how pacemaker function will be monitored.
Teach the patient about how a pacemaker works and when to contact the
practitioner.