Ventricular standstill (asystole)

Ventricular standstill (Figures 9-27 and 9-28 and Box 9-7) is the absence of all electrical activity in the ventricles. When the ventricles are inactive, there are no QRS complexes. The atria, however, may continue to generate electrical activity, producing P waves. Thus, ventricular standstill has two presentations on the ECG tracing: P waves without QRS complexes (Figure 9-27) or a straight line (Figure 9-28).

If P waves are present, some form of advanced heart block (Mobitz II second-degree AV block or third-degree AV block) may have preceded the arrhythmia. Ventricular standstill with a straight line usually occurs following such arrhythmias as VT, VF, IVR, and pulseless electrical activity. Asystole may also occur following termination of a tachyarrhythmia by medications, defibrillation, or cardioversion. Occasionally, ventricular standstill may occur without an obvious precipitating cause. In Figure 9-27, asystole occurred during the pause following a PAC.

Conditions contributing to the development of ventricular standstill include extensive myocardial damage (from ischemia or infarction), hypoxia, hyperkalemia, hypokalemia, hypothermia, drug overdose, and advanced heart block. Cardiac trauma may also be a contributing factor.

Once ventricular standstill occurs, there is no cardiac output, peripheral pulses and blood pressure are absent, and the patient becomes unconscious immediately. Cyanosis and seizure activity may also be present. Death is imminent unless the arrhythmia is treated immediately. Without cardiac monitoring, ventricular standstill cannot be distinguished from VF at the bedside.

Treatment protocols: Ventricular standstill (asystole)

¦  Check pulse and rapidly assess the patient. If there is a pulse and the patient is conscious, ventricular standstill is not the problem.

¦  Check monitor lead system (a loose electrode pad or lead wire will show a straight line).

¦  Check rhythm in two leads (low amplitude QRS complexes may look like P waves; fine VF may look like a straight line).

¦  Start CPR, establish an IV line, and ventilate the patient. Intubate the patient when possible.

¦  Give epinephrine 1 mg IV push and repeat every 3 to 5 minutes. Vasopressin 40 units IV push may be given

Box 9-7.

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