V: Ventricular Standstill (Asystole)

Ventricular Standstill (Asystole)

BASICS

DEFINITION

Absence of ventricular complexes on the ECG or absence of ventricular activity (electrical-mechanical dissociation).

ECG Features

Ventricular asystole can result from severe sinoatrial block or arrest or by third-degree AV block without a junctional or ventricular escape rhythm; ECG features include:
- P waves present if patient has complete AV block (Figure 1)
- P waves absent during asystole if patient has severe sinoatrial block or arrest
- No QRS complexes
- Electrical-mechanical dissociation—a recorded ECG cardiac rhythm (P-QRS-T) and no effective cardiac output or palpable femoral pulse.

Figure 1 Ventricular asystole in a dog with severe complete AV block. Only P wages (atrial activity) are present; there is no ventricular activity. (Lead II, 50 mm/second, 1 cm = 1 mV.) (From: Tilley LP. Essentials of Canine and Feline Electrocardiography, 3rd ed. Baltimore: Williams & Wilkins, 1992, with permission.)

PATHOPHYSIOLOGY

Ventricular asystole represents cardiac arrest; if the ventricular rhythm is not restored in 3–4 minutes, irreversible brain injury can occur.

SYSTEMS AFFECTED

Cardiovascular
All organ systems affected by loss of perfusion

GENETICS

N/A

INCIDENCE/PREVALENCE

Unknown

GEOGRAPHIC DISTRIBUTION

None

SIGNALMENT

Species

Dogs and cats

Breed Predilections

None

Mean Age and Range

Unknown

SIGNS

Historical Findings

Severe systemic illness or cardiac disease in many patients
Other cardiac arrhythmias in some
Syncope

Physical Examination Findings

No ventricular pulse can be palpated
Cardiac arrest
Collapse
Death

CAUSES

Complete AV block with absence of ventricular or junctional escape rhythm.
Severe sinus arrest or block.
Hyperkalemia (Figure 2).

RISK FACTORS

Any severe systemic illness (e.g., severe acidosis and hyperkalemia) or heart disease.
Hypoadrenocorticism causing hyperkalemia.
Urinary tract rupture or obstruction, resulting in hyperkalemia.

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

Rule-out ECG artifact; reapply ECG clips and make sure skin contact is good and adequate alcohol is applied to leads.

CBC/BIOCHEMISTRY/URINALYSIS

Severe hyperkalemia possible cause

OTHER LABORATORY TESTS

N/A

IMAGING

N/A

DIAGNOSTIC PROCEDURES

Systemic blood pressure—readable pressure absent

PATHOLOGIC FINDINGS

N/A

TREATMENT

APPROPRIATE HEALTH CARE

Asystole is a frequently fatal rhythm requiring immediate aggressive treatment.
Artificial pacing with a transvenous pacemaker may succeed if myocardium is mechanically responsive.
DC electrical conversion is not effective unless the rhythm can first be converted to ventricular fibrillation with medications.

NURSING CARE

Treat any treatable problems such as hypothermia, hyperkalemia, and acid-base disorders.

ACTIVITY

N/A

DIET

N/A

CLIENT EDUCATION

None

SURGICAL CONSIDERATIONS

None

MEDICATIONS

DRUG(S) OF CHOICE

Institute cardiopulmonary resuscitation.
Epinephrine 0.2 mg/kg IV, IT, or IL (double the dose for IT administration and deliver with equal volume of saline).
Atropine 0.05 mg/kg IV, IT, or IL (double the dose for IT administration and deliver with equal volume of saline).
Sodium bicarbonate 1 mEq/kg IV for each 10 minutes of cardiac arrest.
Dexamethasone and dopamine may be helpful in patients with electrical-mechanical dissociation.

CONTRAINDICATIONS

Drugs that depress sinus node or AV node conduction in patients with sinus arrest or heart block (e.g., beta-blockers, calcium channel blockers, digoxin).

PRECAUTIONS

None

Figure 2 Ventricular asystole in a cat with severe hyperkalemia (11 mEq/L) from urethral obstruction. No P waves or QRS complexes are seen after four wide and bizarre QRS complexes (atrial standstill with delayed ventricular conduction). (Lead II, 50 mm/sec, 1 cm = 1 mV.) (From: Tilley LP. Essentials of Canine and Feline Electrocardiography, 3rd ed. Baltimore: Williams & Wilkins, 1992, with permission.)

POSSIBLE INTERACTIONS

None

ALTERNATIVE DRUG(S)

Calcium gluconate—patients with ventricular standstill and hyperkalemia.

FOLLOW-UP

PATIENT MONITORING

If animal is resuscitated—evaluate CBC, biochemical analysis, and urinalysis.
If animal survives and primary cardiac disease is suspected—an echocardiogram and thoracic radiographs.
ECG—closely and frequently.

PREVENTION/AVOIDANCE

Careful monitoring of critically ill patients to prevent and correct acid-base disturbances, hypotension, and hypoxemia.

POSSIBLE COMPLICATIONS

Death
DIC and multiorgan failure

EXPECTED COURSE AND PROGNOSIS

Usually die. If sinus rhythm reestablished, prognosis still usually guarded to poor as not uncommon to arrest again.

MISCELLANEOUS

ASSOCIATED CONDITIONS

None

AGE-RELATED FACTORS

None

ZOONOTIC POTENTIAL

None

PREGNANCY/FERTILITY/BREEDING

None

SYNONYMS

Ventricular asystole