Tachycardia, Ventricular

SOURCE

Source: Sanoski CA, Bauman JL. The arrhythmias. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146057036. Accessed March 28, 2017.

DEFINITION

• Ventricular tachycardia (VT) is three or more consecutive premature ventricular complexes (PVCs) occurring at a rate greater than 100 beats/min.

ETIOLOGY

• Acute myocardial infarction (MI)

• Cardiomyopathy.

• Heart failure.

• Electrolyte abnormalities (hypokalemia, hypomagnesemia)

• Hypoxia.

• Drug toxicity (eg, digoxin)

PATHOPHYSIOLOGY

• Defined by ≥3 repetitive premature ventricular complexes (PVCs) occurring at rate of >100 beats/min.

• Nonsustained VT self-terminates after brief duration (usually <30 s).

• Sustained VT lasts >30 s.

• Monomorphic VT has consistent QRS configuration, whereas polymorphic VT has varying QRS complexes.

• Torsades de pointes (TdP) is polymorphic VT in which QRS complexes appear to undulate around central axis.

EPIDEMIOLOGY

• Incidence not known precisely because clinical findings overlap with ventricular fibrillation (VF).

• Approximately 300,000 deaths per year in the United States are caused by VT or VF.

• Incidence of sudden cardiac death is 53 per 100,000 population.

RISK FACTORS

• Prior MI

• Structural heart disease.

• Family history of premature sudden death.

CLINICAL PRESENTATION

SIGNS AND SYMPTOMS

• Symptoms:

  • Palpitations.

  • Dizziness.

  • Exercise intolerance.

  • Lightheadedness.

  • Syncope.

• Signs: Weak or absent pulse.

DIAGNOSIS

MEANS OF CONFIRMATION AND DIAGNOSIS

• Electrocardiogram (ECG) shows runs of ≥3 PVCs with rate >100 beats/min.

• TdP characterized by long QT intervals or prominent U waves on ECG.

LABORATORY TESTS

• Performed if underlying causes suspected, for example:

  • MI

  • Electrolyte imbalances.

  • Digoxin toxicity.

IMAGING

• ECG

DIAGNOSTIC PROCEDURES

• Electrophysiologic testing may help identify patients at increased risk for sudden death or candidates for radiofrequency ablation of tachycardia focus.

DIFFERENTIAL DIAGNOSIS

• Atrial tachycardia, flutter, or fibrillation

• Heart failure.

• Hypocalcemia, hypokalemia, hypomagnesemia

• MI

• Paroxysmal supraventricular tachycardia (PSVT)

• Ventricular fibrillation.

DESIRED OUTCOMES

• Identify and correct underlying causes.

• Resolve symptoms.

• Prevent recurrences.

• Avoid complications from treatment.

TREATMENT: NONPHARMACOLOGIC THERAPY

• If severe symptoms present, perform synchronized direct current cardioversion (DCC) immediately to restore sinus rhythm.

• Correct precipitating factors if possible.

• If VT isolated event with transient initiating factor (eg, acute MI, digitalis toxicity), long-term antiarrhythmic therapy not needed after correction of precipitating factors.

• Most patients with acute TdP require and respond to DCC, but TdP tends to be paroxysmal and often recurs rapidly after DCC.

• Automatic implantable cardioverter-defibrillator (ICD) highly effective for preventing sudden death due to recurrent VT or VF.