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SOURCE

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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.

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DEFINITION

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

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ETIOLOGY

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  • Acute myocardial infarction (MI)

  • Cardiomyopathy.

  • Heart failure.

  • Electrolyte abnormalities (hypokalemia, hypomagnesemia)

  • Hypoxia.

  • Drug toxicity (eg, digoxin)

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PATHOPHYSIOLOGY

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  • 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.

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EPIDEMIOLOGY

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  • 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.

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RISK FACTORS

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  • Prior MI

  • Structural heart disease.

  • Family history of premature sudden death.

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CLINICAL PRESENTATION

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SIGNS AND SYMPTOMS
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  • Symptoms:

    • Palpitations.

    • Dizziness.

    • Exercise intolerance.

    • Lightheadedness.

    • Syncope.

  • Signs: Weak or absent pulse.

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DIAGNOSIS

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MEANS OF CONFIRMATION AND DIAGNOSIS
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  • Electrocardiogram (ECG) shows runs of ≥3 PVCs with rate >100 beats/min.

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

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LABORATORY TESTS
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  • Performed if underlying causes suspected, for example:

    • MI

    • Electrolyte imbalances.

    • Digoxin toxicity.

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IMAGING
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  • ECG

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

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DIFFERENTIAL DIAGNOSIS
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DESIRED OUTCOMES

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  • Identify and correct underlying causes.

  • Resolve symptoms.

  • Prevent recurrences.

  • Avoid complications from treatment.

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TREATMENT: NONPHARMACOLOGIC THERAPY

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  • 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.

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TREATMENT: PHARMACOLOGIC ...

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