Tachycardia, Ventricular (VT)

Essentials of Diagnosis

• Fast, wide QRS complex on ECG

• Associated with ischemic heart disease, particularly in older patients

• In the absence of reversible cause, implantable cardioverter defibrillator (ICD) is recommended if meaningful life expectancy is longer than 1 year

General Considerations

• Defined as three or more consecutive ventricular premature beats and classified as either

  • Nonsustained: lasting < 30 seconds and terminating spontaneously or

  • Sustained: a heart rate > 100 beats/min

• VT is a frequent complication of acute myocardial infarction and dilated cardiomyopathy

  • May occur in chronic coronary disease, hypertrophic cardiomyopathy, myocarditis, and in most other forms of myocardial disease

  • Can also be a consequence of atypical forms of cardiomyopathies, such as arrhythmogenic right ventricular cardiomyopathy

  • However, idiopathic VT can also occur in patients with structurally normal hearts

• Accelerated idioventricular rhythm

  • A regular wide complex rhythm with a rate of 60–120 beats/min, usually with a gradual onset

  • Occurs commonly in acute infarction and following reperfusion with thrombolytic medications

• Torsades de pointes

  • A form of VT in which QRS morphology twists around the baseline

  • May occur in the setting of severe hypokalemia, hypomagnesemia, or after administration of a medication that prolongs the QT interval

• Palpitations

• Dyspnea

• Lightheadedness

• May be asymptomatic on rare occasion

• Patients with underlying cardiac disease or other severe comorbidities can present with syncope or cardiac arrest

• Episodes may be triggered by exercise or emotional stress

Laboratory Findings

• Comprehensive blood laboratory work should be performed as VT can occur in the setting of hypokalemia and hypomagnesemia

• Cardiac markers may be elevated when VT presents in the setting of acute myocardial infarction or as a consequence of underlying coronary artery disease and demand ischemia

Diagnostic Studies

• In patients with sustained, hemodynamically tolerated VT, a 12-lead ECG during tachycardia should be obtained

• Cardiac evaluation with echocardiography or cardiac MRI, ambulatory ECG monitoring and exercise testing may be warranted depending on the clinical situation

• In survivors of cardiac arrest or those with life-threatening ventricular arrhythmia, invasive coronary angiography is recommended to establish or exclude the presence of significant coronary artery disease

• Invasive electrophysiology (EP) study

  • No general role in patients with sustained VT who otherwise meet criteria for implantable cardioverter defibrillator (ICD)

  • May provide important information in

    • Patients with structural heart disease and syncope of unknown cause

    • Situations in which the mechanism of wide complex tachycardia is uncertain

Differentiation of Aberrantly Conducted Supraventricular Beats From Ventricular Beats

• Distinguishing VT from SVT with aberrant conduction on 12-lead ECG is important because of the differing prognostic and therapeutic implications of each type

• Ventricular origin

  • AV dissociation

  • QRS duration exceeding 0.14 second

  • Capture or fusion beats (infrequent)

  • Left axis deviation with right bundle branch block morphology

  • Monophasic (R) or biphasic (qR, QR, or RS) complexes in V₁

  • A qR or QS complex in V₆

• Supraventricular origin

  • A triphasic QRS complex, especially if there was initial negativity in leads I and V₆

  • Ventricular rates exceeding 170 beats/min

  • QRS duration longer than 0.12 second but not longer than 0.14 second

  • Presence of preexcitation syndrome

• Patients with a wide-complex tachycardia, especially those with known cardiac disease, should be presumed to have VT if the diagnosis is unclear

• The relationship of the P waves to the tachycardia complex is helpful

  • A 1:1 relationship usually means a supraventricular origin, except in the case of VT with retrograde P waves

Accelerated idioventricular rhythm

• Does not require treatment unless there is hemodynamic compromise or more serious arrhythmias

Acute VT

• A short-acting intravenous beta-blocker or verapamil may terminate the episode

• In the presence of known or suspected structural heart disease, assessment of hemodynamic stability determines the need for urgent direct current (DC) cardioversion

• Immediate synchronized DC cardioversion with 100–360 J should be performed when VT causes hypotension, heart failure, or myocardial ischemia

• Intravenous amiodarone

  • Dosage: 150 mg bolus followed by 1 mg/min infusion for 6 h and then 0.5 mg/min for 18 h

  • Indication: if VT recurs; should be administered to achieve a stable rhythm with further attempts at cardioversion as necessary

  • Side effect of rapid infusion: significant hypotension

• In patients with sustained VT who are hemodynamically stable, intravenous amiodarone, lidocaine, or procainamide can be used

• However, DC cardioversion should be performed if the VT fails to terminate or symptoms worsen

• Empiric magnesium replacement (1–2 g intravenously) may help especially for polymorphic VT

• If polymorphic VT recurs, increasing the heart rate with isoproterenol infusion (up to 20 mcg/min) or atrial pacing with a temporary pacemaker (at 90–120 bpm) effectively shortens the QT interval to prevent further episodes

Chronic VT

• Suppressive treatment with beta-blocker or a non-dihydropyridine calcium channel blocker may be tried in patients with structurally normal hearts and VT with typical outflow tract (left bundle branch block with inferior axis) or left posterior fascicle (right bundle branch block with superior axis) appearance on ECG

• Catheter ablation

  • Has a high success rate in patients who do not respond to initial medical treatment

  • Can be used as a palliative therapy for those patients with recurrent tachycardia

• ICD implantation recommended for patients with significant LV dysfunction when meaningful survival is expected to be longer than 1 year

• Beta-blockers are the mainstay for medical treatment of VT in patients with structural heart disease

• Antiarrhythmic medications

  • Have not been shown to lower mortality

  • May decrease subsequent episodes and reduce the number of ICD shocks

  • Amiodarone is generally preferred in patients with structural heart disease

  • Sotalol may be considered as well

Prognosis

• In individuals without heart disease, nonsustained VT is generally associated with a benign prognosis

• In patients with structural heart disease, nonsustained VT is associated with an increased risk of subsequent symptomatic VT and sudden death, especially when seen more than 48 hours after myocardial infarction

• In nonacute settings, most patients with VT have known or easily detectable cardiac disease and the finding of VT is an unfavorable prognostic sign

When to Refer

• Any patient with sustained VT or syncope of unknown cause in the presence of underlying structural cardiac disease