The advent of the implantable cardioverter-defibrillator (ICD) has changed the face of ventricular arrhythmia management. Like pacemakers, these devices can be implanted transvenously in a brief, low-risk procedure. Once implanted, the ICD can detect ventricular tachyarrhythmias and terminate them with defibrillation shocks or anti-tachycardia pacing algorithms (see the image below).
Termination of ventricular tachycardia (VT) with overdrive pacing. This patient has reentrant VT, which is terminated automatically by pacing from an implantable cardioverter-defibrillator.
ICD therapy is used to augment medical management for the following individuals [4] :
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Most patients with hemodynamically unstable VT
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Most patients with prior myocardial infarction (MI) and hemodynamically stable sustained VT
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Most cardiomyopathy patients with unexplained syncope (an arrhythmia is presumed)
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Most patients with genetic sudden death syndromes when unexplained syncope is noted
In patients with prior VT or ventricular fibrillation (VF), the Antiarrhythmics Versus Implantable Defibrillators (AVID) study, the Canadian Implantable Defibrillator Study (CIDS), and the Cardiac Arrest Study, Hamburg (CASH), demonstrated better survival with ICD therapy than with antiarrhythmic therapy with amiodarone or sotalol. [77] The survival difference was statistically significant in AVID, of borderline significance in CIDS, and insignificant in CASH. A meta-analysis of the three trials found a 28% reduction in relative risk of death. [77]
Patients with nonischemic dilated cardiomyopathy and considerable left ventricular dysfunction, or arrhythmogenic right ventricular cardiomyopathy, who have sustained VT or VF should have ICD placement. These patients should also be receiving optimal long-term medical therapy and may reasonably be expected to survive with good functional status for longer than 1 year. [4]
ICDs are not used for the following individuals [46] :
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Patients with VT or VF occurring during an acute ST-segment elevation MI (STEMI)
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Patients with reversible, drug-induced VT
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Patients with poor expected survival as a consequence of comorbid conditions
Because ICDs treat, rather than prevent, ventricular arrhythmias, as many as 50% of ICD recipients require therapy with antiarrhythmic drugs to reduce the potential for ICD shocks. Catheter ablation may be used in patients with an ICD who are receiving multiple shocks because of sustained VT that is not manageable by changing drug therapy or who do not wish to undergo long-term drug therapy. [40]
Prospective follow-up data from 2,352 patients in the Israeli ICD Registry suggest that the presence of anemia (hemoglobin [Hb] ≤12 g/dL) in patients with ICDs independently increases the risk for ventricular arrhythmias during long-term follow-up. [78] At 2.5 years of follow-up, the rate of appropriate shocks in patients with low Hb levels (11%) was nearly double that of those with high Hb levels (6%) (log-rank P <0.005). Moreover, each 1 g/dL reduction in Hb was independently associated with a significant 8% increased risk for a first appropriate shock (P <0.03), and anemia increased the risk for all-cause mortality as well as heart failure hospitalizations or death, but not with inappropriate ICD shocks. [78]
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This electrocardiogram (ECG) shows rapid monomorphic ventricular tachycardia (VT), 280 beats/min, associated with hemodynamic collapse. The tracing was obtained from a patient with severe ischemic cardiomyopathy during an electrophysiologic study. A single external shock subsequently converted VT to sinus rhythm. The patient had an atrial rate of 72 beats/min (measured with intracardiac electrodes; not shown). Although ventriculoatrial dissociation (faster V rate than A rate) is diagnostic of VT, surface ECG findings (dissociated P waves, fusion or capture beats) are present in only about 20% of cases. In this tracing, the ventricular rate is simply too fast for P waves to be observed. VT at 240-300 beats/min is often termed ventricular flutter.
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This electrocardiogram shows slow monomorphic ventricular tachycardia (VT), 121 beats/min, from a patient with an old inferior wall myocardial infarction and well-preserved left ventricular (LV) function (ejection fraction, 55%). The patient presented with symptoms of palpitation and neck fullness. Note the ventriculoatrial dissociation, which is most obvious in leads V2 and V3. Slower VT rates and preserved LV function are associated with better long-term prognosis.
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At first glance, this tracing suggests rapid polymorphic ventricular tachycardia. It is actually sinus rhythm with premature atrial complex and a superimposed lead motion artifact. Hidden sinus beats can be observed by using calipers to march backward from the final two QRS complexes. This artifact can be generated easily with rapid arm motion (eg, brushing teeth) during telemetry monitoring.
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Torsade de pointes. Image A: This is polymorphic ventricular tachycardia associated with resting QT-interval prolongation. In this case, it was caused by the class III antiarrhythmic agent sotalol. This rhythm is also observed in families with mutations affecting certain cardiac ion channels. Image B: Torsade de pointes, a form of ventricular tachycardia. Courtesy of Science Source/BSIP.
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Preexcited atrial fibrillation. The patient has an accessory atrioventricular connection. Atrial fibrillation has been induced. Conduction over an accessory pathway results in a wide QRS complex, mimicking ventricular tachycardia.
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Curative ablation of ventricular tachycardia (VT). The patient had VT in the setting of ischemic cardiomyopathy. VT was induced in an electrophysiology laboratory, and an ablation catheter was placed at the critical zone of slow conduction within the VT circuit. Radiofrequency (RF) energy was applied to tissue through the catheter tip, and VT was terminated when the critical conducting tissue was destroyed.
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Ventricular pacing at 120 beats/min. Newer pacemakers use bipolar pacing. If a smaller pacing stimulus artifact is overlooked, an erroneous diagnosis of ventricular tachycardia may result. Because leads are most commonly placed in the right ventricular apex, paced beats will have a left bundle-branch block morphology with inferior axis. Causes of rapid pacing include (1) tracking of atrial tachycardia in DDD mode, (2) rapid pacing due to the rate response being activated, and (3) endless loop tachycardia. Application of a magnet to the pacemaker will disable sensing and allow further diagnosis. Sometimes “pacing spike detection” must be programmed “ON” in the electrocardiographic system to make the spike apparent.
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Supraventricular tachycardia with aberrancy. This tracing is from a patient with a structurally normal heart who has a normal resting electrocardiogram. This rhythm is orthodromic reciprocating tachycardia with rate-related left bundle-branch block. Note the relatively narrow RS intervals in the precordial leads.
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Termination of ventricular tachycardia (VT) with overdrive pacing. This patient has reentrant VT, which is terminated automatically by pacing from an implantable cardioverter-defibrillator.
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Posteroanterior view of a right ventricular endocardial activation map during ventricular tachycardia in a patient with a previous septal myocardial infarction. The earliest activation is recorded in red, and late activation as blue to magenta. Fragmented low-amplitude diastolic local electrograms were recorded adjacent to the earliest (red) breakout area, and local ablation in this scarred zone (red dots) resulted in termination and noninducibility of this previously incessant arrhythmia.
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This tracing depicts monomorphic ventricular tachycardia.
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This image demonstrates polymorphic ventricular tachycardia.
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This electrocardiogram is from a 32-year-old woman with recent-onset heart failure and syncope.
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This electrocardiogram is from a 48-year-old man with wide-complex tachycardia during a treadmill stress test. Any wide-complex tachycardia tracing should raise the possibility of ventricular tachycardia, but closer scrutiny confirms left bundle-branch block conduction of a supraventricular rhythm. By Brugada criteria, RS complexes are apparent in the precordium (V2-V4), and the interval from R-wave onset to the deepest part of the S wave is shorter than 100 ms in each of these leads. Ventriculoatrial dissociation is not seen. Vereckei criteria are based solely upon lead aVR, which shows no R wave, an initial q wave width shorter than 40 ms, and no initial notching in the q wave. The last Vereckei criterion examines the slope of the initial 40 ms of the QRS versus the terminal 40 ms of the QRS complex in lead aVR. In this case, the initial downward deflection in lead aVR is steeper than the terminal upward deflection, yielding Vi/Vt ratio above 1. All of these criteria are consistent with an aberrantly conducted supraventricular tachycardia. Gradual rate changes during this patient's treadmill study (not shown here) were consistent with a sinus tachycardia mechanism.
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The electrocardiogram shows a form of idiopathic ventricular tachycardia (VT) seen in the absence of structural heart disease. This rhythm arises from the left ventricular septum and often responds to verapamil. Upon superficial examination, it appears to be supraventricular tachycardia with bifascicular conduction block. Closer examination of lead V1 shows narrowing of fourth QRS complex, consistent with fusion between the wide QRS complex and the conducted atrial beat, confirming atrioventricular dissociation and a VT mechanism.
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A wide QRS complex tachycardia is evident on this electrocardiogram from a 64-year-old man with history of previous myocardial infarction (MI) and syncope. In patients with a prior MI, the most common mechanism of wide QRS complex tachycardia is ventricular tachycardia.
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This tracing depicts atrioventricular dissociation.
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Fusion beats, capture beats, and atrioventricular dissociation can be seen on this electrocardiogram.
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Note the retrograde P waves in this electrocardiogram.
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Retrograde P waves are also observed in this electrocardiogram.
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This electrocardiogram reveals torsade de pointes.
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Hematoxylin and eosin stain; intermediate power of a healed myocardial infarct. Note the areas of fibrosis (pale pink) dissecting between the myocytes (red).
