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Accelerated Idioventricular Rhythm (AIVR)

Article written and reviewed by Dr Luca Moretti

Accelerated idioventricular rhythm (AIVR) is a form of ventricular tachycardia originating from an ectopic focus in the ventricles. This focus begins to generate impulses faster than the normal idioventricular rhythm, with a frequency that can exceed 60 bpm, reaching 100-120 bpm. AIVR is typically an episodic arrhythmia, occurring mainly in acute situations such as during a myocardial infarction or in the presence of other structural cardiac alterations, but it can also be observed in chronic conditions in some patients with structural heart diseases.

Etiology and Pathogenesis

AIVR is caused by a dysfunction of the ventricular conduction system, leading to the formation of an ectopic focus in the ventricles. This phenomenon is generally compensatory, activated when the sinoatrial node fails to maintain the rhythm and the ventricular electrical conduction takes over.

The main etiological causes of AIVR include:

• Acute myocardial infarction: ischemic damage and necrosis of myocardial tissue alter the heart's electrical conduction and can trigger the formation of ectopic foci in the ventricles, causing AIVR.
• Cardiomyopathies and heart failure: structural heart diseases, such as dilated cardiomyopathy or heart failure, can predispose to the formation of ectopic foci in the ventricles, as ventricular dysfunction alters the normal electrical activity of the heart, favoring the onset of arrhythmias.

Pathophysiological Mechanisms

AIVR originates from a ventricular electrical dysfunction, where the ventricles begin to generate an accelerated beat due to an ectopic focus. This pathophysiological mechanism is often a compensation when the sinoatrial node fails to control the rhythm. Ionic imbalances, such as alterations in potassium or magnesium concentration, can affect the repolarization of myocardial cells and predispose to the formation of these ectopic foci. Additionally, a wide QRS, which appears during the AIVR episode, is a distinctive sign, as the beat does not follow the normal conduction pathway through the atrioventricular node and the His bundle.

Following these phenomena, the ventricular rate accelerates beyond normal, generating an irregular rhythm that can be dangerous in cases of hemodynamic instability. The presence of a wide QRS is useful for differentiating AIVR from other arrhythmias, such as sustained ventricular tachycardia, which has similar characteristics but a different genesis.

Risk Factors

The risk of developing an accelerated idioventricular rhythm (AIVR) is higher in patients with conditions that predispose to cardiac dysfunctions or alterations in electrical conduction. These factors are not direct causes but represent conditions that increase the likelihood of developing AIVR. The main risk factors include:

• Female sex: women, especially postmenopausal, have a greater predisposition to electrolyte imbalances that can favor AIVR.
• Advanced age: with age, the heart becomes more vulnerable to pathologies such as cardiomyopathies and heart failure, which can predispose to AIVR.
• Use of QT-prolonging drugs: medications such as certain antidepressants, antiarrhythmics, and antibiotics can alter heart repolarization and predispose to AIVR.
• Smoking and alcoholism: alcohol abuse and smoking damage the heart and promote alterations in the heart's electrical conduction, increasing susceptibility to AIVR.
• Family history of heart disease: a genetic predisposition or a history of sudden cardiac death in the family can increase the risk of developing AIVR.

Clinical Presentation

Accelerated idioventricular rhythm (AIVR) can manifest with a wide range of symptoms and objective signs, varying depending on the duration and severity of the arrhythmia. Although in some cases it may be asymptomatic, AIVR tends to produce symptoms related to reduced hemodynamic perfusion, resulting from the accelerated ventricular beat that does not allow adequate heart filling.

The main symptoms include:

• Palpitations: the patient perceives an acceleration of the heartbeat, which can be felt as an irregular or strong beat in the chest or neck. Palpitations are one of the most common signs of AIVR and may be accompanied by a feeling of anxiety or discomfort.
• Dizziness and vertigo: when the ventricular rate increases, cardiac output may decrease, causing reduced cerebral perfusion. This leads to a feeling of instability, vertigo, and dizziness, which are more evident during physical activity or with rapid movements.
• Syncope: in more severe cases, the acceleration of the ventricular beat can significantly compromise cerebral perfusion, leading to sudden loss of consciousness. Syncope is more frequent in patients with cardiac comorbidities or in cases of more persistent arrhythmias.
• Chest pain: although less frequent, chest pain can occur, especially in patients with pre-existing coronary artery disease. The pain is usually less intense than angina pectoris but may be associated with myocardial ischemia when coronary perfusion is compromised by the accelerated rhythm.

The severity of symptoms depends on the heart rate and the presence of cardiac comorbidities. In patients with pre-existing heart failure or cardiomyopathies, AIVR can further worsen the clinical picture, leading to signs of hemodynamic instability.

Among the objective signs that can be detected during an AIVR episode are:

• Irregular and rapid pulse: during the AIVR episode, the pulse may appear irregular and increased in frequency. The accelerated ventricular rate can make it difficult to palpate a regular pulse, as the beats are disorganized.
• Peripheral hypoperfusion: low cardiac output can lead to reduced blood perfusion to the extremities, which may manifest as weak and cold peripheral pulses. In some cases, a pale skin color can be observed due to poor circulation.
• Hypotension: in patients with hemodynamic instability, the arrhythmia can significantly reduce blood pressure. Severe hypotension can cause symptoms such as weakness, dizziness, and a feeling of fainting.
• Neurological alterations: when cerebral perfusion is compromised, patients may develop neurological signs such as confusion, disorientation, or even brief loss of consciousness. These symptoms are typical of transient cerebral insufficiency caused by inadequate perfusion during the arrhythmia.

  In general, AIVR symptoms and signs can vary widely depending on heart rate and episode duration. In patients with heart failure or other structural heart diseases, the arrhythmia can increase symptom severity and lead to complications such as peripheral edema or cardiogenic shock.

  Diagnosis

  The diagnosis of accelerated idioventricular rhythm (AIVR) is primarily based on a thorough clinical evaluation, supported by instrumental investigations. The electrocardiogram (ECG) is the main diagnostic tool, but in some cases, additional investigations may be necessary to confirm the diagnosis and determine the underlying cause.

  Electrocardiogram (ECG)

  During an AIVR episode, the ECG shows distinctive features, including:

  • Accelerated ventricular rate: a rate of 100–120 bpm is a distinguishing feature of AIVR, with a regular RR interval.
  • Wide QRS: the QRS complex appears broad and widened, generally lasting more than 120 ms. This is because the ectopic focus does not follow the normal conduction pathway.
  • Variable QRS morphology: the shape of the QRS complexes may vary during the episode, depending on the position of the ectopic focus within the ventricles.
  • Absence of P waves: the P wave is generally absent, as the rhythm originates in the ventricles rather than the sinoatrial node.
  
  

  A baseline ECG is usually sufficient to diagnose AIVR, but in some cases of intermittent arrhythmias or in patients with atypical symptoms, long-term monitoring using a Holter monitor may be useful.

  Differential Diagnosis

  AIVR must be distinguished from other ventricular arrhythmias and from conditions that may mimic a syncopal episode. The main conditions to consider include:

  • Polymorphic ventricular tachycardia: characterized by variable QRS morphology but with a longer duration and a more irregular arrhythmic pattern.
  • Ventricular fibrillation: disorganized, chaotic electrical activity with no recognizable QRS pattern.
  • Autonomic system disorders: neurological or vasovagal conditions that can cause syncope, such as epileptic seizures or neurocardiogenic syncope.

  Treatment

  The treatment of AIVR depends on the patient’s hemodynamic stability and the underlying cause. In cases of acute and symptomatic AIVR, treatment must be timely and aimed at resolving the arrhythmia and preventing more serious complications, such as ventricular fibrillation.

  Acute Management

  In patients with symptomatic AIVR, therapeutic measures depend on the severity of symptoms and hemodynamic stability:

  • Unstable patients (hypotension, syncope, cardiac arrest): electrical cardioversion is the first-line treatment. If the arrhythmia is severe, synchronized shock starting at 100–200 J may be necessary.
  • Stable patients: in stable cases, pharmacologic treatment is preferred, using antiarrhythmics such as lidocaine or procainamide, which help restore sinus rhythm.

  Long-term Management

  To prevent AIVR recurrence, long-term treatment focuses on controlling underlying causes and improving the patient’s cardiac stability:

  • Control of risk factors: it is essential to monitor and adequately treat conditions predisposing to AIVR, such as cardiomyopathies, heart failure, and electrolyte imbalances.
  • Antiarrhythmic medications: in some cases, chronic treatment with antiarrhythmic drugs such as beta-blockers or amiodarone may be necessary to prevent future episodes.
  • Implantable devices: in patients at high risk of recurrence, implantation of an implantable cardioverter-defibrillator (ICD) may be indicated to prevent severe arrhythmic episodes such as ventricular fibrillation.

  Prognosis

  The prognosis of AIVR depends mainly on the underlying cause and the timeliness of treatment. In patients with heart failure or dilated cardiomyopathy, the risk of recurrence is higher, and the arrhythmia can further impair cardiac function. However, if properly treated, AIVR generally has a favorable prognosis, especially in patients without significant comorbidities.

  In patients with congenital long QT or pre-existing coronary artery disease, the risk of complications such as ventricular fibrillation is higher, so regular monitoring and appropriate treatment are essential to prevent fatal outcomes.

  Complications

  Although generally a benign condition, accelerated idioventricular rhythm (AIVR) can evolve into more serious situations if not properly treated. The main complications include:

  • Ventricular fibrillation: the most feared complication, ventricular fibrillation can occur when AIVR persists and loses its characteristic pattern. The heart’s electrical activity becomes chaotic, leading to cardiac arrest if not treated promptly.
  • Cardiogenic shock: in patients with pre-existing heart failure, AIVR can further reduce the heart's ability to pump blood, leading to severe hypotension and multi-organ failure. In such cases, prompt treatment is essential to avoid irreversible organ damage.
  • Pulmonary edema: reduced cardiac perfusion and inadequate ventricular blood ejection can lead to fluid accumulation in the lungs, causing respiratory distress and requiring assisted ventilation.
  • Arrhythmic recurrence: in patients with chronic AIVR or uncontrolled electrolyte imbalances, arrhythmic recurrences can lead to progressive cardiac instability and a continuous need for long-term monitoring and treatment.

  Regular monitoring and prompt management are crucial to reducing the risk of these complications, particularly in high-risk patients such as those with dilated cardiomyopathy or heart failure.

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