Tachyarrhythmias Study Notes

Introduction

  • Speaker: Hui Chen, a cardiologist and electrophysiologist.

  • Institution: Victorian Heart Hospital and Victorian Heart Institute.

  • Topic: Tachyarrhythmias.

  • Overview of detection methods for tachyarrhythmias.

Types of Monitors for Diagnosis

  • Tachyarrhythmias can be diagnosed using various monitoring devices:

    • Twelve lead ECG (most common for textbook cases).

    • Other devices used in clinical practice.

Sinus Tachycardia

Definition

  • Normal sinus tachycardia occurs with an underlying explanation.

Causes

Physiological Causes

  • Anxiety.

  • Acute emotions (anger, excitement).

  • Physical exertion.

  • Physiological responses lead to increased sympathetic activity, resulting in tachycardia.

Pathological Causes

  • Acute or chronic anemia.

  • Hypervolemia.

  • Heart failure post-myocardial infarction (MI).

  • Conditions increasing sympathetic activity or causing hypoxia, including:

    • Pulmonary embolism.

    • Infections.

    • Malignancy.

    • Thyrotoxicosis.

    • Pheochromocytoma.

  • List of medications that may elicit tachycardia.

Diagnostic Tools

  • Twelve lead ECG is crucial for patients suspected of sinus tachycardia.

  • Referral may occur for patients misdiagnosed with sinus tachycardia who actually have different tachyarrhythmias (e.g., focal atrial tachycardia, atrial flutter).

  • Sinoatrial (SA) node location is in the high posterior lateral aspect of the right atrium.

ECG Characteristics

  • Atrial activation in sinus rhythm yields a positive P wave in leads I and II.

  • Example ECG: Regular narrow complex tachycardia with a P wave preceding every QRS complex.

Holter Monitoring

  • Essential for differentiating normal sinus tachycardia from inappropriate sinus tachycardia.

Inappropriate Sinus Tachycardia (IST)

Definition

  • Sinus heart rate > 100 beats per minute at rest or mean heart rate > 90 beats per minute over 24 hrs, paired with palpitations.

Epidemiology

  • Approximately 1% of the population exhibits a resting heart rate > 100 bpm.

Current Understanding

  • Incomplete understanding of IST mechanisms. Hypotheses include:

    • Increased automaticity of the SA node.

    • Hypersensitivity to beta-adrenergic stimuli.

    • Decreased parasympathetic inputs.

    • A combination of these factors is likely involved.

Diagnostic Approach

  • Baseline ECG for patients suspected of IST.

  • Holter monitoring for mean heart rate determination and symptom-rhythm correlation.

  • Exclude secondary causes of sinus tachycardia.

Management Challenges

  • Management is complex; general measures include:

    • Adequate fluid intake.

    • Avoiding caffeine and energy drinks.

  • Medication: Ivabradine specifically targets the sinus node to reduce heart rate.

  • Anecdotal reports of improvement post-ablation, though not widely accepted.

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)

Definition

  • A form of supraventricular tachycardia (SVT) due to an extra electrical circuit around the AV node.

Mechanism

  • Reentrant loop forms between two circuits involving AV conduction.

  • Initial conduction travels from the sinus node to the AV node and further.

ECG Characteristics

  • Regular narrow complex tachycardia; opportunity to observe a notch in the terminal QRS in V1 indicating a retrograde P wave.

Clinical Approach

  • Symptom-rhythm correlation is critical due to the sporadic nature of AVNRT.

  • Observed in emergency situations through twelve lead ECG or smartwatch evidence.

Management

  • Conservative approach for infrequent episodes.

  • Acute management:

    • Valsalva maneuvers, especially blowing into a syringe.

    • Leg elevation during episodes.

  • Adenosine as medication of choice during acute SVT reversion.

  • Long-term management options include beta blockers and calcium channel blockers.

  • Electrophysiology (EP) study & ablation considered for persistent cases:

    • Invasive procedure, approximately 90 minutes duration, with success rate ~ 95% and 1% risk of serious adverse events.

Atrioventricular Reentrant Tachycardia (AVRT)

Definition

  • Caused by an extra electric circuit between the atrium and ventricle; can be left or right-sided.

Mechanism

  • Similar to AVNRT but involves distinct pathways; leads to reentrant loops.

    • Orthodromic AVRT: Conduction down the AV node and back up.

    • Antidromic AVRT: Conduction down an accessory pathway and back up the AV node.

ECG Characteristics

  • Normal or abnormal baseline ECG.

  • Evidence of pre-excitation (short PR interval and slurred QRS onset).

Clinical Approach

  • Symptom-rhythm correlation less relevant for patients with pre-excitation and palpitations.

Management

  • Similar to AVNRT approach.

  • Determine accessory pathway potency through stress tests or invasive EP studies.

  • Mild symptoms may only require observation.

  • Medical management less relevant; ablation is crucial for patients showing pre-excited atrial fibrillation (AF).

Pre-Excited Atrial Fibrillation

Definition

  • Caused by rapid conduction through accessory pathways, leading to hemodynamic instability.

  • Instances of hypotension, heart failure, and sudden cardiac death can occur in severe cases.

Premature Atrial Complexes (PACs)

Prevalence

  • Very common; 99% of patients >50 years show at least one PAC in 24 hours.

Risk Factors

  • Older age.

  • Increased prevalence of cardiovascular disease.

  • Inverse correlation with HDL cholesterol levels and physical activity.

Clinical Consequences

  • Higher risk of new onset atrial fibrillation, stroke, and mortality.

ECG Characteristics

  • Sinus rhythm interrupted by PACs indicated by a change in P wave morphology.

  • Atrial bigeminy may be observed.

Diagnostic Approach

  • Holter monitor for PAC burden assessment; symptom-rhythm correlation.

  • Echocardiogram to exclude structural disease.

Management

  • Symptom-based treatment; no evidence that suppression of PACs leads to better outcomes.

  • Periodic monitoring recommended due to increased AF risk.

  • Rarely consider medications or ablation for isolated PACs.

Atrial Tachycardia (AT)

Definition

  • A focal point in the atrium, not involving the sinus node, creating a fast firing rate.

Prevalence

  • Accounts for ~10% of SVT ablation cases.

  • Generally benign aside from palpitations, but may result in cardiomyopathy.

ECG Characteristics

  • Regular narrow complex tachycardia; distinguishing from reentrant SVT can be difficult.

Management

  • Conservative for infrequent symptoms; patient preference essential.

  • Medications: beta-blockers, calcium channel blockers, and flecainide.

  • Ablation is effective in managing focal atrial tachycardia.

Premature Ventricular Complexes (PVCs)

Prevalence

  • 1-2% show PVCs on a 10-second ECG; up to 12% may have a PVC after an hour of monitoring.

  • 56% have PVCs over 24 hours.

Risk Factors

  • Similar to PACs, including age, height, hypertension, smoking, and reduced left ventricular function.

Associated Risks

  • PVCs commonly lead to heart failure if burden exceeds 10%.

  • Correlation issues between PVC presence and heart failure incidence.

Diagnostic Approach

  • Detailed 12-lead ECG and Holter monitoring for PVC burden assessment.

Management

  • Conservative or pharmacotherapy as initial approaches; ablation for frequent PVCs or patients exhibiting significant symptoms.

  • Not all ablation is equal; right ventricular outflow tract PVCs are easier to treat.

Ventricular Tachycardia (VT)

Definition

  • Characterized by three or more consecutive ventricular beats at a rate of ≥100 bpm.

  • Subdivided into nonsustained (lasting <30 sec) and sustained (lasting ≥30 sec).

Etiology

  • Varies with age and gender; includes:

    • Coronary artery disease.

    • Cardiomyopathies.

    • Genetic arrhythmias (e.g., long QT syndrome).

Risks

  • Increased risk for sudden cardiac death associated with VT.

Diagnostic Approach

  • Importance of Holter monitoring for nonsustained VT detection.

  • Structural assessments critical.

Management

  • Cardioversion for sustained VT if hemodynamically compromised;

  • Beta blockers as first-line therapy for non-sustained VT management.

  • Amiodarone for PVC and VT suppression; significant long-term side effects noted.

  • Interventions include ICD implantation or ablation for patients showing resistance to medical therapies.