Skip to content
Download PDF

Focal AtrialTachycardia

Chapter 255 | Part 12: Endocrinology · Part 6 – Cardiovascular Disorders · Chapter 255

Key Clinical Points

  1. Focal AT accounts for ~10% of paroxysmal supraventricular tachycardia (PSVTs) in patients referred for catheter ablation.
  2. Mechanisms include abnormal automaticity, triggered automaticity, or small reentry circuits in diseased atrial tissue.
  3. AT is not dependent on AV nodal conduction; therefore, the atrial rate remains unaffected by AV block and AT will not terminate with AV block.
  4. A 'warm-up' phase (atrial rate increases after initiation) or 'cool-down' phase (rate slows before termination) favors a diagnosis of AT over AV nodal-dependent SVTs.
  5. P-waves in AT are typically discrete with an intervening isoelectric segment, distinguishing them from atrial flutter and macroreentrant AT.
  6. AT can occur without structural heart disease but is often associated with atrial fibrosis (e.g., post-ablation) or sympathetic stimulation.
  7. AT with AV block is a specific indicator of digitalis toxicity.
  8. Asymptomatic nonsustained AT identified on ambulatory monitoring does not require treatment.
  9. P-wave morphology varies by location: e.g., atrial septum (narrower duration), left atrium (monophasic, positive in V; negative in I and aVL).
  10. Treatment must be tailored to the underlying condition: sinus node modification is ineffective for POTS and may worsen non-tachycardia components; blood pressure-increasing drugs are inappropriate for inappropriate sinus tachycardia.

DEFINITION & OVERVIEW

• Definition: Focal atrial tachycardia (AT) is a form of supraventricular tachycardia originating from a discrete focus within the atria. • Terminology: The term 'focal' distinguishes AT from typical/atypical atrial flutter but does not define the specific mechanism. • Clinical Presentation: Can be sustained, nonsustained, paroxysmal, or incessant. • Prevalence: Accounts for approximately 10% of PSVTs in patients referred for catheter ablation. • Observation: Nonsustained AT is common on ambulatory ECG recordings; prevalence increases with age. Asymptomatic cases are often labeled 'SVT' but do not require treatment.

Mechanisms of Focal AT

• Primary Mechanisms: ◦ Abnormal automaticity ◦ Triggered automaticity ◦ Small reentry circuit in diseased atrial tissue • AV Conduction Patterns: ◦ Typically 1:1 AV conduction. ◦ May present with AV block (Wenckebberg or fixed, e.g., 2:1 or 3:1). • Diagnostic Indicators: ◦ Atrial rate unaffected by AV block → distinguishes AT from AV nodal-dependent SVTs. ◦ Warm-up phase (rate increases after initiation) or cool-down phase (rate slows before termination) → favors AT due to enhanced automaticity.

EPIDEMIOLOGY

• Clinical Context: ◦ ~10% of PSVTs in patients referred for catheter ablation. ◦ Frequently identified on ambulatory ECG recordings; prevalence increases with age. • Management Rule: ◦ Asymptomatic nonsustained ATs labeled as 'SVT' on monitors → treatment is not recommended.

ETIOLOGY & PATHOPHYISIOLOGY

• Structural Factors: ◦ Can occur in the absence of structural heart disease. ◦ Associated with atrial fibrosis (e.g., from prior catheter ablation). ◦ Fibrotic areas act as a nidus for automaticity from injured but partially living cells. • Other Drivers: ◦ Microreentry in zones of slow conduction within/on the border of fibrotic areas. ◦ Sympathetic stimulation is a promoting factor. • Clinical Indicators: ◦ AT can signal underlying illness or drug toxicity. ◦ AT with AV block → characteristic of digitalis toxicity.

CLINICAL FEATURES

• Symptom Variability: Highly variable; similar to other SVTs. • Incessant AT: Can lead to tachycardia-induced cardiomyopathy.

ECG Findings

• P-wave Characteristics: ◦ Often discrete with an intervening isoelectric segment (unlike atrial flutter/macroreentrant AT). ◦ Morphology varies by location of the focus. • Location-Specific Morphologies: ◦ Atrial septum → narrower P-wave duration than sinus rhythm. ◦ Left atrium → monophasic, positive P wave in lead V; negative P waves in I and aVL. ◦ Superior locations (SVC/superior pulmonary veins) → positive in inferior leads (II, III, aVF). ◦ Inferior location (ostium of coronary sinus) → negative P waves in II, III, and aVF. ◦ Crista terminalis (near sinus node) → resembles sinus tachycardia. • Timing: ◦ Abrupt onset/offset favors AT over sinus tachycardia. ◦ At high rates, P-wave may fall on T-wave or during 2:1 conduction.

DIFFERENTIAL DIAGNOSIS

• Sinus Tachycardia: ◦ AT distinguished by P-wave morphology. ◦ In 1:1 conduction, AT typically has a shorter P-R interval than R-P interval (due to rapid AV nodal conduction). ◦ Abrupt onset/offset favors AT. • AV Nodal-Dependent SVTs (AVNRT, AVRT): ◦ AT does not terminate with AV block; atrial rate remains constant during block. • Atrial Flutter / Macroreentrant AT: ◦ AT has discrete P-waves with isoelectric segments; flutter/macroreentry do not. • Inappropriate Sinus Tachycardia (IST) / POTS: ◦ Recognition of these distinct clinical syndromes is critical for treatment selection.

R-P Relationships

• AT: R-P > P-R • AV node reentry (uncommon form): R-P > P-R

INVESTIGATIONS & DIAGNOSIS

• Ambulatory ECG Monitoring: ◦ Common for identifying nonsustained AT. ◦ Prevalence increases with age. • ECG Analysis: ◦ Identify P-wave morphology (location-specific). ◦ Assess for AV block response (AT remains constant). ◦ Look for warm-up/cool-down phases. • Drug Toxicity Screening: ◦ AT with AV block → suspect digitalis toxicity.

Diagnostic Criteria

• Focal AT Diagnosis requires: ◦ Sustained or nonsustained atrial tachycardia. ◦ P-wave morphology differing from sinus. ◦ Absence of AV nodal dependence (atrial rate unaffected by AV block). ◦ Presence of warm-up/cool-down phases.

Diagnostic Algorithm

  1. Identify atrial tachycardia on ECG.
  2. Assess P-wave morphology to determine focus location.
  3. Evaluate for AV nodal dependence (AT will not terminate with AV block).
  4. Look for warm-up or cool-down phase → favors AT over AV nodal-dependent SVT.
  5. Consider underlying causes (fibrosis, digitalis toxicity, etc.).
  6. Determine if treatment is indicated based on symptoms.

Differentiation of PSVT Mechanisms (based on R-P vs P-R relationship): 1. Observe R-P interval relative to P-R. 2. If RP < PR (typically < 120 ms) → Identify as AVNRT or AVRT (fast). 3. If RP > PR (typically > 120 ms) → Determine if Focal AT, AVRT, or Slow AVNRT (uncommon form of AVNRT).

MANAGEMENT & TREATMENT

  1. Implement strategy to reduce symptoms.
  2. Catheter Ablation: ◦ Target areas of fibrosis or automaticity. ◦ Note: Focal AT accounts for ~10% of PSVTs in ablation candidates.
  3. Targeted Management based on underlying cause: ◦ Digitalis Toxicity: → Discontinue digitalis and manage toxicity. ◦ POTS: → Avoid sinus node modification (ineffective; may exacerbate non-tachycardia components). ◦ Inappropriate Sinus Tachycardia: → Avoid treatment aimed at increasing blood pressure.

Treatment Limitations

• Sinus node modification: Ineffective for POTS; may worsen non-tachycardia components. ◦ Blood pressure medications: Not appropriate for inappropriate sinus tachycardia.

PROGNOSIS & COMPLICATIONS

• Tachycardia-Induced Cardiomyopathy: Risk associated with incessant AT. • Arrhythmia Progression: ◦ Frequent atrial ectopy and nonsustained AT are precursors to atrial fibrillation or atrial flutter. • Clinical Significance: ◦ Emergence of AT may signal underlying illness or drug toxicity.

Tachycardia-Induced Cardiomyopathy

• Incessant AT can cause tachycardia-induced cardiomyopathy; requires management to reduce symptoms.

Progression to Other Arrhythmias

• Frequent atrial ectopy and nonsustained AT are often precursors to more significant arrhythmias (atrial fibrillation, atrial flutter).

SPECIAL CONSIDERATIONS

• Digitalis Toxicity: ◦ Characterized by AT with AV block. ◦ Requires immediate discontinuation of digitalis. • POTS: ◦ Sinus node modification is contraindicated as it may worsen non-tachycardia components. • Inappropriate Sinus Tachycardia: ◦ Treatment aimed at increasing blood pressure is inappropriate.

KEY PEARLS & CLINICAL TRAPS

• AV Block Rule: AT will not terminate with AV block; atrial rate remains constant → distinguishes it from AV nodal-dependent SVTs. • Morphology: Discrete P-waves with isoelectric segments distinguish focal AT from flutter/macroreentrant AT. • Dynamics: Warm-up and cool-down phases favor a diagnosis of AT. • Toxicity: AT with AV block is a hallmark of digitalis toxicity. • Symptomless AT: No treatment recommended for asymptomatic nonsustained AT on monitors. • POTS/IST: Recognition of these specific conditions is critical to avoid inappropriate treatments (sinus node modification or BP-increasing meds).