Narrow QRS Tachycardia

Introduction

  • Required Reading: Introduction to Arrhythmia Diagnosis 
  • Narrow QRS is ≤ 120ms
  • Narrow QRS = Simultaneous activation of both ventricles
    • Atrial tachycardias generally have a narrow QRS because their ventricular activation occurs via the AV node and the ventricular conduction system (His-Purkinje system), which leads to simultaneous activation of both ventricles.
    • NOTE: Atrial tachycardias can have a wide QRS, often in the presence of a RBBB, LBBB, or pre-excitation.
  • NOTE: The term “SVT – Supraventricular Tachycardia” refers to narrow-QRS REGULAR tachycardia.  Even though atrial fibrillation is “supraventricular”, it is not classically called SVT. 

The Approach

  1. Describe the ECG & Frame the Problem
    • Step 1: Narrow vs. Wide (≥120ms?)
    • Step 2: Regular vs. Irregular (use calipers)
  2. Present a differential diagnosis (see Tables)
  3. Narrow the differential diagnosis (understanding the mechanisms of arrhythmia)
DDx of an IRREGULAR narrow QRS Tachycardia:
  • Atrial Fibrillation
  • Atrial Flutter with a variable AV block
  • Multifocal Atrial Tachycardia (very rare)

NOTE: List not exhaustive, other mechanisms exist

Differential Diagnosis of a REGULAR Narrow QRS Tachycardia
  1. Sinus Tachycardia (ST)
  2. Focal Atrial Tachycardia
  3. Atrial Flutter (AFL)
  4. AV-Nodal Re-entrant Tachycardia (AVNRT)
  5. Atrioventricular Re-entrant Tachycardia (AVRT)
  6. Less Common:
    • Junctional Tachycardia (JT) 
    • Ventricular Tachycardia – Often with high-septal origin, which accesses the HIS-Purkinje system.

Approach to diagnosis

Medical students and PGY1-2 residents should make the distinction between irregular narrow complex tachycardia and regular narrow complex tachycardia (aka SVT), and should know the differential diagnosis and the initial management for each.  Distinguishing between the types of SVTs is advanced, and is unlikely to make a difference in the acute and subacute management of the arrhythmia.  

Approach to a narrow QRS tachycardia

Advanced Diagnosis of SVT

(Recommended for PGY3 and above once you have the initial understanding and approach to arrhythmias)

Types of SVT

Acute Management

  1. Stable vs. Unstable
    • Assess for hypotension, shock, altered LOC, new/worsening heart failure, ischemic chest pain.
    • If the patient is unstable, the treatment is usually synchronized cardioversion.
  2. Determine if REGULAR vs. IRREGULAR because the management is slightly different.
  3. Breathe!
    • A stable patient with a narrow QRS tachycardia is not a medical emergency.
    • Take the time to fully assess the patient, and consider treatment options below. 
    • You often don’t need the tachycardia diagnosis to treat the patient acutely, so don’t get hung up on the ECG.  
      The most important thing is to follow the approach!

NOTE: The approach to a narrow QRS tachycardia is nicely summarized in the AHA ACLS Guideline (right side)

AHA 2012 Tachycardia w Pulse Algorithm

REGULAR Narrow Complex Tachycardia (SVT)

  1. Assess ABCs
    • –> if patient is unstable (i.e. symptomatically hypotensive, evidence of ischemia/shock) –> deliver SYNCHRONIZED cardioversion
  2. Vagal Manoeuvres (Stable Patient)
    • Effectiveness 19-54%
    • Mechanism: stimulate carotid body to initiate parasympathetic response, which creates AV nodal delay/block and terminate tachycardia. 
    • Valsalva Maneuver (17% success)- internationally recognized first line
    • Modified Valsalva Maneuver  (43% success) 
      • Start semi-recumbent.  After valsalva, change position to supine and raise legs.
      • Blowing into a 10cc syringe can help ensure adequate valsalva
ESC 2019 SVT Guideline Approach
    • Carotid Massage
      • Auscultate to ensure no bruit (do not perform if prior TIA/stroke)
      • Extend neck, turn away from the side of interest.  Apply constant pressure no more than 5s.
  1. Adenosine (See section on Adenosine)
  2. Beta Blocker
    • Contraindications: hypotension and heart failure
    • PO metoprolol 25-50mg is most common- short acting and titratable. 
    • IV beta blockers 
      • Metoprolol 2.5-15 mg IV in 2.5mg boluses
      • Esmolol (0.5 mg/kg bolus or 0.05-0.3 mg/kg/min infusion)
  3. Calcium Channel Blockers
    • Contraindicated in:
      • Hemodynamic instability (hypotension)
      • Heart failure with reduced LVEF
      • Suspicion of VT (can exacerbate hypotension)
      • Pre-excited AF
    • May be more effective than beta blockers at rate control, however they have additional side effects of exaggerated hypotension and negative inotropy, which can exacerbate heart failure. 
      • Diltiazem 20mg over 2 min
      • Verapamil 5-10mg over 2 min
    • NOTE: Oral medications are preferred for safety reasons.  Only reason to use IV is if the patient is significantly symptomatic, and faster onset is preferred. 
  4. Amiodarone
    • Indications:
      • Hemodynamically unstable + refractory to cardioversion
      • Acute heart failure
    • Amiodarone IV 150mg boluses + (if needed 60 mg/hr IV infusion)
  5. Digoxin
    • Option for patients with HF and AF
    • 1 g load (0.5mg IV + 0.25 IV x2 doses q4h)

IRREGULAR Narrow Complex Tachycardia

  • Acute management is similar to REGULAR narrow complex tachycardia, with a few notable differences:
    • Generally no role for vagal maneuvers
    • Generally no role for adenosine
    • (None of the irregular NCTs on the differential diagnosis require the AV node as part of their mechanism)

Adenosine

  • Introduction:
    • Can terminate AV nodal dependent tachycardias (ones that require AV node as part of their mechanism)
    • If it does not terminate the tachycardia, the rhythm strip provides important diagnostic information (ALWAYS run a 12-lead continuous ECG strip)
  •  Indications:
    • Hemodynamically stable narrow QRS regular tachycardia
  • How to adminsiter:
    • Place the patient on cardiac monitoring (small case-report risk of AV/VF)
    • Counsel the patient on sensation of adenosine (10-20s of dyspnea and flushing).
    • Connect a 12-lead ECG – and ask the technologist to run CONTINUOUS 12-lead stip
    • Deliver 6mg IV bolus, into a proximal IV (i.e. antecubital), followed by a quick flush (many physicians use a 3-way stopcock).
  • Interpreting the result:
    • Anticipated response: AV block or pause (even for one beat)
      • If no effect, give 12mg, and 18mg if patient is agreeable.
    • Adenosine slows the sinus rate and blocks the AV node via the A1 receptor. 
    • Tachycardias that terminate and convert to sinus rhythm are called “Adenosine Sensitive”
      • Adenosine sensitive tachycardias are generally those that use the AV node as part of their circuit (AV nodal dependent). They are generally AVNRT and AVRT.
      • NOTE: In rare cases atrial tachycardia and flutter can terminate with adenosine.  Just remember that “adenosine sensitive” makes AVNRT/AVRT more likely, but does not rule out other mechanisms
      • P-waves can often be revealed, which helps determine the mechanism

Chronic Management

Chronic management depends on the mechanism of the tachycardia.

NOTE: SVT is generally a benign condition with a good prognosis.  Patients with infrequent minimally symptomatic self-limiting episodes may not need any chronic therapy. 

  • Focal Atrial Tachycardia
    • Ablation (Class 1) – EP referral
    • Medical Management
      • B-Blocker / CCB / anti-arrhythmic (propafenone or flecainide)
      • Ivabradine with beta-blocker can be considered
      • Amiodarone
  • Sinus Tachycardia
    • Treat reversible causes
    • Ivabradine or Beta-blocker can be considered in highly symptomatic cases.
  •  AVNRT
    • Catheter Ablation (Class 1) – EP referral
    • Minimally symptomatic/infrequent –> may not need therapy
    • Medical Management
      • Diltiazem or verapamil in patients without HFrEF
    • Beta blockers
  • AVRT
    • Catheter Ablation (Class 1) – EP referral
    • Medical Management
      • Orthodromic AVRT –> Beta Blocker or Diltiazem/Verapamil
      • Antidromic AVRT –> Propafenone/flecainide
  • Atrial Fibrillation and Flutter
    • Decide rate vs. rhythm control
    • Anticoagulation for stroke prevention
    • (See separate topic on atrial fibrillation)

Further Reading / References

  • ESC 2018: Supraventricular Tachycardia Guidelines (HTML

Special (Common) Cases

Narrow QRS Tachycardia and Hypotension

  • Presents a challenge because using beta-blockers and calcium channel blockers is contraindicated in patients who are hypotensive. 
  • However, slowing down the patient is important because diastolic filling is reduced in tachycardias faster than > 150bpm, and cardiac output would reduced. 
  • You have 3 options:
    1. Electrical Cardioversion – generally requires sedation (unless patient is not conscious)
    2. Amiodarone IV – Generally neutral effect on blood pressure, generally acts as a B-blocker acutely (chronically it is an anti-arrhythmic)
    3. Digoxin IV – Neutral effect on blood pressure

Narrow QRS Tachycardia and Heart Failure

  • It is often unclear if the mechanism of the heart failure is poor diastolic filling due fast tachycardia (> 150bpm), reduced LV systolic function due to chronic uncontrolled tachycardia (aka tachycardia mediated cardiomyopathy), or LV dysfunction due to another cause which caused atrial fibrillation by increasing left atrial pressure.
  • Beta blockers and calcium channel blockers are negative inotropes and are contraindicated in acute heart failure due to risk of triggering worsening pulmonary edema and cardiogenic shock.
  • 4 management options:
    1. Electrical Cardioversion – Generally requires sedation, which is challenging because the patient is hypoxemic, and sedation can reduce their respiratory drive.
    2. Amiodarone IV – Very common agent that is generally safe in patients with heart failure. 
    3. Digoxin IV – Provides mild positive inotropy, and can reduce the rate of the tachycardia (although the rate control effect is often very mild). 
    4. **Diuresis** – (Most Important) Treating the patient’s heart failure can reduce sympathetic tone and left atrial pressure, which often drive atrial and ventricular tachycardias.
  • Practical Tip – If the patient will be managed in a monitored unit, amiodarone and diuretics are used.  If the patient is on the ward, digoxin and IV diuresis may be enough for acute management.  It is not always necessary establish rate control as soon as possible. 
    • It may be acceptable to avoid overly aggressive initial rate control, and initiate IV diuretics, which will improve the patient’s rate over time by treating their heart failure.

Contributors

  • Author: Dr. Pavel Antiperovitch MD FRCPC 
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