Sandbox/NCT

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hilda Mahmoudi M.D., M.P.H.^[2]; Twinkle Singh, M.B.B.S. [3]; Rim Halaby, M.D. [4]

Narrow Complex Tachycardia Resident Survival Guide Microchapters
Overview
Causes
Diagnosis
Treatment
Do's
Don'ts

Overview

Narrow complex tachycardia (NCT) is characterized by heart rate > 100 beats per minute and QRS complex of duration < 120 milliseconds. The NCT may originate in the sinus node, the atria, the AV node, the His bundle, or combination of these tissues causing rapid activation of the ventricles. Diagnosis of NCT is established by surface ECG in correlation with history and physical examination. Hemodynamically unstable patients should receive urgent cardioversion.

Causes

Life Threatening Causes

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• Wolff-Parkinson-White syndrome
• VT

Common Causes

• Atrial fibrillation
• Atrial flutter
• Atrial tachycardia
• AVNRT
• AVRT

Diagnosis

Shown below is an algorithm summarizing the approach for diagnosing narrow complex tachycardia according to the 2003 ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias. ECG: electrocardiogram; SVT: supraventricular tachycardia; ms: Milliseconds; bpm: beats per minute; NCT: Narrow complex tachycardia

Characterize the symptoms: ❑ Asymptomatic (most common presentation) ❑ Palpitations ❑ Dyspnea ❑ Fatigue ❑ Chest discomfort ❑ Lightheadedness ❑ Syncope ❑ Polyuria <br

Identify possible triggers: ❑ Infection ❑ Caffeine ❑ Alcohol ❑ Nicotine ❑ Recreational drugs ❑ Hypovolemia ❑ Hyperthyroidism ❑ Hypoxia ❑ Acidosis ❑ Hypokalemia ❑ Hyperkalemia ❑ Hypoglycemia ❑ Hypothermia ❑ Toxins ❑ Pulmonary embolism ❑ Coronary thrombosis ❑ Trauma

Differential Diagnosis of NCT ❑ AV nodal reentrant tachycardia (AVNRT) ❑ Atrioventricular reentrant tachycardia (AVRT) ❑ Junctional tachycardia ❑ Sinus tachycardia ❑ Inappropriate sinus tachycardia ❑ Sinus node re-entry tachycardia ❑ Intraatrial reentrant tachycardia (IART) ❑ Atrial tachycardia ❑ Multifocal atrial tachycardia ❑ Atrial fibrillation ❑ Atrial flutter

Examine the patient: General appearance ❑ Well appearing Vitals ❑ Pulse ❑ Rate ❑ Tachycardia ❑ Rhythm ❑ Regular ❑ Regular irregular ❑ Irregularly irregular ❑ Strength ❑ Weak ❑ Alternating in strength ❑ Respiration ❑ Tachypnea ❑ Blood pressure ❑ Hypotension (in hemodynamically unstable patients) Neck ❑ Absent a wave in jugular venous pressure (in atrial fibrillation) Cardiovascular examination ❑ Auscultation ❑ Heart sounds ❑ Rapid regular or irregular rhythm (depending on the type of arrhythmia) ❑ Murmurs (depending on the underlying cardiac disease such as aortic stenosis)

❑ Assess hemodynamic stability ❑ Monitor the blood pressure ❑ Monitor the heart rate ❑ Order and monitor the ECG ❑ Perform urgent cardioversion in unstable patients in which the rhythm is not sinus tachycardia ❑ Give oxygen if needed

Narrow QRS tachycardia ❑ Heart rate > 100 beats/min ❑ QRS duration < 120 ms

❑ Determine the regularity of rhythm

Regular rhythm

Irregular rhythm

Consider the following causes: ❑ AVRT ❑ AVNRT ❑ Atypical AVNRT ❑ Atrial tachycardia ❑ Atrial flutter

Consider the following causes: ❑ Atrial fibrillation ❑ Atrial tachycardia/flutter with variable AV conduction ❑ MAT

❑ Determine P wave morphology

❑ Determine P wave morphology

❑ P waves are not visible

❑ P waves are visible

❑ > 3 P wave morphologies

❑ Absent P waves

❑ Sawtooth appearance of P waves

❑ Consider AVNRT

❑ Determine if atrial rate is greater than ventricular rate

MAT

Atrial fibrillation

Atrial flutter

Atrial rate > ventricular rate

Atrial rate ≤ ventricular rate

Consider the following causes: ❑ Atrial flutter ❑ Atrial tachycardia

❑ Determine if RP interval > PR interval

RP < PR

RP > PR

❑ Determine the duration of RP interval

Consider the following causes: ❑ Atrial tachycardia ❑ PJRT ❑ Atypical AVNRT

< 70 ms

> 70 ms

Consider the following cause: ❑ AVNRT

Consider the following causes: ❑ AVRT ❑ AVNRT ❑ Atrial tachycardia

Identification of the Rhythm on ECG

Shown below is an algorithm summarizing the approach to differentiate various types of narrow complex tachycardia according to the 2003 guidelines issued by ACC/AHA/ESC for the management of patients with supraventricular arrhythmias.
Abbreviations: AV: atrioventricular; AVNRT: atrioventricular nodal reciprocating tachycardia; MAT: multifocal atrial tachycardia; ms: milliseconds; PJRT: permanent form of junctional reciprocating tachycardia

Note: Patients with focal junctional tachycardia may mimic the pattern of slow-fast AVNRT and may show AV dissociation and/or marked irregularity in the junctional rate.

Treatment

Initial Approach

Shown below is an algorithm summarizing the initial approach for narrow complex tachycardia according to the 2003 ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias.

Assess the hemodynamic stability of the patient

❑ Unstable patient

❑ Stable patient

❑ If the rythm isn't sinus tachycardia: Urgent cardioversion

❑ If the rythm is sinus tachycardia: ❑ Control the rate: ❑ IV metoprolol (2.5 to 5 mg over 2 minutes up to a maximum of 15 mg). ❑ Treat the underlying cause

Documented arrhythmia

Undocumented arrhythmia (ECG is normal)

❑ Identify the specific type of NCT based on the ECG findings ❑ Treat accordingly

History suggestive of extra premature beats ❑ Sensation of a pause followed by a strong heart beat OR ❑ Irregularities in heart rhythm

History suggestive of paroxysmal arrhythmia ❑ Regular palpitations with sudden onset and termination

Rule out the following: ❑ Caffeine ❑ Alcohol ❑ Nicotine ❑ Recreational drugs ❑ Hyperthyroidism

❑ Refer for an invasive electrophysiological study AND/OR ❑ Catheter ablation ❑ Educate about vagal maneuvers ❑ Consider beta blocker

Short Term Treatment of SVT in a Hemodynamically Stable Patient

Shown below is an algorithm summarizing the management of narrow complex tachycardia according to the 2003 ACC/AHA/ESC guidelines for the management of patients with supraventricular arrhythmias.
Abbreviations: AF: atrial fibrillation; AV: atrioventricular; AVNRT: atrioventricular nodal reciprocating tachycardia; AVRT: atrioventricular reciprocating tachycardia; BBB: bundle-branch block; ECG: electrocardiography; IV: intravenous; LV: left ventricle; SVT: supraventricular tachycardia; VT: ventricular tachycardia

Acute management: ❑ Perform vagal maneuvers (Class I, level of evidence B) ❑ Valsalva maneuver ❑ Carotid massage ❑ Monitor ECG continuously

If vagal maneuvers fail: ❑ Administer IV adenosine† (Class I, level of evidence A) ❑ First dose: 6 mg rapid IV push, followed by 20 mL of normal saline bolus ❑ Second dose: 12 mg (if no response in 1-2 min) ❑ Monitor ECG continuously

❑ Assess changes on ECG following adenosine administration Changes on ECG Possible causes No change ❑ Inadequate delivery of the medication ❑ Inadequate dose ❑ VT Gradual slowing then re-acceleration of rate ❑ Sinus tachycardia ❑ Focal AT ❑ Nonparoxysmal junctional tachycardia Abrupt termination ❑ AVNRT ❑ AVRT ❑ Sinus node re-entry ❑ Focal AT Persisting atrial tachycardia with transient high-grade AV block ❑ Atrial flutter ❑ Atrial tachycardia

If adenosine fails, administer ONE of the following: ❑ IV verapamil 5 mg IV every 3-5 min, maximum 15 mg (Class I, level of evidence A) ❑ IV diltiazem (Class I, level of evidence A) ❑ 0.25 mg/kg over 2 minutes ❑ Additional 0.35 mg/kg over 2 minutes ❑ Maintenance infusion of 5-15 mg/hour ❑ IV beta blocker (Class IIb, level of evidence C) ♦ Metoprolol ❑ 5 mg over 2 minutes ❑ Up to 3 doses within 15 minutes ♦ Esmolol ❑ 250-500 μg/kg over 1 minute ❑ Maintenance with 50-200 μg/kg over 4 minutes (if needed) ♦ Propranolol ❑ 0.15 mg/kg over 2 minutes ❑ Monitor ECG continuously

Terminated arrhythmia

Persistent arrhythmia

No further therapy is required if: ❑ Patient is stable ❑ LV function is normal ❑ Normal sinus rhythm on ECG

❑ Administer AV-nodal-blocking agent AND one of the following ❑ IV ibutilide‡ ❑ 1 mg over 10 minutes (if ≥ 60 kg) ❑ 0.01 mg/kg over 10 minutes (if <60 kg) ❑ Repeat once after 10 minutes if needed ❑ IV procainamide ❑ 30 mg/min infusion, maximum 17 mg/kg ❑ Maintenance 2-4 mg/min ❑ IV flecainide 2mg/kg over 10 min OR ❑ DC cardioversion

† Adenosine should be used cautiously in patients with severe coronary artery disease and may produce AF.
‡ Ibutilide is especially indicated for patients with atrial flutter but should not be used in patients with ejection fraction less than 30% as it increases risk of polymorphic VT.

Type of Arrhythmia	EKG (lead II)†	Clues
Supraventricular tachycardia		Any tachyarrhythmia that is initiated and maintained in atrial tissue or atrioventricular junctional tissue.
Sinus tachycardia		Rhythm with heart rate > 100 bpm, originating in SA node due to its increased automaticity.
Sinus node re-entry tachycardia		Rare paroxysmal tachycardia arising due to re-entry circuits with in SA node.
Atrial fibrillation		Supraventricular tachycardia with irregularly irregular rhythm and absent P waves on EKG.
Atrial flutter		Cardiac rhythm characterized by an atrial rate ranging from 240 to 400 beats per minute and regular continuous wave-form.
AVNRT		Most common form of PSVT with a heart rate of 140-250 bpm, re-entrant circuit involves two separate anatomical pathways (slow and fast) loacted in perinodal tissue.
AVRT		Re-entrant tachycardia occurring due to an accessory pathway in addition to AV node, accessory pathway is essential for the initiation and the maintenance of tachycardia.
Focal atrial tachycardia		Focal atria tachycardia refers to a rhythm originating from a single site either in the left or right atrium with an atrial rate of 100-250 bpm.
Nonparoxysmal junctional tachycardia		Benign tachycardia occurring due to increased automaticity arising from a high junctional focus.
Multifocal atrial tachycardia		Irregular tachycardia characterized by 3 different P wave morphologies on EKG.

† EKG strips are a courtesy from ECGpedia.

Do's

• Refer patients with narrow complex tachycardia with any of the following to a cardiac arrhythmia specialist:

• Drug resistance
• Intolerance to drugs
• Refusal of drug therapy
• Severe symptoms such as syncope and dyspnea
• Wolff-Parkinson-White syndrome

• Consider trying different types of anti-arrhythmic agents in case the SVT is refractory; however, closely monitor the blood pressure and heart rate.

• Consider invasive electrophysiological investigation in presence of pre-excitation and severe disabling symptoms.

• Monitor the 12 lead ECG during the administration ofadenosine or carotid massage.

• Make sure the equipment for resuscitation is available during the administration of adenosine in case of the occurrence of any complication, such as ventricular fibrillation or bronchospasm.

• Consider esophageal pill electrodes in cases of invisible P waves.
• Administer higher doses of adenosine in patients taking theophylline.
• Perform the following tests when indicated:

• Echocardiography in case of sustained SVT to rule out structural heart disease
• 24 hour holter monitor in case of frequent but transient tachycardia
• Loop recorder in patients with less frequent arrhythmias
• Trans-esophageal atrial recordings if other investigations have failed to document an arrhythmia

Don'ts

• Do not perform esophageal stimulation if an invasive electrophysiological investigation is planned.
• Do not initiate treatment with anti-arrhythmic agents in a patient with undocumented arrhythmia.
• Do not administer adenosine in patients with severe bronchial asthma or heart transplant recipients.

References

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