What is the appropriate workup and initial management for a patient presenting with tachycardia?

Tachycardia Workup

Obtain a 12-lead ECG immediately in all stable patients—it is the single most critical diagnostic tool for identifying the tachycardia mechanism and guiding management. 1

Immediate Assessment and Stabilization

Determine hemodynamic stability first, as this dictates whether you proceed with diagnostic workup or immediate cardioversion. 1, 2

Signs of Instability Requiring Immediate Cardioversion:

• Acute altered mental status 1, 3
• Ischemic chest pain 1, 3
• Acute heart failure 1, 3
• Hypotension or shock 1, 3

Do not delay cardioversion to obtain a 12-lead ECG in unstable patients—proceed directly to synchronized cardioversion after sedation if time permits. 1, 3

Initial Monitoring for All Patients:

• Attach cardiac monitor and obtain vital signs 1, 2
• Establish IV access 1, 2
• Check oxygen saturation via pulse oximetry and assess for increased work of breathing (tachypnea, retractions) 1, 3
• Provide supplemental oxygen if hypoxemia or respiratory distress is present 1, 3

When to Initiate Workup

Heart rate ≥150 bpm indicates a likely primary arrhythmia requiring immediate workup, regardless of symptoms. 2

Below 150 bpm, tachycardia is more likely secondary to physiologic stress (fever, dehydration, pain, anxiety) unless ventricular dysfunction is present. 2

Lower Threshold for Workup:

• Any patient with hemodynamic instability, regardless of rate 2
• Patients with known ventricular dysfunction at rates <150 bpm 2
• Any suspected ventricular tachycardia, even if self-terminated (requires urgent cardiology consultation and echocardiography) 3

ECG Interpretation Algorithm

Step 1: Assess QRS Width

• Narrow-complex (<120 ms): Supraventricular origin 1
• Wide-complex (≥120 ms): Presume ventricular tachycardia until proven otherwise 1, 4

Step 2: Assess Rhythm Regularity

Irregular Narrow-Complex Tachycardia:

• Most commonly atrial fibrillation, multifocal atrial tachycardia, or atrial flutter with variable block 5, 1

Regular Narrow-Complex Tachycardia:

• Consider AVNRT, orthodromic AVRT, atrial flutter with fixed block, or atrial tachycardia 1
• P-wave analysis is critical: 1
  • P-wave buried in or immediately after QRS (pseudo S wave in inferior leads, pseudo R' in V1) = typical AVNRT
  • P-wave in early ST segment (short RP interval) = orthodromic AVRT
  • P-wave later, closer to next QRS (long RP interval) = atypical AVNRT, PJRT, or atrial tachycardia

Wide-Complex Tachycardia:

Treat as ventricular tachycardia unless proven otherwise—administering verapamil or diltiazem for presumed SVT when the rhythm is actually VT can cause hemodynamic collapse or ventricular fibrillation. 1, 4

Step 3: Identify Pathognomonic Features for VT

AV dissociation (independent P-waves with ventricular rate faster than atrial rate) is diagnostic of VT. 5, 1

• Look for irregular cannon A waves in jugular venous pulse and variable intensity of first heart sound on exam 1

Fusion or capture beats are also diagnostic of VT. 1

Concordance (all QRS complexes positive or all negative across V1-V6) strongly suggests VT. 5, 1

Step 4: Apply Additional VT Criteria

• QRS >140 ms with RBBB morphology or >160 ms with LBBB morphology strongly suggests VT 1
• RS interval >100 ms in any precordial lead suggests VT 1
• History of prior myocardial infarction with first occurrence of wide-complex tachycardia after the infarct strongly suggests VT 1, 4

Caveat: These criteria have reduced specificity in patients on class Ia/Ic antiarrhythmics, with hyperkalemia, or severe heart failure. 1

Baseline ECG Review

Pre-excitation pattern (short PR interval, delta wave) on baseline ECG denotes Wolff-Parkinson-White syndrome and warrants immediate electrophysiology referral. 1

Identifying Reversible Causes

Sinus tachycardia requires treatment of the underlying cause, not the heart rate itself. 1, 2

Evaluate and Correct:

• Infection/sepsis 1
• Hypoxemia 1
• Hypovolemia 1
• Anemia 1
• Hyperthyroidism 1
• Electrolyte disturbances (hypokalemia, hypomagnesemia) 1
• Myocardial ischemia 1
• Stimulant or medication exposure 1

Additional Diagnostic Investigations

• Echocardiography to evaluate structural heart disease, especially in recurrent tachycardia 1
• Ambulatory monitoring (Holter or event recorder) for capturing paroxysmal episodes 1, 3
• Thyroid function testing (TSH, free T4) 1
• Complete blood count to rule out anemia 1
• Basic metabolic panel for electrolyte assessment 1

Acute Management of Stable Tachycardias

Regular Narrow-Complex SVT:

• Vagal maneuvers first (Valsalva, carotid sinus massage if no bruit) 1
• Adenosine 6 mg rapid IV push followed by saline flush; if ineffective after 1-2 minutes, give 12 mg 1
• Adenosine terminates SVT in ~93% of cases 1

Regular Wide-Complex Tachycardia (Presumed VT):

• Amiodarone 150 mg IV over 10 minutes, followed by 1 mg/min infusion for first 6 hours 1
• Alternative: Procainamide 20-50 mg/min until arrhythmia suppression, hypotension, QRS widening >50%, or maximum 17 mg/kg (avoid in prolonged QT or heart failure) 1

Irregular Narrow-Complex (AF/AFL):

• Beta-blockers are most effective for ventricular rate control 1
• Non-dihydropyridine calcium-channel blockers (diltiazem) are acceptable alternatives 1

Critical Pitfalls to Avoid

• Never use AV nodal blocking agents (adenosine, beta-blockers, calcium-channel blockers) in pre-excited atrial fibrillation/flutter—this can accelerate ventricular response and precipitate ventricular fibrillation 1, 3
• Never give adenosine for irregular or polymorphic wide-complex tachycardia 1, 3
• Never normalize heart rate in compensatory sinus tachycardia—this may reduce cardiac output when stroke volume is limited 1, 3
• Never combine multiple AV nodal blocking agents with overlapping half-lives—this causes profound bradycardia 1, 3
• Never assume anxiety without completing full cardiac evaluation—misdiagnosis delays appropriate therapy 1

Indications for Urgent Cardiology/Electrophysiology Referral

• Pre-excitation (WPW) on resting ECG with history of paroxysmal palpitations 1, 3
• Wide-complex tachycardia of unknown origin 1, 3
• Recurrent regular paroxysmal palpitations with abrupt onset/termination 1, 3
• Drug-resistant or drug-intolerant tachyarrhythmias 1, 3
• Any suspected ventricular tachycardia, even if self-terminated 3
• Patients desiring definitive, drug-free solution (catheter ablation) 1, 3