How should I evaluate and manage a patient presenting with tachycardia?

Evaluation and Management of Tachycardia

Immediate Assessment and Stabilization

Determine hemodynamic stability first—if the patient shows acute altered mental status, ischemic chest pain, acute heart failure, hypotension, or shock, proceed directly to synchronized cardioversion without waiting for diagnostic workup. 1

For all patients presenting with tachycardia:

• Attach cardiac monitor, establish IV access, and measure blood pressure immediately 1
• Assess oxygen saturation via pulse oximetry and look for signs of increased work of breathing (tachypnea, retractions) 1, 2
• Provide supplemental oxygen if hypoxemia or respiratory distress is present 1
• Obtain a 12-lead ECG immediately if the patient is stable—this is the single most critical diagnostic tool 1
• Identify reversible causes (infection, anemia, hyperthyroidism, hypovolemia, stimulant use, medications) while initiating treatment 1

Critical Context for Heart Rate Interpretation

• Heart rates <150 bpm rarely cause hemodynamic instability unless ventricular function is already impaired 1, 2
• Sinus tachycardia requires treatment of the underlying cause, not the heart rate itself 1, 2
• The maximum predicted sinus rate is approximately 220 minus age in years 2
• When cardiac function is poor, cardiac output may depend on the rapid rate—"normalizing" the heart rate can be detrimental 1, 2

Management Algorithm Based on Stability

Unstable Patients (Immediate Action Required)

Perform immediate synchronized cardioversion for any tachycardia causing hemodynamic compromise. 1, 3

• Sedate the patient if conscious and time permits 1
• For unstable wide-complex tachycardia, presume ventricular tachycardia and cardiovert immediately 1
• Consider precordial thump only for witnessed, monitored unstable VT if defibrillator not immediately available 1
• Do not delay cardioversion to obtain a 12-lead ECG 1, 3

Stable Patients (Systematic Approach)

Step 1: Determine Rhythm Regularity

Assess whether the ventricular rhythm is regular or irregular on the 12-lead ECG. 1

Irregular narrow-complex tachycardia:

• Most commonly atrial fibrillation, multifocal atrial tachycardia, or atrial flutter with variable block 4, 1
• Use beta-blockers as first-line for ventricular rate control 1
• Non-dihydropyridine calcium channel blockers (diltiazem) are acceptable alternatives 1

Regular narrow-complex tachycardia:

• Consider AVNRT, orthodromic AVRT, atrial flutter with fixed block, or atrial tachycardia 1
• Proceed to Step 2

Step 2: Assess QRS Width

Measure QRS duration: <120 ms = narrow-complex; ≥120 ms = wide-complex. 1

Regular Narrow-Complex Tachycardia Management

Administer adenosine 6 mg rapid IV push followed immediately by saline flush; if ineffective after 1-2 minutes, give 12 mg. 1, 5

• Adenosine terminates SVT in approximately 93% of cases 1
• Must be given in a monitored setting due to risk of transient complete heart block 1
• Contraindicated in asthmatic patients (bronchospasm risk) and when pre-excitation is present 1
• Alternative agents: beta-blockers or non-dihydropyridine calcium channel blockers 1

ECG Clues for Narrow-Complex Tachycardia Mechanism

• P-wave buried within or immediately after QRS (pseudo S wave in inferior leads, pseudo R' in V1) indicates typical AVNRT 1
• P-wave in early ST segment (short RP interval) suggests orthodromic AVRT 1
• P-wave later in cycle (long RP interval) suggests atypical AVNRT, PJRT, or atrial tachycardia 1

Wide-Complex Tachycardia Management

Treat all wide-complex tachycardia 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

Pathognomonic Features for VT (Diagnostic)

• AV dissociation (independent P-waves with ventricular rate faster than atrial rate) is diagnostic of VT 1
• Fusion or capture beats are diagnostic of VT 1
• Concordance (all QRS complexes positive or all negative across V1-V6) strongly indicates VT 1

Features Highly Suggestive of VT

• QRS >140 ms with RBBB morphology or >160 ms with LBBB morphology 1
• Prior myocardial infarction with first occurrence of wide-complex tachycardia after the infarct 1
• RS interval >100 ms in any precordial lead 1

Pharmacologic Management of Stable Wide-Complex Tachycardia

Amiodarone 150 mg IV over 10 minutes is recommended for confirmed or presumed VT. 1

• Procainamide 20-50 mg/min is an alternative (avoid in prolonged QT or heart failure) 1
• Adenosine may be used diagnostically for regular monomorphic wide-complex tachycardia of uncertain origin, but can precipitate ventricular fibrillation in patients with coronary artery disease 1
• Never use calcium channel blockers for wide-complex tachycardia unless SVT is definitively proven 1

Special Clinical Scenarios

Pre-excitation (Wolff-Parkinson-White Syndrome)

If the baseline ECG shows pre-excitation (short PR interval, delta wave), refer immediately to cardiac electrophysiology. 1

• Never use AV nodal blocking agents (adenosine, beta-blockers, calcium channel blockers) in pre-excited atrial fibrillation—this can accelerate ventricular response and precipitate ventricular fibrillation 1, 3
• Catheter ablation has a 95% success rate and <5% recurrence rate 6

Inappropriate Sinus Tachycardia

• Defined as persistent sinus rates >100 bpm at rest or average >90 bpm over 24 hours with symptoms, not explained by other conditions 1
• Ivabradine is the most effective pharmacologic agent, reducing resting heart rate from ~98 bpm to ~85 bpm 1
• Beta-blockers or non-dihydropyridine calcium channel blockers are alternatives with lower efficacy 1
• Sinus node ablation carries substantial risks (phrenic nerve injury, need for permanent pacing) and should be reserved for highly symptomatic refractory patients 1

Diagnostic Workup

Essential Investigations

• 12-lead ECG during tachycardia and in sinus rhythm 4, 1
• Thyroid function testing (TSH, free T4) to exclude hyperthyroidism 1
• Complete blood count to rule out anemia 1
• Basic metabolic panel for electrolyte assessment 1
• Transthoracic echocardiography to evaluate structural heart disease 1
• 24-hour Holter or event recorder for paroxysmal episodes 1

Mandatory Referral to Cardiac Electrophysiology

Urgent referral is required for: 1, 3

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

Critical Pitfalls to Avoid

Never delay cardioversion in unstable patients while obtaining a 12-lead ECG. 1, 3

Never use AV nodal blocking agents in pre-excited atrial fibrillation/flutter—this accelerates ventricular response. 1, 3

Never administer adenosine for irregular or polymorphic wide-complex tachycardia. 1, 3

Never normalize heart rate in compensatory tachycardias (fever, sepsis, hypovolemia) where cardiac output depends on the rapid rate. 1, 3

Never combine multiple AV nodal blocking agents with overlapping half-lives—this causes profound bradycardia. 1, 3

Never assume anxiety as the cause without completing full cardiac evaluation—misdiagnosis delays appropriate therapy. 1

Never treat sinus tachycardia with rate-control medications—aggressively search for and treat the underlying cause (infection, anemia, hyperthyroidism, hypovolemia, stimulant use). 1, 2