What are the differential diagnoses and management plan for a 45-year-old man who had three brief episodes in the past week of transient dyspnea, palpitations, a sense of impending cardiac arrest, and generalized fatigue?

Differential Diagnosis and Management Plan

This 45-year-old man is presenting with classic features of paroxysmal supraventricular tachycardia (PSVT), most likely AVNRT or AVRT, though life-threatening ventricular arrhythmias and acute coronary syndrome must be urgently excluded given the sensation of impending cardiac arrest.

Differential Diagnoses (Prioritized by Urgency)

Cardiac Arrhythmias (Most Likely)

Supraventricular Tachycardias:

• AVNRT (AV nodal reentrant tachycardia) or AVRT (AV reentrant tachycardia) - The sudden onset/offset pattern with palpitations, dyspnea, and sense of impending doom strongly suggests paroxysmal SVT 1, 2, 1. These are the most common causes of regular paroxysmal palpitations with sudden onset and termination 1.
• Atrial fibrillation with rapid ventricular response - Can present with irregular palpitations, dyspnea, and fatigue 1, 2.
• Pre-excitation syndromes (WPW) - Must be considered, especially given the potentially serious nature of symptoms 1.

Ventricular Arrhythmias:

• Ventricular tachycardia - The "feeling heart is about to stop" and sense of dying warrant consideration of VT, particularly if there's underlying structural heart disease 3, 4, 5.
• Premature ventricular contractions (PVCs) - Can cause palpitations and pauses but typically less dramatic symptoms 1, 6.

Acute Coronary Syndrome

• Dyspnea, palpitations, and sense of impending doom can represent acute myocardial ischemia or infarction 7, 8.

Channelopathies

• Long QT syndrome, Brugada syndrome, CPVT - Should be considered given the episodic nature and potentially life-threatening presentation 3, 5.

Non-Cardiac Causes

• Panic disorder/anxiety - Can mimic cardiac symptoms but typically has longer prodrome and specific triggers 1, 2.
• Pulmonary embolism - Transient dyspnea and palpitations, though typically more persistent symptoms 9.
• Hyperthyroidism - Causes palpitations and fatigue but symptoms are usually more constant 6.
• Systemic mastocytosis - Rare but can present with recurrent syncope, dyspnea, and palpitations 7.

Immediate Management Plan

1. Emergency Assessment (If Patient Presents During Episode)

Immediate actions:

• Obtain 12-lead ECG during tachycardia before any intervention (unless hemodynamically unstable) 2, 1, 5
• Monitor vital signs: heart rate, blood pressure, oxygen saturation
• Assess for hemodynamic instability: hypotension, altered consciousness, chest pain, acute heart failure 10

If hemodynamically unstable: Immediate synchronized cardioversion 10

If stable with narrow-complex regular tachycardia:

• Attempt vagal maneuvers (Valsalva, carotid massage) 1
• If unsuccessful: Adenosine 6 mg IV rapid push, then 12 mg if needed 10
• Document rhythm response to adenosine (diagnostic and therapeutic) 2

2. Initial Diagnostic Workup (Between Episodes)

Essential investigations:

12-lead ECG in sinus rhythm 2, 5, 11:

• Look for pre-excitation (delta waves suggesting WPW) 2, 1
• QT interval prolongation (>460 ms in males suggests LQTS) 3, 5
• Brugada pattern in right precordial leads 3
• Evidence of prior MI, LVH, or conduction abnormalities 5

Laboratory tests 5:

• Troponin (rule out ACS)
• Thyroid function tests
• Electrolytes (potassium, magnesium, calcium)
• Complete blood count (anemia)
• Renal function

Transthoracic echocardiography 1, 11:

• Assess for structural heart disease (cardiomyopathy, valvular disease, wall motion abnormalities)
• Evaluate LV function
• Rule out HCM, ARVC 3, 5

Ambulatory monitoring 1, 6:

• Event recorder or loop recorder (preferred for episodic symptoms occurring 3x/week) 1
• 24-48 hour Holter if episodes are daily 1
• Patient should activate recorder during symptoms

3. Risk Stratification

HIGH RISK features requiring hospitalization 5, 11:

• Syncope or near-syncope during episodes 2, 1, 5
• Exertional symptoms 5, 11
• Family history of sudden cardiac death <50 years 3, 5
• Known structural heart disease 5, 11
• Abnormal baseline ECG suggesting channelopathy 3, 5

This patient has HIGH RISK features (sense of impending cardiac arrest, multiple episodes) and should be hospitalized for monitoring and evaluation 5, 11.

4. Definitive Management Strategy

If PSVT (AVNRT/AVRT) is confirmed:

Acute episode management:

• Vagal maneuvers first 1
• Adenosine 6-12 mg IV 10
• If refractory: Diltiazem or verapamil IV 10

Long-term management:

• Refer to cardiac electrophysiologist for catheter ablation - This is curative with >95% success rate and should be offered to all patients with documented PSVT, especially those with severe symptoms 1, 2, 1
• Pharmacologic options if ablation declined: beta-blockers, calcium channel blockers, or class IC/III antiarrhythmics 1, 2

If ventricular arrhythmia suspected:

• Urgent cardiology/electrophysiology consultation 3, 4, 5
• Consider ICD if sustained VT or high-risk features 4, 5

If WPW syndrome identified:

• Mandatory referral to electrophysiologist - Risk of sudden death from rapid AF conduction 1
• Avoid AV nodal blocking agents (digoxin, verapamil, diltiazem) 2

5. Family Screening Considerations

Given the potentially serious presentation, obtain detailed family history of 3, 5:

• Sudden cardiac death or unexplained drowning in first-degree relatives
• Known inherited arrhythmia syndromes
• Cardiomyopathies
• If positive family history: Consider genetic testing and family member screening 3

Critical Pitfalls to Avoid

1. Do NOT dismiss symptoms as anxiety without comprehensive cardiac evaluation - The episodic nature and severity warrant full workup 1, 5.

2. Do NOT start class I or III antiarrhythmics empirically without documented arrhythmia due to proarrhythmia risk 1.

3. Do NOT use AV nodal blocking agents if WPW is suspected or confirmed 2, 1.

4. Do NOT rely solely on resting ECG - Most patients with paroxysmal arrhythmias have normal ECGs between episodes 1.

5. Do NOT delay referral to electrophysiology if wide-complex tachycardia of unknown origin is documented 1.

6. Ensure 12-lead ECG is obtained during tachycardia - This is the single most important diagnostic test 2, 1.