07. Complex Supraventricular Arrhythmias and Differential Diagnosis
Supraventricular tachycardias (SVT) in adults require systematic analysis of the relation between the QRS complex and the retrograde P wave ($RP$ interval).
1. Electrophysiological Classification by $RP$ Interval
NARROW COMPLEX TACHYCARDIA │ ┌─────────────────────┴─────────────────────┐ SHORT RP TACHYCARDIA LONG RP TACHYCARDIA (RP < PR) (RP > PR) │ │ ┌─────────────┴─────────────┐ ┌─────────────┴─────────────┐ Typical AVNRT AVRT Atypical AVNRT PJRT (Pseudo-r' in V1, (RP > 70 ms, (Fast-Slow) (Inverted P II, III) RP < 70 ms) Retrograde P) │ │ Focal Atrial Tachycardia Sinus Tachycardia
2. Detailed Differentiation Matrix
| Tachycardia Entity | Mechanism & Circuit | 12-Lead Electrocardiographic Signatures | Intracardiac EPS & Diagnostic Hallmarks | Definitive Curative Therapy |
|---|---|---|---|---|
| Typical AVNRT (Slow-Fast) | Dual AV nodal pathways; antegrade down slow pathway, retrograde up fast. | Pseudo-$r'$ in lead $V_1$ and pseudo-$S$ in inferior leads (retrograde P buried in terminal QRS, $RP < 70\text{ ms}$). | VA interval $\le 60\text{ ms}$ on His Bundle electrogram; concentric atrial activation. | RF Catheter Ablation of the Slow Pathway ($>98\%$ success, $<0.5\%$ heart block). |
| Orthodromic AVRT | Antegrade down AV node, retrograde up accessory pathway. | Discrete retrograde P wave visible in ST segment or T wave ($RP > 70\text{ ms}$); electrical alternans during rapid rates. | VA interval $>100\text{ ms}$; eccentric atrial activation if free-wall pathway. | RF Catheter Ablation of the Accessory Pathway. |
| Atypical AVNRT (Fast-Slow) | Antegrade down fast pathway, retrograde up slow. | Long RP interval ($RP > PR$), inverted P wave preceding next QRS. | VA interval prolonged; concentric activation. | Slow pathway ablation. |
| Permanent Junctional Reciprocating Tachycardia (PJRT) | Decrementally conducting posteroseptal accessory pathway. | Incessant narrow-complex tachycardia; deeply inverted P waves in II, III, aVF with long RP interval. | High risk of Tachycardia-Induced Cardiomyopathy. | Catheter ablation of posteroseptal pathway. |
| Focal Atrial Tachycardia (FAT) | Automatic or microreentrant atrial focus. | P-wave morphology distinct from sinus P; long RP interval; warm-up and cool-down periods. | Independent of AV nodal conduction; adenosine produces AV block without terminating tachycardia. | 3D activation mapping and focal RF ablation. |
3. Emergency Management & Pharmacotherapy
- Vagal Maneuvers: Modified Valsalva Maneuver (strain at $40\text{ mmHg}$ for $15\text{ s}$, then immediate supine repositioning with passive leg raise to $45^\circ$ for $15\text{ s}$) increases cardioversion success from $17\%$ to $>43\%$.
- IV Adenosine Protocol: $6\text{ mg}$ rapid push via large antecubital vein $\to$ if unsuccessful within $2\text{ minutes}$, give $12\text{ mg}$ rapid push.