What is the management of the R on T (Premature Ventricular Contraction) phenomenon?

Management of R on T Phenomenon

The R on T phenomenon (closely coupled PVCs falling on the T wave) does not require specific treatment in most clinical settings, as it rarely triggers sustained ventricular arrhythmias in the modern era. 1, 2

Understanding the R on T Phenomenon

The R on T phenomenon occurs when a premature ventricular contraction (PVC) falls on the T wave of the preceding beat, historically thought to be highly arrhythmogenic. However, current evidence demonstrates that R on T PVCs are rare (representing only 1.8% of total PVCs) and do not serve as reliable triggers of severe ventricular tachyarrhythmias in most patients. 2, 3

Key Clinical Context

• R on T PVCs represent few of the initiating beats of paroxysmal ventricular tachycardia and pose minimal risk for sudden death in most settings 3
• In the thrombolytic era for acute MI, R on T-initiated ventricular tachycardias comprise only 3.3% of total VTs and remain rare features 2
• The phenomenon does not reliably predict ventricular fibrillation risk, even in patients with coronary heart disease, unless sustained repetitive beating capacity is already clinically evident 3

Treatment Algorithm

For Acute Myocardial Infarction Setting

When R on T PVCs occur during acute MI with high-risk features (frequent >6/min, multiform, or occurring in short bursts), treat with lidocaine as first-line therapy: 1, 4

• Initial bolus: 1 mg/kg IV (not to exceed 100 mg), given over 5 minutes 1
• Maintenance infusion: 2-4 mg/min (20-50 μg/kg/min) 1, 4
• Continue for 12-24 hours unless other therapeutic indications persist 1
• If lidocaine fails: Use procainamide 1-2 mg/kg IV bolus over 5-minute intervals to cumulative dose of 1,000 mg, followed by maintenance infusion of 20-80 μg/kg/min 1

Critical dosing adjustments to prevent lidocaine toxicity: 1

• Reduce infusion rates by 50% in patients >70 years old
• Reduce doses in congestive heart failure, cardiogenic shock, or hepatic dysfunction
• Calculate based on lean body weight
• Monitor serum levels with prolonged infusions

For Non-Acute MI Settings

No specific treatment is required for isolated R on T PVCs in patients without acute ischemia or structural heart disease. 1, 4

• Beta-blockers are first-line therapy if treatment is needed for symptomatic PVCs or to prevent recurrent arrhythmias 4, 1
• Reassurance is appropriate for asymptomatic patients with structurally normal hearts 4

Special Circumstances Requiring Intervention

Drug-Induced Long QT with R on T

When R on T occurs in the context of QTc prolongation >500 ms (as with torsade de pointes risk): 1

• Immediately discontinue the offending agent (e.g., moxifloxacin, other QT-prolonging drugs) 5
• Correct electrolyte abnormalities, particularly hypokalemia and hypomagnesemia 1
• Monitor continuously until QTc normalizes 1

Pacemaker-Related R on T

In patients with temporary epicardial pacing wires showing undersensing: 6

• Immediately adjust sensing threshold or switch to asynchronous (VOO/DOO) mode if PVCs are frequent
• Consider removing epicardial wires if no longer needed, as undersensing can occur despite appropriate sensing thresholds 6
• Avoid epicardial pacing when frequent PVCs are present 6

Critical Pitfalls to Avoid

Do NOT use prophylactic antiarrhythmic drugs (other than beta-blockers) for R on T PVCs, as they have not proven beneficial and may cause harm. 4 This represents a major shift from historical practice.

Avoid these specific agents in acute coronary syndrome: 4

• Procainamide
• Propafenone
• Ajmaline
• Flecainide

Do not assume R on T automatically requires aggressive suppression - the coupling interval in drug-induced torsade de pointes is actually NOT as short as in idiopathic ventricular fibrillation, despite falling on the T wave 1

When to Escalate Care

Consider immediate cardioversion/defibrillation if: 1

• R on T triggers sustained ventricular tachycardia with hemodynamic instability
• R on T initiates ventricular fibrillation

Refer for electrophysiology study and possible catheter ablation if: 4

• Recurrent symptomatic PVCs despite beta-blocker therapy
• PVC burden >20% causing cardiomyopathy 7
• Recurrent VT/VF despite optimal medical therapy 4

The fundamental principle is that R on T phenomenon itself is a marker rather than a reliable trigger of life-threatening arrhythmias in most contemporary clinical scenarios, and treatment should focus on the underlying substrate (acute ischemia, electrolyte abnormalities, drug effects) rather than the PVC timing alone. 2, 3