What is atrial fibrillation (A fib) with rapid ventricular response (RVR)?

Atrial Fibrillation with Rapid Ventricular Response (AFib with RVR)

Atrial fibrillation with rapid ventricular response is a supraventricular tachyarrhythmia characterized by chaotic atrial electrical activity (fibrillatory waves replacing normal P waves on ECG) combined with an excessively fast ventricular rate, typically exceeding 100-120 beats per minute. 1

ECG Characteristics

On the electrocardiogram, AFib with RVR displays the replacement of consistent P waves with rapid oscillations or fibrillatory waves that vary in amplitude, shape, and timing, accompanied by an irregular and frequently rapid ventricular response. 2

• The atrial cycle length is usually variable and less than 200 milliseconds, corresponding to an atrial rate of ≥300 bpm 2, 1
• RR intervals are absolutely irregular and do not follow a repetitive pattern 2
• QRS complexes are typically narrow unless fixed or rate-related bundle-branch block or an accessory pathway is present 2
• The ventricular rate in RVR frequently exceeds 100-120 bpm, distinguishing it from rate-controlled AFib 1

Pathophysiology of Ventricular Rate

The ventricular response depends on electrophysiological properties of the AV node, autonomic tone (vagal and sympathetic), presence of accessory pathways, and medications affecting AV nodal conduction. 2, 1

• Increased parasympathetic tone and reduced sympathetic tone slow AV nodal conduction, while the opposite accelerates it 2
• Fluctuations in autonomic tone create wide swings in ventricular rate—slow during sleep but rapid during exercise or stress 2
• Extremely rapid rates exceeding 200 bpm strongly suggest the presence of an accessory pathway (such as Wolff-Parkinson-White syndrome) or ventricular tachycardia 2, 1

Critical Warning: Accessory Pathways

In patients with WPW syndrome, AFib with RVR can produce dangerously rapid ventricular rates that may degenerate into ventricular fibrillation and sudden cardiac death. 2

• Drugs that slow AV nodal conduction (digitalis, verapamil, diltiazem) do NOT block accessory pathway conduction and may paradoxically accelerate the ventricular rate 2
• These agents are contraindicated in AFib with preexcitation 2

Hemodynamic Consequences

Acute loss of coordinated atrial mechanical function reduces cardiac output by 5-15%, with more pronounced effects in patients with reduced ventricular compliance. 2, 1

• High ventricular rates limit ventricular filling due to shortened diastolic intervals 2, 1
• Irregularity of the ventricular response further reduces cardiac output—studies show approximately 9-15% reduction compared to regular rhythms at the same mean rate 2
• Persistent ventricular rates above 120-130 bpm may produce ventricular tachycardiomyopathy (tachycardia-induced cardiomyopathy) 2, 1
• Loss of atrial contraction is particularly detrimental in patients with mitral stenosis, hypertension, hypertrophic cardiomyopathy, or restrictive cardiomyopathy 2

Clinical Significance and Complications

AFib with RVR leads to serious complications including heart failure exacerbation, tachycardia-induced cardiomyopathy with prolonged rapid rates, and increased risk of stroke and thromboembolism. 1

• The irregularity of RR intervals causes large variability in the strength of subsequent heartbeats due to force-interval relationships, often resulting in pulse deficit 2
• Reduction of heart rate may restore normal ventricular function and prevent further dilatation and damage to the atria 2

Differential Diagnosis

Several supraventricular arrhythmias may mimic AFib with RVR, including atrial flutter with variable conduction, atrial tachycardias, and rare forms of frequent atrial ectopy. 2, 1

• Most atrial tachycardias and flutter show longer atrial cycle lengths ≥200 ms compared to AFib 2
• A 12-lead ECG of sufficient duration and quality is essential to evaluate atrial activity and confirm the diagnosis 2, 1
• Occasionally, when ventricular rate is very fast, vagal maneuvers, carotid massage, or intravenous adenosine can help unmask atrial activity 2

Common Diagnostic Pitfalls

Regular RR intervals are possible in AFib when AV block or interference by ventricular or junctional tachycardia is present, which may confuse the diagnosis. 2, 1

• AFib with RVR may be misdiagnosed as atrial flutter when atrial activity appears prominent on ECG 1
• In patients with implanted pacemakers, diagnosis may require temporary inhibition of the pacemaker to expose atrial fibrillatory activity 2
• Aberrant conduction occurs commonly during AFib, facilitated by irregularity of ventricular response (Ashman phenomenon)—a long interval followed by a short interval often results in aberrant conduction of the QRS complex closing the short interval 2