How to count ventricular rate in an electrocardiogram (ECG) with ventricular bigeminy?

How to Count Ventricular Rate in ECG with Ventricular Bigeminy

When counting ventricular rate in the presence of ventricular bigeminy, count only the conducted sinus beats (the normal QRS complexes), not the premature ventricular complexes (PVCs), as the PVCs often do not generate effective cardiac output and can create an apical-radial pulse deficit.

Understanding the Clinical Context

Ventricular bigeminy creates a unique challenge for heart rate assessment because:

• Patients with bigeminy present with effective bradycardia and an apical-radial pulse deficit 1
• The premature beats may not generate sufficient stroke volume to create palpable peripheral pulses 1
• Effective bradycardia from PVCs can result in inaccurate estimation of the heart rate 1
• This leads to relative hypertension with a wide pulse pressure 1

Practical Method for Rate Calculation

Step 1: Identify the Pattern

• Ventricular bigeminy consists of alternating normal sinus beats and PVCs in a 1:1 pattern 2
• The PVCs have relatively fixed coupling intervals in most cases 3
• Look for wide, bizarre QRS complexes (the PVCs) alternating with normal QRS morphology 1

Step 2: Count Only Sinus Beats

• Measure the interval between consecutive sinus beats (R-R interval of normal complexes)
• Ignore the PVCs when calculating the underlying sinus rate
• The sinus rate represents the true atrial rate and the effective ventricular rate for perfusion

Step 3: Calculate the Rate

• Use the standard 300/150/100/75/60/50 method or the 1500 method for the R-R interval between sinus beats
• Alternatively, count the number of sinus beats in a 6-second strip and multiply by 10

Important Clinical Considerations

Common Pitfalls to Avoid

• Do not count both sinus beats and PVCs together, as this will give you double the actual effective heart rate 1
• Do not assume the rhythm is simple sinus bradycardia without carefully examining for hidden PVCs 4
• Be aware that ≥2 PVCs per 10-second tracing is considered abnormal and warrants further evaluation 1

When Bigeminy Indicates Pathology

The presence of frequent ventricular bigeminy (>5% of total ventricular arrhythmias) may indicate:

• Long QT syndrome with corrected QT >0.5 seconds 3
• Underlying structural heart disease requiring echocardiographic evaluation 1
• Andersen-Tawil syndrome if there are ≥42 episodes of bigeminy or ≥36.1% of PVCs in bigeminy pattern 2
• Myocardial ischemia, particularly in the setting of acute illness 5

Documentation Approach

When reporting the rate:

• State both the underlying sinus rate and note the presence of ventricular bigeminy
• Example: "Sinus rhythm at 60 bpm with ventricular bigeminy" rather than "heart rate 120 bpm"
• This accurately reflects the effective cardiac output and guides clinical management 1