Should a patient with low voltage QRS (quadrature amplitude modulation of the R and S waves on an electrocardiogram) be referred to cardiology?

Referral to Cardiology for Low Voltage QRS

Patients with low voltage QRS should be referred to cardiology for evaluation as this finding may indicate serious underlying cardiac pathology, particularly cardiac amyloidosis, which has significant implications for morbidity and mortality.

Definition and Significance of Low QRS Voltage

Low QRS voltage is defined as:

• QRS amplitude ≤0.5 mV (5 mm) in all limb leads, or
• QRS amplitude ≤1.0 mV (10 mm) in all precordial leads, or
• Sokolow index ≤1.5 mV 1, 2

Clinical Significance and Underlying Conditions

Low QRS voltage is not a benign finding and may indicate several serious cardiac conditions:

High-Priority Conditions (Require Prompt Cardiology Referral)

• Cardiac Amyloidosis:

  • Present in 34-66% of patients with cardiac amyloidosis 3, 4
  • More common in light chain (AL) amyloidosis (55%) than transthyretin (ATTR) amyloidosis (35%) 3
  • Associated with worse cardiovascular mortality (HR: 1.76-2.64) 3

• Cardiomyopathies:

  • Arrhythmogenic cardiomyopathy (17-40% prevalence) 1
  • Dilated cardiomyopathy (6-7%, up to 36% in certain genetic forms) 1
  • Hypertrophic cardiomyopathy (0.7-11%) - associated with more extensive late gadolinium enhancement on CMR 1

Other Significant Causes

• Pericardial effusion
• End-stage heart failure
• Obesity
• Emphysema
• Peripheral edema of various etiologies 5

Diagnostic Algorithm

1. Confirm true low voltage QRS:

   • Verify QRS amplitude ≤0.5 mV in all limb leads or ≤1.0 mV in all precordial leads
   • Calculate Sokolow index (SV1 + RV5/V6)

2. Assess for immediate red flags:

   • Presence of syncope or pre-syncope
   • Heart failure symptoms
   • Ventricular arrhythmias
   • Family history of sudden cardiac death

3. Evaluate for extracardiac causes:

   • Peripheral edema
   • Severe obesity
   • Emphysema/COPD

4. Refer to cardiology when:

   • Low QRS voltage is confirmed without obvious extracardiac cause
   • Any red flag symptoms are present
   • Patient is an athlete with low QRS voltage (2.2-4% prevalence in elite athletes) 1
   • Patient has known or suspected heart disease

Recommended Cardiology Evaluation

The cardiology evaluation should include:

1. Echocardiography: To assess for:

   • Increased ventricular wall thickness with granular sparkling appearance (amyloidosis)
   • Pericardial effusion
   • Ventricular dysfunction
   • Cardiomyopathy features

2. Cardiac MRI: Particularly valuable for:

   • Late gadolinium enhancement patterns
   • Tissue characterization
   • Identification of infiltrative diseases

3. Laboratory testing:

   • NT-proBNP/BNP levels
   • Troponin
   • Serum and urine protein electrophoresis (for AL amyloidosis)
   • Genetic testing when appropriate

Prognostic Implications

Low QRS voltage has significant prognostic implications:

• Independent predictor of cardiovascular death in both AL and ATTR cardiac amyloidosis 3
• Associated with higher risk of sudden death, sustained ventricular arrhythmias, and appropriate ICD discharge in cardiomyopathies 1
• Provides incremental prognostic value beyond established staging systems in ATTR amyloidosis 3

Important Caveats

• Low QRS voltage is relatively rare in healthy individuals (0.3%) and recreational athletes (0.5%) 1
• The finding may be a late manifestation in cardiac amyloidosis, so absence does not rule out early disease 4
• Peripheral edema can cause reversible low QRS voltage and also affect other ECG parameters 5
• Different criteria for defining low voltage yield different prevalence rates, with Sokolow index ≤1.5 mV having the highest sensitivity for detecting clinically significant disease 4

Low QRS voltage should never be dismissed as a benign finding without appropriate cardiac evaluation, as it may represent the first indication of a serious cardiac condition with implications for morbidity and mortality.