What is intraventricular conduction delay (IVCD) on an electrocardiogram (ECG)?

Intraventricular Conduction Delay on ECG

Intraventricular conduction delay (IVCD) on ECG is characterized by a QRS duration ≥110 ms with a morphology that doesn't meet specific criteria for right or left bundle branch blocks, representing abnormal electrical propagation through the ventricular conduction system. 1

Definition and Classification

Intraventricular conduction delays can be categorized into several types:

• Nonspecific IVCD: QRS duration ≥110 ms with morphology that doesn't meet criteria for specific bundle branch blocks

  • Profound nonspecific IVCD: QRS ≥140 ms regardless of morphology 1

• Bundle Branch Blocks:

  • Complete Right Bundle Branch Block (RBBB): QRS ≥120 ms, rsr', rsR', rSR', or qR pattern in leads V1 or V2, and S wave duration greater than R wave or >40 ms in leads I and V6 1
  • Complete Left Bundle Branch Block (LBBB): QRS ≥120 ms, broad notched/slurred R wave in leads I, aVL, V5, and V6, absent Q waves in leads I, V5, and V6, and R peak time >60 ms in leads V5 and V6 1

• Fascicular Blocks:

  • Left Anterior Fascicular Block (LAFB): QRS <120 ms, frontal plane axis between -45° and -90°, qR pattern in lead aVL, R-peak time in lead aVL of ≥45 ms, and rS pattern in leads II, III, and aVF 1
  • Left Posterior Fascicular Block (LPFB): QRS <120 ms, frontal plane axis between 90° and 180°, rS pattern in leads I and aVL, and qR pattern in leads III and aVF 1

• Bifascicular Blocks: Combinations of the above (e.g., RBBB plus LAFB) 2

Clinical Significance

IVCDs have important prognostic implications:

• LBBB and Left Ventricular Conduction Delay (LVCD) are associated with:

  • More than three-fold increased risk of new-onset heart failure 1
  • Increased all-cause mortality (HR 2.3-4.0) and cardiovascular mortality (HR 3.6) 3
  • Worse outcomes in heart failure patients 1

• Nonspecific IVCD is associated with:

  • Higher cardiac mortality in acute coronary syndrome patients (SDH 2.68) 4
  • Poorer prognosis when QRS duration is ≥140 ms 5

• RBBB with left anterior or posterior fascicular block has a particularly ominous prognosis 1

• QRS duration itself is a risk factor - longer duration correlates with increased risk of adverse cardiac events and higher mortality in heart failure patients 1

Diagnostic Evaluation

When IVCD is identified on ECG, the following evaluation is recommended:

1. For newly detected LBBB:

   • Transthoracic echocardiogram to exclude structural heart disease (Class I recommendation) 5, 1

2. For profound nonspecific IVCD (≥140 ms):

   • Echocardiogram to evaluate for myocardial disease 1

3. For symptomatic patients with conduction system disease:

   • Ambulatory electrocardiographic monitoring to establish symptom-rhythm correlation (Class I recommendation) 5
   • Electrophysiologic study (EPS) for symptoms suggestive of intermittent bradycardia (Class IIa recommendation) 5

4. For LBBB with normal echocardiogram but suspected structural heart disease:

   • Advanced imaging (cardiac MRI, CT, or nuclear studies) (Class IIa recommendation) 5, 1

5. For patients with risk factors for coronary artery disease:

   • Stress testing, particularly in those with LBBB 1

Prognostic Implications and Management

The presence of IVCD has important implications for patient management:

• Monitoring: Patients with new-onset LBBB should be monitored closely due to higher risk of adverse outcomes 1

• Cardiac Resynchronization Therapy (CRT): Indicated in heart failure patients with LBBB or significant IVCD 1

• Permanent pacing: May be indicated when IVCD is associated with:

  • Persistent second-degree AV block in the His-Purkinje system with alternating bundle-branch block
  • Third-degree AV block within or below the His-Purkinje system after myocardial infarction
  • Transient advanced second- or third-degree infranodal AV block with bundle-branch block 1

• Development of AV block: The annual incidence of new-onset LBBB is approximately 2.5% in heart failure patients, and is associated with higher risk of adverse outcomes 6

Key Points to Remember

• IVCD represents abnormal electrical propagation through the ventricular conduction system
• QRS morphology and duration provide important diagnostic and prognostic information
• LBBB and nonspecific IVCD with left ventricular conduction delay carry the worst prognosis
• Echocardiography is essential in evaluating patients with newly detected IVCD, particularly LBBB
• Regular ECG monitoring is important as new conduction abnormalities may develop over time