What is Intraventricular Conduction Delay (IVCD) on an Electrocardiogram (ECG)?

Intraventricular Conduction Delay (IVCD) on ECG

Intraventricular conduction delay (IVCD) on ECG is characterized by abnormal, delayed electrical conduction through the ventricles resulting in a widened QRS complex (≥110 ms) that does not meet specific criteria for bundle branch blocks or fascicular blocks. 1

Definition and Classification

IVCD represents impaired conduction of electrical impulses through the ventricular conduction system. It can be classified into several categories:

Types of Intraventricular Conduction Delays:

1. Bundle Branch Blocks

   • Complete Right Bundle Branch Block (RBBB): QRS ≥120 ms with rsr', rsR', or rSR' pattern in V1-V2 and wide S wave in I and V6 1
   • Complete Left Bundle Branch Block (LBBB): QRS ≥120 ms with broad notched/slurred R waves in I, aVL, V5-V6 and absent Q waves in these leads 1

2. Fascicular Blocks

   • Left Anterior Fascicular Block (LAFB): QRS <120 ms, left axis deviation (-45° to -90°), qR in aVL 1
   • Left Posterior Fascicular Block (LPFB): QRS <120 ms, right axis deviation (90° to 180°), rS in I and aVL 1

3. Nonspecific IVCD: QRS ≥110 ms without meeting criteria for RBBB, LBBB, or fascicular blocks 1

ECG Characteristics

• QRS duration ≥110 ms (typically ≥120 ms for complete bundle branch blocks)
• QRS morphology that doesn't meet specific criteria for RBBB or LBBB
• May show features of both RBBB and LBBB (hybrid patterns)
• Profound nonspecific IVCD is defined as QRS ≥140 ms regardless of morphology 2

Clinical Significance

The clinical importance of IVCD varies based on:

1. Underlying cause: IVCD may result from:

   • Structural heart disease
   • Ischemic heart disease
   • Cardiomyopathy
   • Congenital heart defects
   • Electrolyte abnormalities
   • Medication effects
   • Degenerative conduction system disease 1

2. Prognostic implications:

   • LBBB and nonspecific IVCD with left ventricular conduction delay (L-IVCD) are associated with a more than three-fold increased risk of new-onset heart failure 3
   • LBBB is associated with worse outcomes in heart failure patients 1
   • Profound nonspecific IVCD (≥140 ms) warrants further evaluation for myocardial disease 2
   • IVCD without underlying heart disease may not independently increase mortality risk 4

Evaluation Approach

For patients with newly identified IVCD on ECG:

1. For LBBB: Transthoracic echocardiogram is recommended to exclude structural heart disease 2

2. For profound nonspecific IVCD (≥140 ms): Echocardiogram is recommended to evaluate for myocardial disease 2

3. For other types of IVCD: Echocardiography is reasonable if structural heart disease is suspected 2

4. For symptomatic patients with conduction system disease:

   • Ambulatory ECG monitoring is useful when AV block is suspected 2
   • Electrophysiologic study (EPS) is reasonable for symptoms suggestive of intermittent bradycardia 2

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

   • Advanced imaging (cardiac MRI, CT, or nuclear studies) is reasonable 2

Clinical Pitfalls and Caveats

1. Don't confuse nonspecific IVCD with incomplete bundle branch blocks - they have different diagnostic criteria and prognostic implications

2. Recognize that IVCD may be the first sign of underlying heart disease - particularly with LBBB and nonspecific IVCD

3. Consider that IVCD may be transient - due to rate-dependent aberrancy, ischemia, electrolyte abnormalities, or medication effects

4. Be aware that LBBB and L-IVCD carry similar prognostic implications - both are associated with increased all-cause and cardiovascular mortality 5

5. Remember that HV interval prolongation in bifascicular block has high sensitivity (82%) but low specificity (63%) for predicting development of complete trifascicular block 2

IVCD should prompt appropriate evaluation based on the specific type of conduction delay, patient symptoms, and clinical context to identify underlying structural heart disease and assess risk for progression to higher-degree conduction abnormalities.