What is intraventricular conduction delay?

Intraventricular Conduction Delay

Intraventricular conduction delay (IVCD) is an abnormality in the electrical conduction system of the heart characterized by delayed or impaired conduction of electrical impulses through the ventricles, resulting in a widened QRS complex on electrocardiogram (≥110 ms). 1

Definition and Classification

Intraventricular conduction delays can be categorized into several types:

1. Bundle Branch Blocks:

   • Complete Right Bundle Branch Block (RBBB):

     • QRS duration ≥120 ms
     • rsr', rsR', rSR', or rarely a qR pattern in leads V1 or V2
     • S wave of greater duration than R wave or >40 ms in leads I and V6
     • Normal R peak time in leads V5 and V6 but >50 ms in lead V1 1

   • Complete Left Bundle Branch Block (LBBB):

     • QRS duration ≥120 ms
     • Broad notched or slurred R wave in leads I, aVL, V5, and V6
     • Absent Q waves in leads I, V5, and V6
     • R peak time >60 ms in leads V5 and V6
     • ST and T waves usually opposite in direction to QRS 1

2. Fascicular Blocks:

   • Left Anterior Fascicular Block (LAFB):

     • QRS duration <120 ms
     • Frontal plane axis between -45° and -90°
     • qR pattern in lead aVL
     • R-peak time in lead aVL of ≥45 ms
     • rS pattern in leads II, III, and aVF 1

   • Left Posterior Fascicular Block (LPFB):

     • QRS duration <120 ms
     • Frontal plane axis between 90° and 180°
     • rS pattern in leads I and aVL
     • qR pattern in leads III and aVF 1

3. Nonspecific Intraventricular Conduction Delay:

   • QRS duration >110 ms
   • Morphology criteria for RBBB or LBBB are not present 1

Clinical Significance

The clinical significance of IVCD varies depending on:

1. Underlying Cause: IVCD may be associated with:

   • Structural heart disease (cardiomyopathy)
   • Ischemic heart disease
   • Myocardial infarction
   • Congenital heart disease
   • Electrolyte abnormalities
   • Drug effects
   • Degenerative conduction system disease 1

2. QRS Duration: Longer QRS duration is associated with:

   • Increased risk of adverse cardiac events
   • Higher mortality in heart failure patients 2

3. Type of Block: Different types of blocks carry different prognostic implications:

   • LBBB is associated with worse outcomes in heart failure patients
   • RBBB with left anterior or posterior fascicular block has a particularly ominous prognosis 1

Clinical Implications

1. In Heart Failure:

   • Approximately 25% of patients with symptomatic heart failure have IVCD (QRS >120 ms)
   • IVCD leads to dysynchronous ventricular contraction, mechanical inefficiency, and further impairment of left ventricular function 3
   • Patients with HFrEF and wide QRS have worse clinical outcomes regardless of morphology 2

2. After Myocardial Infarction:

   • Development of IVCD after MI reflects extensive myocardial damage
   • Particularly ominous prognosis is associated with LBBB combined with advanced AV block, or RBBB combined with fascicular block 1

3. In Asymptomatic Individuals:

   • Incidental finding of IVCD in individuals without ischemic heart disease may not be an independent risk factor for all-cause mortality 4

Management Considerations

1. Cardiac Resynchronization Therapy (CRT):

   • Indicated in heart failure patients with LBBB or significant IVCD
   • Aims to restore synchronous ventricular contraction
   • Left bundle branch-optimized CRT has shown promising results in improving ventricular electrical synchrony and clinical outcomes in IVCD patients 5

2. 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 MI
     • Transient advanced second- or third-degree infranodal AV block with bundle-branch block 1

3. Monitoring:

   • Patients with new-onset LBBB should be monitored closely as it is associated with higher risk of adverse outcomes
   • Annual incidence of new-onset LBBB is approximately 2.5% in heart failure patients 2

Evaluation

When IVCD is detected, further evaluation may include:

1. Echocardiography: To assess for structural heart disease, particularly in:

   • Complete LBBB
   • Profound non-specific IVCD (≥140 ms)
   • Pathological Q waves in two or more contiguous leads 1

2. Cardiac MRI: May be indicated in cases with normal echocardiogram but high clinical suspicion for underlying myocardial disease 1

3. Stress Testing: In adults ≥30 years with risk factors for coronary artery disease 1

IVCD is not merely an electrocardiographic finding but can reflect significant underlying cardiac pathology and affect prognosis, particularly in patients with heart failure or ischemic heart disease.