The heart is driven by an electrical system that coordinates the contraction of its chambers. This electrical signal begins in the upper chambers and travels rapidly down to the lower chambers, or ventricles, to trigger a synchronized squeeze. Intraventricular Conduction Delay (IVCD) describes a condition where this electrical signal is slowed or partially blocked within the specialized wiring of the ventricles. This delay means the lower chambers do not contract simultaneously or as efficiently as they should, which can potentially affect the heart’s pumping action.
The Mechanism of Electrical Signal Delay
The heart’s electrical impulse starts at the sinoatrial (SA) node, travels to the atrioventricular (AV) node, and then proceeds into the ventricles via a high-speed cable known as the Bundle of His. This main cable quickly divides into the right and left bundle branches, which spread the signal through a network of Purkinje fibers to all parts of the ventricular muscle.
An IVCD occurs when there is damage or interruption along the path of these bundle branches or Purkinje fibers. Instead of the signal traveling swiftly along the dedicated electrical highway, it is forced to detour through the slower muscle tissue of the ventricle.
Because the impulse reaches different parts of the ventricular muscle at varying times, the two ventricles contract out of sync, a condition called electrical dyssynchrony. This lack of coordination can lead to mechanical dyssynchrony, where the heart muscle is not squeezing with optimal force or timing. The result is a less powerful and energy-inefficient heartbeat, which can sometimes reduce the amount of blood the heart pumps with each beat.
Specific Types and Underlying Conditions
IVCD is broadly classified into specific patterns, the most common being the bundle branch blocks, and a category known as non-specific IVCD. A Right Bundle Branch Block (RBBB) means the delay occurs in the wiring leading to the right ventricle. RBBB is frequently found in otherwise healthy individuals and may not carry a significant health risk on its own.
A Left Bundle Branch Block (LBBB) is a delay in the left ventricle’s wiring, and this pattern is often associated with more significant underlying heart disease. LBBB causes a highly uncoordinated contraction of the main pumping chamber, and its presence warrants a thorough cardiac evaluation. Non-specific IVCD (NSIVCD) is diagnosed when the delay does not fit the criteria for a typical LBBB or RBBB, and this pattern is also sometimes linked to a higher risk of adverse cardiac events.
The root causes of IVCD are related to conditions that damage the heart muscle or its conduction system. High blood pressure (hypertension) can thicken the heart muscle, making signal transmission difficult, while coronary artery disease can cause ischemia, or lack of blood flow, which damages the electrical fibers. Other causes include structural heart diseases like cardiomyopathy or heart failure, congenital heart defects present from birth, and the natural degenerative changes or fibrosis that occur with aging. Certain medications and electrolyte imbalances, such as high potassium levels, can also temporarily or permanently impair the electrical signal’s speed.
How Intraventricular Conduction Delay is Detected
Intraventricular Conduction Delay is typically detected incidentally during a routine Electrocardiogram (EKG or ECG). The EKG measures the electrical activity of the heart, representing the ventricular contraction as a spike called the QRS complex. The duration of this complex reflects the time it takes for the electrical signal to spread through the ventricles.
In a healthy heart, the QRS complex is narrow, reflecting rapid and efficient conduction. When an IVCD is present, the electrical signal takes longer to travel, resulting in a QRS complex that is visibly wider than normal, often exceeding 120 milliseconds for a complete block. The specific shape of this widened complex allows a cardiologist to determine the type of delay, such as RBBB or LBBB.
Many individuals with IVCD experience no noticeable symptoms, especially if the underlying cause is benign or the delay is mild. However, if the delay is a sign of significant heart disease or leads to severely uncoordinated pumping, patients may report feeling tired, lightheaded, or dizzy.
Management Strategies and Long Term Outlook
For asymptomatic individuals with an isolated IVCD and no underlying heart disease, the delay itself usually does not require direct intervention. In these cases, the focus is placed on regular monitoring with follow-up EKGs to track any changes in the conduction pattern over time. The primary management strategy involves treating any identified underlying conditions that may have caused the delay.
This includes managing high blood pressure, controlling cholesterol levels, and addressing heart failure or coronary artery disease through medication and lifestyle changes. A new-onset LBBB, in particular, often triggers immediate and more comprehensive testing, such as an echocardiogram, to rule out new structural heart problems.
For patients who have a significant IVCD, such as LBBB, in combination with heart failure and reduced pumping ability, specialized treatment may be considered. Cardiac Resynchronization Therapy (CRT), which involves implanting a specialized pacemaker, can help by delivering electrical impulses to both ventricles simultaneously. This intervention helps restore a coordinated squeeze, which can improve heart function and the long-term outlook for these specific patients.