Pictures & Pathology

See the substrate for VT: scar tissue, reentry circuits, EP maps, and the devices that treat it.

The Scar: Where VT Lives

Most monomorphic VT in adults originates from scar tissue left behind after a myocardial infarction. The scar is the stage; the reentry circuit is the actor.

Gross pathology of myocardial infarction scar

Gross Pathology: Post-MI Scar

A cross-section of the left ventricle showing a healed myocardial infarction. The pale, thin area is scar tissue (fibrosis) that replaced dead heart muscle. The surrounding dark red tissue is normal, living myocardium.

Plain language: After a heart attack, the dead muscle turns into scar tissue. This scar can't contract and it can't conduct electricity normally. But surviving muscle fibers thread through the scar, creating electrical detours. Those detours become the reentry circuits that cause VT.

The Circuit: How Reentry Works

Reentry Circuit Diagram

A schematic showing how a reentry circuit forms. An electrical impulse encounters a region with two pathways: one conducts normally, the other conducts slowly (through scar). The impulse blocks in one direction in the slow pathway but continues around the circuit, re-entering the slow pathway from the other side.

Plain language: Picture a roundabout with one lane that's always jammed. The electrical signal can't go through the jammed lane head-on, so it goes around the long way. By the time it comes back to the jammed lane from the other direction, traffic has cleared and it slips through. Then it does the same loop again. And again. Each lap is one heartbeat, and the heart races because the laps are fast.

The Map: What the EP Lab Sees

Electroanatomic Voltage Map

A 3D reconstruction of the left ventricle created during an electrophysiology study. The electrophysiologist moves a catheter around the inside of the ventricle, measuring the electrical voltage at each point. Purple/blue areas represent normal, healthy tissue with high voltage. Red areas represent scar tissue with very low voltage. The border zone (yellow/green) is where surviving muscle fibers mix with scar, creating the slow conduction channels that sustain VT.

Plain language: This is like a heat map of the heart's electrical strength. Purple means the tissue is healthy and conducts well. Red means it's scar and barely conducts at all. The yellow and green edges of the scar are where the VT circuit lives, because that's where normal muscle and scar tissue interleave. The electrophysiologist targets this border zone during ablation.

The Procedure: Catheter Ablation

Electrophysiology Study & Ablation

Catheters are threaded through the femoral vein (or artery for left-sided access) into the heart chambers. The mapping catheter records electrical signals at thousands of points to build the voltage map above. Once the critical part of the reentry circuit is identified (the "isthmus" of slow conduction within the scar), the ablation catheter delivers radiofrequency energy to that site, heating the tissue to ~50-60 degrees Celsius and destroying the slow conduction channel.

Plain language: The doctor threads a thin wire from your leg into your heart. The wire has a sensor on the tip that listens to the heart's electricity and builds a map. Once the doctor finds the detour through the scar that causes VT, they heat that spot until the tissue can't conduct anymore. The roundabout is closed. No more laps, no more VT.

The Safety Net: ICD

Implantable Cardioverter-Defibrillator (ICD)

A chest X-ray showing an ICD generator implanted below the left collarbone with a lead (wire) running through the subclavian vein into the right ventricle. The generator contains a battery, a computer that continuously analyzes the heart rhythm, and a capacitor that can deliver a shock within seconds of detecting VT or VF.

Plain language: This is a small computer implanted under the skin near your shoulder. A wire runs from the device into your heart. The device watches every single heartbeat, 24 hours a day. If VT starts, the device can try to pace the heart back to normal rhythm (like tapping someone on the shoulder to get their attention). If that doesn't work, or if the heart goes into VF, it delivers a shock (like a tiny internal defibrillator). The whole process takes seconds, often before the patient even feels symptoms.

The Normal System: What VT Bypasses

Normal Cardiac Conduction System

The electrical pathway of a normal heartbeat: SA node (pacemaker) fires, the impulse spreads through the atria, converges at the AV node (the only electrical bridge between atria and ventricles), then races down the His bundle, splits into right and left bundle branches, and fans out through the Purkinje fibers to activate both ventricles simultaneously in about 80-100ms.

Plain language: Think of the normal conduction system as a highway system. The SA node is the on-ramp. The AV node is a toll booth (slows things down briefly). The His bundle is the highway, the bundle branches are exits right and left, and the Purkinje fibers are local roads that reach every neighborhood at the same time. VT skips the highway entirely. The impulse starts in a neighborhood and has to travel on local roads to reach everywhere else. That's why the QRS is wide: it takes longer when you can't use the highway.