ECG IN VENTRICULAR PRE-EXCITATIONECG in Other Conditions

VENTRICULAR PRE-EXCITATION SYNDROME

Definition = the activation of a ventricular territory (preexcited territory) before the arrival of the impulse through the normal AV conduction system due to the existence of an accessory pathway that delivers the impulse beforetime in that aria.

ACCESSORY PATHWAYS Kent bundle (Kent fascicle) =

connects the atria to the basis of the ventricle (RA – RV or LA – LV).

James bundle = connects the atria to the inferior part of AV node or to the His bundle

Mahaim fibers = connect the inferior part of AV node/His bundle to a small part of the septum

WPW (WOLFF-PARKINSON-WHITE) SYNDROME

The pre-excitation syndrome determined by the existence of a Kent bundle.

The impulse arrives earlier from atria to ventricle via Kent bundle than via normal pathway; upon arrival in the ventricular myocardium the early depolarization stimulus is moving slower, because is transmitted through non-specific tissue.

On ECG these aspects determine: short PQ interval. delta wave (Δ): a ‚slow’ wave situated at the beginning of the QRS complex. Wide QRS complex ( due to the presence of delta wave) secondary ST-T changes may appear (especially in cases with

large Δ waves) There are 2 types of WPW syndrome

TYPE A WPW SYNDROME left Kent bundle (from LA to LV) = the pre-

excited territory is situated in LV. rare.

ECG findings: Positive Δ wave and tall R in V1, V2, L3,

aVF Negative Δ wave and predominant

negative complex in left leads QRS axis is right deviated Secondary ST-T changes.

TYPE B WPW SYNDROME right Kent bundle (from RA to RV) = the pre-

excited area is situated in right ventricle. the most frequent form of WPW syndrome.

ECG findings: Negative Δ wave and predominant negative

complex in V1, V2, D3, aVF Positive Δ wave and tall R wave in left leads QRS axis is left deviated. ST-T - secondary changes.

LGL (LOWN- GANONG- LEVINE) SYNDROME

The James fibers are shortcutting the AV node=> the impulse arrives earlier in His system.

The impulse travels through the His system so the QRS complex is narrow(no delta waves).

On ECG: short PR interval (<0.12’’)

MAHAIM FIBERS Normal PR interval (the impulse from the atria

travels through the AV node). A small delta wave at the beginning of the

ventricular complex (a portion of the septum is pre-excited).

Usually there are no ST-T changes

THE RISKS OF THE ACCESSORY PATHWAYS

The developing of a tachycardia by a reentry mechanism.

In an atrial tachyarrhythmia (atrial fibrillation or atrial flatter), if AV node is by-passed, the ventricles will develop a ventricular tachyarrhythmia.

ECG IN OTHER CONDITIONS

DIGITALIS EFFECTS ON ECG digitalis acts by inhibiting Na-K pump and by

enhancing vagal tone It is used in atrial fibrillation and cardiac failure

(NYHA III and IV) Inhibits the SA node leading to sinus bradycardia

and the AV node leading to AV blocks Increases the excitability of the idioventricular

centers leading to frequent multifocal ventricular premature beats which can lead to ventricular tachyarrhythmia

‚coved’ ST segment depression flattened T wave

ECG IN HYPERKALEMIA

Prolonged depolarization Long PQ interval >0.20 secondsWide QRS complex > 0.12 seconds.

Shorter repolarizationShort QT intervalTall T wave with shorter base

ECG IN HYPOKALEMIA

Prolonged repolarization Longer QT interval and a higher risk for

development of torsade de pointes T wave has a longer duration, becomes bifid, with

the first part rather flat, and the second part taller (the second part of the T wave has been identified for a long time as a abnormal ‚u’ wave).

Hypercalcemia

Shorter QT interval due to a shorter ST segment In very severe cases Osborn waves appear (also

called ‚J’ waves) = waves situated at the junction of QRS complex with ST segment. This determines a wider ventricular complex.

Hypocalcemia Prolonged QT interval due to a longer ST segment