Short PQ syndrome on ECG

Basic principles of ECG diagnostics

To detect atrioventricular conduction anomalies, which include shortening of the P-Q interval, standard 12-lead ECG is the basic and strictly mandatory method. This study is indicated for all patients with existing or suspected conduction disorders and bradyarrhythmias.

Recording a resting electrocardiogram allows to:

• Document the rate and character of the heart rhythm.
• Detailed assessment of atrioventricular (AV) and intraventricular conduction.
• Analyze myocardial repolarization processes.
• Perform risk stratification and differentiate pre-excitation from other pathologies with similar symptoms (e.g., Brugada syndrome or channelopathies).

Resting ECG should always be performed before stress testing, Holter monitoring, or an electrophysiological study (EPS). If the conduction disorder is intermittent (transient), prolonged monitoring and specialized provocative tests are used to verify the diagnosis. It should be remembered that taking certain medications and electrolyte disturbances can distort the ECG picture (cause QRS prolongation or repolarization abnormalities).

Lown-Ganong-Levine (LGL) syndrome

LGL syndrome is a specific form of conduction anomaly that has clear electrocardiographic boundaries.

The main and only criterion of this syndrome is shortening of the P-Q interval (its duration is less than 0.12 s). At the same time, the ventricular QRS complex remains completely unchanged (normal). The absence of deformation and widening of the QRS complex is a key sign that distinguishes LGL syndrome from other variants of premature ventricular excitation.

Wolff-Parkinson-White (WPW) syndrome

The diagnosis of WPW syndrome is established exclusively based on ECG data. The mechanism of its development is associated with the passage of an electrical impulse via an accessory pathway — the Kent bundle. Since the impulse bypasses the physiological delay in the AV node, shortening of the P-Q interval occurs (less than 0.12 s).

In addition to a short P-Q, WPW syndrome is characterized by a triad of specific signs:

1. Changes in the QRS complex: it becomes widened.
2. Presence of a $\Delta$ wave (delta wave): it is registered on the initial upslope of the QRS complex. The mechanism of its appearance is due to premature depolarization of the area of the ventricular myocardium to which the impulse approached via the Kent bundle. The remaining part of the ventricular complex is formed by a normal impulse that passed through the standard pathway via the AV junction.
3. Secondary repolarization changes: discordance is observed — ST-segment displacement and T-wave polarity changes occur in the direction opposite to the main wave of the deformed QRS complex.

Topical diagnostics (determining the localization of the accessory pathway) is carried out by typing using lead $V_1$. In type A, the delta wave in this lead is positive, while in type B, it is negative.

Prognosis and associated studies

The clinical prognosis in ventricular pre-excitation syndromes is considered unfavorable. The presence of additional conduction pathways creates ideal conditions for the occurrence of paroxysmal arrhythmias. The development of atrial fibrillation against the background of pre-excitation poses a particular danger to the patient's life.

For a comprehensive assessment of structural heart disease that may accompany ventricular tachyarrhythmias, echocardiography (EchoCG) is most often used. Compared to MRI and CT, this method is characterized by high availability and lower cost. EchoCG allows accurate assessment of left ventricular systolic function, regional wall motion, and detection of valvular or myocardial diseases associated with the risk of sudden cardiac death.

What else to study on this topic

• Electrocardiographic criteria for Brugada syndrome
• Hereditary channelopathies: long and short QT syndromes
• Principles of topical diagnostics of the Kent bundle in WPW
• The role of EchoCG in detecting structural heart pathologies in arrhythmias
• Indications for ambulatory ECG monitoring in bradyarrhythmias

Other topics in the "Additional Topics" section

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