[Overview ]
Preexcitation syndrome is a clinical syndrome in which a patient has an additional atrioventricular conduction pathway (bypass) in addition to the normal atrioventricular conduction pathway, causing an abnormal electrocardiogram with a tendency to tachycardia. The typical preexcitation syndrome occurs when the excitation travels down the Kent bundle, the variant preexcitation syndrome occurs when the excitation travels down the James bundle, and the bundle-ventricular fiber preexcitation syndrome occurs when the excitation travels down the Mahaim fiber. In addition, some variants may occur, such as intermittent preexcitation, occult preexcitation and latent preexcitation.
[Symptoms and signs]
Pre-excitation syndrome itself does not cause clinical symptoms, but it can be associated with severe arrhythmias or an increased risk of sudden death when coexisting with other diseases. Pre-excitation is often combined with paroxysmal supraventricular tachycardia, mostly in children or young adults, and can occur repeatedly without evidence of organic heart disease; it can also be combined with atrial fibrillation (flutter), and the ventricular rate is often 180-360 beats/min during atrial fibrillation episodes, and syncope or cardiogenic shock can easily occur when the ventricular rate is greater than 200 beats/min.
[ Diagnostic basis ]
1. Typical pre-excitation syndrome.
(1) P-R interval <0.12 sec, normal P wave;
(2) QRS time >0.11 sec;
(3) coarsening and blunting of the beginning part of the QRS wave group, called preexcitation wave or δ wave; (4) secondary ST-T changes.
Clinically, it is further divided into three types.
Type A preexcitation: preexcitation waves and QRS wave groups are upward in all thoracic leads, and their collateral channels are located at the posterior base of the left ventricle.
Type B preexcitation: The main wave of preexcitation and QRS wave group is downward in lead V1 and upward in lead V5 of the left thoracic lead, and the bypass is located in the right ventricular ventricular lateral wall.
Type C preexcitation: the preexcitation wave and QRS wave group V1-V2 leads are upward and V3-V5 leads are downward. It is left ventricular sidewall preexcitation.
2. Variable preexcitation.
LGL-type preexcitation.
(1) P-R interval <= 0.11 sec;
(2)QRS wave group time is normal;
(3) No δ wave
3. Mahaim-type preexcitation: (1) P-R interval <= 0.11 sec; (2) normal QRS wave group time; (3) no δ wave
(1) P-R interval >= 0.12 sec;
(2) QRS integrated wave onset wave has δ wave, but the δ wave is small;
(3) QRS time >= 0.12 seconds, but the widening is slight.
[ Principles of treatment ]
Pre-excitation syndrome itself does not require treatment. However, if combined with rapid supraventricular tachycardia, urgent treatment is often required to terminate the onset of supraventricular tachycardia. If supraventricular tachycardia occurs frequently and cannot be controlled by drugs, esophageal pacing or intracardiac electrophysiological examination is required to determine the location of the bypass and eventually ablation or surgical treatment is performed to cut off the bypass and end the tachycardia.
In cases of recurrent tachycardia caused by abnormal bypass of the cardiac conduction system, radiofrequency ablation therapy should be performed. This method is painless for patients and highly effective, and is currently the best treatment method. If tachycardia cannot be terminated by drug therapy, electric shock resuscitation should be performed.