As already discussed in part, this syndrome is characterized by a great variability in the electrocardiographic pattern. The electrocardiogram may be completely abnormal at times, but completely normal at others .

 

This variability has many causes and several explanations. Autonomic changes and body temperature influence the electrocardiogram. So do spontaneous or induced changes in heart rate.

 

An artificial increase in heart rate (by atrial pacing) decreases ST segment elevation, while a decrease in heart rate increases it.

 

These data are again in agreement with the loss of the dome of the action potential at epicardial level as the cause of ST segment elevation. Ito becomes more prominent at slow rates increasing heterogeneity and ST segment elevation.

These data are also in agreement with the clinical observations documenting a bradycardia -dependency and a higher incidence of sudden death during sleep in patients with this syndrome.

 

Normalization of the ST segment during exercise is the most common finding in patients with this syndrome. These are logical findings because both an increase in heart rate and adrenergic stimulation decrease ST segment elevation.

 

"Strength does not come from physical capacity. It comes from an indomitable will"

 

During invasive electrophysiologic investigations sinus node function has been normal in the large majority of the patients. However, isolated patients have manifest sinus node disease and are pacemaker dependent.

As already discussed, about 10% of patients has paroxysmal atrial fibrillation. There exist no detailed studies on the ability to induce this arrhythmia by programmed electrical stimulation.

 

 

All published studies agree on the inducibility of polymorphic ventricular tachycardia by programmed electrical stimulation in symptomatic patients. About 80% of them are inducible by giving 1 or 2 ventricular premature beats during ventricular pacing. In some patients three premature stimuli are required.

 

The induced arrhythmia is sustained in practically all cases, results in hemodynamic collapse and has to be terminated by an external DC shock. It can be criticized that polymorphic ventricular tachycardia or ventricular fibrillation induced by programmed stimulation is a non-specific finding, because these arrhythmias can sometimes be induced in patients with a normal heart. There exist, however, major differences between the two situations:

 

1.- The clinical context, with symptomatic patients with Brugada syndrome having suffered from spontaneous ventricular arrhythmias,

 

2.- The percentage of patients inducible to a sustained polymorphic ventricular arrhythmia in Brugada syndrome (80%) as compared to individuals without the syndrome where a sustained polymorphic ventricular tachycardia or ventricular fibrillation is only exceptionally induced.

 

The same studies coincide in the frequent finding of conduction disturbances in patients with the disease. The H-V interval is prolonged in about the half of the patients. The prolongation is not marked, rarely exceeding the 70 ms, but being clearly abnormal in this population with an average age of 40 years. The H-V prolongation explains the slight prolongation of the P-R interval during sinus rhythm (picture 1).

 

Hemodynamic studies have been systematically normal.