[2][3][4] Later, Michel Haïssaguerre's team investigated cardiac fibrillation, the most complex and severe type of arrhythmias, defined as "turbulent, disorganized electrical activity.

A combination of spatiotemporal factors is required to establish reentry, a process occurring at a macroscopic scale rather than at the cellular level, with antiarrhythmic drugs (ion channel blockers) having limited efficacy or even proarrythmic effects in clinic (CAST trial).

Michel Haïssaguerre developed multi-electrode catheters to perform wide area mapping and identify the primary activity at the origin of the fibrillation.

He pioneered the use of catheter ablation to treat atrial fibrillation using the technique of pulmonary vein isolation to prevent this abnormal electrical activity from reaching the atria.

[10] Michel Haïssaguerre's team showed that patients with sudden cardiac death and structurally normal hearts frequently had triggers originating from Purkinje fibers, a physiological tissue representing 2% of myocardial mass.

[11] Despite the effective treatments (implantable defibrillators, ablation) available for lethal ventricular arrhythmias, the major hurdle remains identification of subjects at risk of sudden death.

[13] Further studies have focused on the enigmatic origin of 'sudden unexplained cardiac deaths': those for which no cause is found after a complete autopsy or detailed investigations (surviving patients).