Familial cardiac conduction defects belong to the group of inherited arrhythmias and can be classified under the broad heading of ``familial disorders affecting impulse propagation and cardiac conduction''. Patients can be asymptomatic or present with palpitations or occasionally symptoms of hemodynamic disorder, i.e. dizziness, syncope, heart failure, sudden cardiac death. Patients are often well aware of the onset and offset of intermittent tachyarrhythmias. Genetic studies of families with inherited cardiac rhythm disturbances led to the establishment of a molecular basis for arrhythmogenesis disorders. Both autosomal dominant and autosomal recessive transmissions have been described. More recently, mutations in the CSX/NKX2-5 (cardiac-specific homeo box), LMNA A/C (lamin), SNC5A (sodium channel, voltage-gated, type V, alpha subunit), PRKAG2 (protein kinase, AMP-activated, non catalytic, gamma-2) genes have been described, widening the large family of genes causing cardiac conduction defects. Etiology has not been elucidated yet. Most electrocardiographic disturbances are explained by developmental failure, abnormal anatomy, cardiac electrical instability, aberration in autonomic regulation of cardiac conduction or direct substance infiltration of the atrio-ventricular conduction system. The reported frequency can vary from 6 per 100,000,000 in the atrio-ventricular block of second degree to 4.1 per million in the incomplete inter-ventricular block, and 6.3 per million in the atrio-ventricular block of first degree. Diagnosis is suggested by characteristic symptoms. Standard 12-lead electrocardiogram (ECG) and 24-hour ambulatory ECG monitoring confirm the diagnosis. Treatment is based on antiarrhythmic drugs, pharmacological and/or electrical cardioversion in case of tachyarrhythmic episodes and on pacemaker implantation in the case of bradiarrhythmic episodes. Cardiac conduction defects and their pattern of inheritance are listed in table 1.
Last update: May 2003