Cardiac channelopathies: diagnosis and contemporary management

Introduction The inherited arrhythmia (IA) syndromes are a group of disorders characterised by an increased risk of sudden cardiac death (SCD), abnormal cardiac electrical function and typically, a structurally normal heart.1 They share an underlying genetic aetiology where disease-causing genetic variants may lead to absence or dysfunction of proteins involved in generation and propagation of the cardiac action potential. Table 1 Modified Schwartz score for diagnosis of LQTS≥3.5 points=high probability of LQTS; 1.5–3 points=intermediate probability of LQTS; ≤1 point=low probability of LQTS Electrocardiographic findings* Points A QTc ≥480 ms 3 QTc 460–479 ms 2 QTc 450–459 (in men) 1 B QTc fourth minute of recovery from exercise stress ≥480 ms 1 C Torsades de pointes† 2 D T wave alternans 1 E Notched T wave in three leads 1 F Low heart rate for age‡ 0.5 Clinical history A Syncope with stress† 2 Syncope without stress† 1 B Congenital deafness 0.5 Family history A Family member with definite LQTS§ 1 B Unexplained sudden cardiac death below age 30 among immediate family members§ 0.5 *In the absence of disorders known to affect the electrocardiographic features. †Mutually exclusive. ‡Resting heart rate below second percentile for age. §The same family member cannot be counted in A and B. LQTS, Long QT Syndrome. ECG changes in patients with BrS can be dynamic or concealed and therefore, in suspected cases, provocative testing with sodium-channel blocking drugs can be considered (class IIa recommendation).8 Ajmaline, commonly used in the UK, is the most sensitive.14 Precipitation of a type 1 Brugada ECG pattern in ≥1 lead (including high RV leads) after a dose up to 1 mg/kg (max 100 mg) constitutes a positive result.1 Low rates of sudden cardiac arrest in patients diagnosed following a positive sodium channel blocker provocation alone and the possibility of false-positive results have led to concerns over potential inaccuracy. Table 2 Diagnostic scoring system for Brugada syndrome Points ECG (12-lead/ambulatory) Spontaneous type 1 Brugada ECG pattern* 3.5 Fever-induced type 1 Brugada ECG pattern* 3 Type 2 or 3 Brugada ECG pattern that converts with provocative drug challenge* 2 Clinical history Unexplained cardiac arrest or documented VF/PMVT 3 Nocturnal agonal respirations 2 Suspected arrhythmic syncope 2 Syncope of unclear mechanism/unclear aetiology 1 Atrial flutter/fibrillation in patients