Diagnosis of BrS is made in the presence of a type 1 pattern on the ECG (coved-type ST-segment elevation of ≥2 mm in one or more of the right precordial leads, V1 and/or V2, in the second, third or fourth intercostal space), spontaneously or following provocation with a sodium channel blocker such as flecainide or ajmaline.8–10

To avoid overdiagnosis, when a type 1 pattern has been documented on the ECG only after pharmacological provocation, at least one of the following criteria should also be fulfilled for a diagnosis of BrS: VF or polymorphic VT; syncope of probable arrhythmic cause; family history of SD before the age of 45 years with negative autopsy; type 1 pattern in relatives; nocturnal agonal respiration; or inducibility of VT/VF.8 Table S1 in Supplement 6 presents a diagnostic score for BrS.8

BrS is associated with genetic variants in multiple genes, most of which code for sodium channels (SCN5A in 11-28% of probands, SCN10A in 5-17%) or calcium channels (CACNA1C in 7% and CACNB2b in 5%).8

Genetic testing is not necessary for the diagnosis, but can be useful in cases of doubtful phenotypes and in those with established BrS (class IIb3 or IIa2 recommendation), particularly to facilitate familial genetic screening (class IIb3) (Table 1).

Diagnosis of ERS is based on a pattern of early repolarization in the inferior and/or lateral leads and a history of aborted SD, documented VF or polymorphic VT.8 ER is recognized if (1) there is an end-QRS notch (J wave) or slur on the downslope of a prominent R wave with and without ST-segment elevation; (2) the peak of the notch or J wave (Jp) ≥0.1 mV in ≥2 contiguous leads of the 12-lead ECG, excluding leads V1-V3; and (3) QRS duration (measured in leads in which a notch or slur is absent) of <120 ms.11 Table S2 in Supplement 6 presents a diagnostic score for ERS.8

ERS has so far been associated with genetic variants in seven genes, mainly coding for calcium channels (CACNA1C, CACNB2b and CACNA2D1), but their etiological role is questionable8 and so genetic testing is not recommended3 (Table 1).

The diagnosis of long QT syndrome (LQTS) is based on measurement of the QT interval after excluding secondary causes of QT prolongation such as drugs or electrolyte imbalances.10 To help with diagnosis, a score has been created12 that as well as corrected QT interval (QTc) also considers other electrocardiographic abnormalities, symptoms, and family history (Table S3, Supplement 6). The diagnosis is now established with either QTc ≥480 ms in repeated ECGs (class I) or LQTS risk score >3 (class I), or in the presence of a confirmed pathogenic LQTS mutation, irrespective of the QT duration (class I); it should be considered in the presence of QTc ≥460 ms in repeated 12-lead ECGs in patients with unexplained syncope.9

LQTS is associated with documented genetic variants in at least 15 genes.13 Genetic testing identifies pathogenic variants in around 75% of cases, and three genes are responsible for about 90% of positive tests: KCNQ1, KCNH2 and SCN5A (associated with types 1, 2 and 3 LQTS, respectively.9 Genetic testing is of particular value in these cases, since the three genotypes are associated with different degrees of SD risk, especially in association with gender and QTc duration (the risk is highest in women with type 2 LQTS and in men with type 3 LQTS and QTc >500 ms6,14), and since the triggers for arrhythmic events also differ (physical exertion, particularly swimming, in type 1; sudden loud noises in type 2; and rest or sleep in type 3).6,15 Around 20-25% of patients with genetically confirmed LQTS have a normal QTc.10,16

Molecular study may be aimed at a specific gene or may be guided by the ECG, syncope triggers or the characteristics of associated syndromes. In patients with congenital deafness, cardiac malformations, cognitive deficit, autism spectrum disorder and/or dysmorphisms, diagnostic hypotheses should include Jervell and Lange-Nielson, Timothy, or Andersen-Tawil syndromes. Alternatively the use of gene panels that screen multiple genes associated with LQTS can help diagnose rarer forms of the disease.17

Jervell and Lange-Nielson syndrome is an autosomal recessive disorder, more rarely compound heterozygous, involving the genes KCNQ1 or KCNE1, in which long QTc, usually >500 ms, is associated with congenital profound bilateral sensorineural hearing loss. It usually manifests as syncope following sympathetic activation.6,18 Timothy syndrome (LQTS type 8) is associated with pathogenic variants in CACNA1C and is characterized by atrioventricular conduction disturbances, tachyarrhythmias, congenital heart defects, hand/foot and facial dysmorphism, neurodevelopmental problems and autism spectrum disorder.6,19 Andersen-Tawil syndrome (LQTS type 7), associated with pathogenic variants of KCNJ2, besides prolonged QTc is characterized by the presence of U waves, hypokalemic periodic paralysis, facial dysmorphism and mild neurocognitive deficits, and regularly presents with palpitations, syncope, or periodic paralysis triggered by prolonged rest or rest following exertion.6,20

Genetic testing and genetic counseling are recommended in all individuals diagnosed as having or with a strong clinical suspicion of LQTS (class I),2,3 and may be considered in asymptomatic individuals with QTc >460 ms (prepuberty) or >480 ms (adults), in the absence of secondary causes (class IIb)2 (Table 1).

SQTS is diagnosed in the presence of QTc ≤340 ms (class I), and should be considered (class IIa) in the presence of QTc ≤360 ms and one or more of the following: a confirmed pathogenic mutation; a family history of SQTS; a family history of SD at age <40 years; or survival from a VT/VF episode in the absence of structural heart disease.9

SQTS is associated with variants in three genes coding for potassium channels (KCNH2, KNCQ1 and KCNJ2), which are also associated with LQTS, although with the opposite effect in terms of functional alterations.6,10

Genetic testing may be considered in individuals with SQTC (class IIb)2,3 to facilitate screening of first-degree relatives.3 Unlike in LQTS, genetic testing has no prognostic value in SQTS.

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a hereditary arrhythmogenic syndrome that typically manifests with adrenergically mediated syncope or SD secondary to VT.21 Diagnosis is established by in the presence of a structurally normal heart, normal ECG and exercise- or emotion-induced bidirectional or polymorphic VT (class I) or in patients who are carriers of pathogenic mutation(s) in the genes RyR2 or CASQ2 (class I).9

Genetic testing is recommended in individuals with CPVT (class IIa3/class I2) (Table 1).

Hypertrophic cardiomyopathy (HCM) is defined by the presence of inappropriate left ventricular hypertrophy disproportionate to loading conditions or other cardiac or systemic factors sufficient to cause the observed anomaly. The diagnostic criterion is a maximum wall thickness of ≥15 mm in any left ventricular myocardial segment. In first-degree relatives, diagnosis is established by an otherwise unexplained wall thickness of ≥13 mm in any segment.25

Genetic testing (targeted or multiple gene panels) is recommended in patients with a clinical diagnosis of HCM (class I,2,25 class IIa,3,26 level A23), particularly when screening of family members is anticipated.25,26 Molecular diagnosis is also recommended when the clinical presentation suggests a particular genetic cause that is non-sarcomeric (class I).26

In patients fulfilling diagnostic criteria for HCM, genetic testing is positive in 30-60% of cases,25,27–29 higher in familial disease and lower in older patients and in those with non-standard clinical manifestations, including late onset, less severe hypertrophy, concentric hypertrophy or sigmoid septum, and absence of adverse events.25,28,29

Genetic testing in patients with a borderline diagnosis of HCM (left ventricular wall thickness 12-13 mm in adults; left ventricular hypertrophy in the presence of hypertension, athletic training, valve disease) should be performed only after detailed assessment by specialist teams (class IIa),25 since the result may also be equivocal: a negative result does not rule out the diagnosis and variants of uncertain significance are hard to interpret25 (Table 2).

Metabolic and other hereditary diseases account for a small, though important, proportion of patients with an HCM genotype. Conditions that more commonly cause HCM include Anderson-Fabry disease, Danon disease, amyloidosis and HCM caused by variants in the PRKAG2 gene. Differential diagnosis is crucial, since these diseases have very different natural history and prognosis, and may require different therapeutic approaches. Supplement 7 lists cardiac and extracardiac manifestations that can guide molecular diagnosis.

Dilated cardiomyopathy (DCM) is defined by the presence of left ventricular or biventricular dilatation and systolic dysfunction in the absence of abnormal loading conditions or coronary artery disease sufficient to cause the observed degree of dysfunction. It is considered phenotypically related to hypokinetic non-dilated cardiomyopathy (HNDC), which is defined by the presence of left ventricular or biventricular systolic dysfunction (defined as left ventricular ejection fraction <45%) without dilatation.24

As molecular diagnostic techniques have improved, 25-50% of cases of DCM previously thought to be idiopathic have been found to have a genetic basis, mainly with autosomal dominant transmission.24,30,31 A comprehensive investigation of family history in index cases, covering at least three generations, is thus essential. In the absence of conclusive molecular genetic information in a family, DCM or HNDC is considered to be familial if two or more family members are affected or in the presence of an index patient fulfilling diagnostic criteria for DCM/HNDC and a first-degree relative with autopsy-proven DCM and SD by the age of 50 years.24

However, the lack of a family history does not exclude a genetic cause, and the latter should be considered especially when there are atrioventricular conduction disturbances, prior to or concomitant with ventricular dysfunction or skeletal myopathy.30 Other diagnostic criteria are used for familial forms (Table S4, Supplement 8).24

Genetic testing is recommended (class I) for patients diagnosed with DCM and significant cardiac conduction disease ((i.e., first-, second-, or third-degree heart block) and/or a family history of premature unexpected SD,2 and in patients with a familial form of DCM or in sporadic DCM with clinical clues suggestive of a particular/rare genetic disease.24 Genetic testing should be considered in the most clearly affected person in a family (level of evidence A)23 (Table 2).

Supplement 9 lists some manifestations of rare genetic forms of DCM that should prompt molecular diagnosis.

Genetic testing has a positive result in 30-40% of cases of DCM,31 higher in familial than in isolated cases (25-40% vs. 10-25%).23

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is defined histologically by the progressive replacement of ventricular myocardium with adipose and fibrous tissue often confined to a ‘triangle of dysplasia’ comprising the right ventricular inflow, outflow, and apex.22 It is defined by the presence of right ventricular dysfunction (global or regional), with or without left ventricular disease, in the presence of histological evidence for the disease and/or abnormalities on ECG, echocardiography or cardiac magnetic resonance (CMR) (Table S5, Supplement 10).32

Although structural abnormalities predominate in the right ventricle, it is now known that involvement can be biventricular or even mainly in the left ventricle.33 There should be a high index of suspicion for this condition when non-ischemic late enhancement sparing the subendocardium is seen on CMR together with T-wave abnormalities on the ECG and ventricular arrhythmias, particularly in the presence of a family history of SD.34

When ARVC has been diagnosed in an index case, diagnosis in first-degree relatives requires only one of the following criteria: T-wave inversion in V1, V2 and V3 (over the age of 14 years); late potentials; VT with left bundle branch block morphology or >200 premature ventricular contractions in 24 hours; or mild right ventricular global or segmental dilatation or dysfunction.32

Comprehensive or targeted genetic testing can be useful for patients satisfying the diagnostic criteria for ARVC (class IIa2,3/level A23), and may be considered in possible cases (class IIb).2 The positivity rate for genetic testing in ARVC is usually around 50%35 (Table 2).

Restrictive cardiomyopathy (RCM) is rare and can be idiopathic, familial or secondary to systemic disorders. Characterized by a restrictive physiology, it is usually detected by echocardiography, which shows normal or reduced ventricular volumes and wall thicknesses that are not significantly increased (although wall thickness may be increased in infiltrative disease).22

Genetic testing may be considered for patients with HCM based on clinical history, family history, and electrocardiographic/echocardiographic findings (class IIb2/level B23) (Table 2).

Before genetic study is performed, differential diagnoses and specific diagnostic tests should be considered as listed in Supplement 11.

Left ventricular non-compaction (LVNC) is characterized by prominent left ventricular trabeculae and deep intertrabecular recesses with blood flow from the ventricular cavity and no communication with the coronary tree. Two layers of myocardium can be distinguished, compacted and non-compacted.22 In some individuals, LVNC is associated with ventricular dilatation and systolic dysfunction.22

It is not clear whether LVNC is a separate primary cardiomyopathy or merely a phenotypic trait shared by other cardiomyopathies and other pathological (neuromuscular and mitochondrial diseases and myopathies) and physiological conditions, including pregnancy and sports participation.23,36,37

There are various diagnostic criteria based on imaging studies (Table S6, Supplement 12).38–44

A diagnosis of cardiomyopathy is more likely when the quantitative short-axis echocardiographic criteria of Jenni38 or Jacquier43 are fulfilled together with one of the following factors: another affected family member (or family history of cardiomyopathy); ventricular dysfunction or wall motion abnormalities; symptoms or complications; neuromuscular disease; or one of several potentially causative genetic variants found in families with LVNC.45,46

Genetic testing may be considered for patients with a clinical diagnosis of LVNC based on clinical history, family history, and clinical (especially neuromuscular disease), electrocardiographic and echocardiographic findings (class IIa).2 It is not recommended in individuals with isolated LVNC or those without other abnormalities in ventricular structure or function, symptoms, or family history (Table 2).

There are two main sets of diagnostic criteria for FH: those of the Simon Broome Register Group51 and those of the Dutch Lipid Clinic Network.52 The criteria most often used in Portugal are adapted from those of the Simon Broome Register, as follows:

Genetic testing should be performed in individuals with definite or probable FH, as well as for their at-risk relatives, as recommended by the Journal of the American College of Cardiology expert panel.53

The test should include the genes LDLR, APOB and PCSK9, and whenever possible the genes associated with phenocopies of FH: LDLRAP1, APOE, LIPA, ABCG5 and ABCG8.53

Genetic testing provides prognostic information that can lead to more accurate risk stratification. Cascade screening of at-risk relatives is highly effective in identifying affected individuals who require appropriate treatment.

Individuals with confirmed FH, particularly those with homozygous FH, should be referred to a specialist in the condition. All FH patients should be offered a regular structured review that is carried out at least annually, since this can reduce cardiovascular morbidity and mortality through lifestyle interventions and prompt appropriate therapeutic measures.54

Pulmonary arterial hypertension (PAH) is defined as mean pulmonary arterial pressure >20 mmHg associated with pulmonary artery wedge pressure ≤15 mmHg and pulmonary vascular resistance ≥3 Wood units at rest, measured by right heart catheterization.57

Around 70-80% of patients with PAH inherited in an autosomal dominant pattern58 and 10-20% with sporadic or idiopathic PAH59 have variants in the BMPR2 gene, which codes for a protein in the TGF-β family. Penetrance is greater in females in these variants.60

Other genes have been associated with PAH, including TBX4, ATP13A3, GDF2, SOX17, AQP1, ACVRL1, SMAD9, ENG, KCNK3 and CAV1.58 Variants in EIF2AK4 are associated with pulmonary veno-occlusive disease/pulmonary capillary hemangiomatosis.61

Genetic testing and counseling should be offered to patients with hereditary or sporadic/idiopathic PAH. Genetic testing can identify asymptomatic carriers, but since penetrance is incomplete, it is currently impossible to predict who will develop the disease. Echocardiographic monitoring should be considered for such individuals.59,62 Identification of genetic variants in EIF2AK4 can avoid the need for pulmonary biopsy.58

Pre-implantation genetic diagnosis of PAH can enable selection of embryos for medically assisted reproduction.63