Diagnosing a Primary Electrical Disorder

Making a diagnosis of an inherited primary electrical disorder in a patient who presents with palpitations, syncope, or a cardiac arrest can be challenging. Fortunately, a document was recently published that provides guidance: the HRS/EHRA/APHRS Expert Consensus Statement on the Diagnosis and Management of Patients with Inherited Primary Arrhythmia Syndromes by the Heart Rhythm Society (HRS), the European Heart Rhythm Association (EHRA) and the Asia Pacific Heart Rhythm Society.¹ The objective of this consensus document was to “provide clinical guidance for diagnosis, risk stratification and management of patients affected by inherited primary arrhythmia syndromes.” Interestingly, the authors of this consensus document acknowledge that there are no randomized or blinded studies in the field and that all of the recommendations are based on expert opinion only. Although the document is a comprehensive reference for both the diagnosis and treatment of inherited arrhythmias, portions of its content related just to diagnostic criteria have been cherry-picked and paraphrased below to create a modern summary of the diagnostic criteria for five key primary arrhythmia syndromes.  

Long QT Syndrome (LQTS) 

1. LQTS is diagnosed: 

• In the presence of an LQTS risk score ≥3.5² in the absence of a secondary cause for QT prolongation [see for scoring system] and/or
• In the presence of an unequivocally pathogenic mutation in one of the LQTS genes or
• In the presence of a QT interval corrected for heart rate using Bazett’s formula (QTc) ≥500 ms in repeated 12-lead electrocardiograms (ECG) and in the absence of a secondary cause for QT prolongation.

2. LQTS can be diagnosed in the presence of a QTc between 480–499 ms in repeated 12-lead ECGs in a patient with unexplained syncope in the absence of a secondary cause for QT prolongation and in the absence of a pathogenic mutation.

Brugada Syndrome (BrS)

1. BrS is diagnosed in patients with ST-segment elevation with type 1 morphology ≥2 mm in ≥1 lead among the right precordial leads V1, V2, positioned in the 2nd, 3rd or 4th intercostal space occurring either spontaneously or after provocative drug test with intravenous administration of Class I antiarrhythmic drugs.
2. BrS is diagnosed in patients with type 2 or type 3 ST-segment elevation in ≥1 lead among the right precordial leads V1, V2 positioned in the 2nd, 3rd or 4th intercostal space when a provocative drug test with intravenous administration of Class I antiarrhythmic drugs induces a type 1 ECG morphology.

Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT)

1. CPVT is diagnosed in the presence of a structurally normal heart, normal ECG, and unexplained exercise or catecholamine-induced bidirectional VT or polymorphic ventricular premature beats or VT in an individual <40 years of age.
2. CPVT is diagnosed in patients (index case or family member) who have a pathogenic mutation.
3. CPVT is diagnosed in family members of a CPVT index case with a normal heart who manifest exercise-induced premature ventricular contractions (PVCs) or bidirectional/polymorphic VT.
4. CPVT can be diagnosed in the presence of a structurally normal heart and coronary arteries, normal ECG, and unexplained exercise or catecholamine-induced bidirectional VT or polymorphic ventricular premature beats or VT in an individual >40 years of age.

Short QT syndrome (SQTS) 

1. SQTS is diagnosed in the presence of a QTc ≤330 ms. 
2. SQTS can be diagnosed in the presence of a QTc <360 ms and one or more of the following: a pathogenic mutation, family history of SQTS, family history of sudden death at age ≤40, survival of a VT/VF episode in the absence of heart disease.

Early Repolarization (ER)

1. ER syndrome is diagnosed in the presence of J-point elevation ≥1 mm in ≥2 contiguous inferior and/or lateral leads of a standard 12-lead ECG in a patient resuscitated from otherwise unexplained VF/polymorphic VT.
2. ER syndrome can be diagnosed in an SCD victim with a negative autopsy and medical chart review with a previous ECG demonstrating J-point elevation ≥1 mm in ≥2 contiguous inferior and/or lateral leads of a standard 12-lead ECG.
3. ER pattern can be diagnosed in the presence of J-point elevation ≥1 mm in ≥2 contiguous inferior and/or lateral leads of a standard 12-lead ECG.

This consensus document provides practical diagnostic criteria for a wide range of primary electrical disorders, and stresses the importance of performing serial electrocardiography and the need for an ECG abnormality to be reproducible before confirming a diagnosis. Unlike making a diagnosis of an arrhythmia in the electrophysiology laboratory, which usually depends on interpretation of the intracardiac recordings and the results of programmed stimulation, establishing a diagnosis of a primary electrical disorder is largely based on careful inspection and interpretation of the 12-lead ECG. This document is another reminder of the sustainable power of the simple, cost-effective, and underutilized surface 12-lead ECG, and the importance of expert interpretation.

References

1. Priori SG, Wilde AA, Horie M, et al. HRS/EHRA/APHRS Expert Consensus Statement on the Diagnosis and Management of Patients with Inherited Primary Arrhythmia Syndromes. Heart Rhythm. 2013 Aug 29;e75-e106.
2. Schwartz PJ, Moss AJ, Vincent GM, Crampton RS. Diagnostic criteria for the long QT syndrome. An update. Circulation. 1993;88:782-784.