Author + information
- Jean-Philippe Couderc, PhD, MBA∗ ( and )
- Wojciech Zareba, MD, PhD
- ↵∗Address for correspondence:
Dr. Jean-Philippe Couderc, Department of Cardiology, University of Rochester, 601 Elmwood Avenue, Box 653, Rochester, New York 14642.
The discrimination between long QT syndrome (LQTS) types and the ability to determine the presence of LQTS in these patients is of great importance and Porta-Sánchez et al. (1) deliver an interesting study in which computerized analyses of the T-wave morphology from the body-surface electrocardiogram (ECG) provides complementary information to QTc interval prolongation for the diagnosis of the syndrome. The ECG-based diagnosis of the LQTS remains a challenge today and not even experts in the field would feel confident diagnosing the presence of the LQTS and its type based only on the ECG tracings of their patients. Therefore, the role of the morphology of the T-wave and its value for subsequent clinical decision remains to be elucidated.
The work proposed by Porta-Sánchez et al. (1) in this issue of JACC: Clinical Electrophysiology, is a new study evaluating a set of digital quantifiers of T-wave morphology extracted from representative beats recorded from standard 12-lead ECG recordings. These ECG measurements primarily quantify visual characteristics of the T-wave including its asymmetry, flatness, and the presence of notching. Ultimately, these measures are combined into 1 single score. Although a lot of various efforts have been put into the development of methods to measure dynamic aspects of ventricular repolarization such as variability, lability, and alternans, Porta-Sánchez et al.’s (1) work confines itself to an analysis of the static characteristics of cardiac repolarization. The technology in question delivers a set of measures that quantify the T-wave signal patterns to reliably measure its morphology expanding the repolarization analysis beyond the QT/QTc interval duration or the durations of subsections such as the J point to Tpeak, or Tpeak-Tend intervals. It is certainly worth noting that the quantitative measurements of T-wave morphology is not by any means a novel idea (2). Indeed, numerous prior studies over the past decades (3–5) have also addressed the same challenge highlighted in the Porta-Sánchez et al. (1) work. These prior publications have also endorsed the complementarity of T-wave morphology to QTc length in discriminating the LQTS types (especially types 1 to 3).
Quantifying T-wave morphology is an intriguing approach to augment our understanding of cardiac channelopathies. Initially described by Moss et al. (6), the phenotype-genotype association between specific ion channel dysfunction and specific T-wave morphology has been a fascinating endeavor in which body-surface ECG became a tool to gain direct insights into cardiac ion currents and the overall electrical activity of the heart, a set of insights that genetic tests painfully lacks.
There are several reasons for investigating T-wave morphology. First of all, the association between the presence of QTc prolongation and a risk for life-threatening event is not perfect. Therefore, the use of T-wave morphology as complementary information to the QT/QTc interval prolongation is an attractive option. Unfortunately, this potential correlation remains unclear because of the scarcity of large datasets of digital ECGs from genetically confirmed LQTS patients. In the Porta-Sánchez et al. (1) work, the association between these ECG measurements and cardiac events is not presented but the plethora of scientific publications demonstrating association between specific LQTS types and event rates (7) and triggers (8) is rather convincing justifying the importance of clinically identifying the LQTS type. Hence, ECG-based technology represents a fast, readily available, and inexpensive (in comparison to genetic testing) solution for the patients and the clinicians.
The concealed form of LQTS is believed to be present in around 30% of the clinically identified cases. Such genotype-positive but phenotype-negative or borderline patients have been confirmed to be at risk for the occurrence of events and this group’s risk factors have been described previously (9). In this regard, Porta-Sánchez et al. (1) did provide insightful results by focusing their analysis on these LQTS type 1 and LQTS type 2 patients with a QTc interval <460 ms. Their results confirmed that these morphological parameters can complement the QTc interval prolongation in diagnosing LQTS (5), and also one may speculate that they could carry information about both an increased risk for cardiac events and a susceptibility to specific event triggers (8).
As a final comment, the role of both heart rate and gender is known to powerfully impact ventricular repolarization and its association with cardiac events. The study in question would have benefited from exploring the gender effect and its relationship with heart rate. It would have been interesting to look at these factors especially investigating sequential ECG recordings acquired in the same patient both on and off beta-blockers.
In conclusion, investigators need to challenge themselves to develop new ECG markers for the risk stratification of patients suspected to carry LQTS mutations. In this regard, the Sánchez-Porta et al. (1) study is a novel and useful investigation building on prior observations on the role of T-wave morphology as a complementary set of information to the QTc interval.
↵∗ Editorials published in JACC: Clinical Electrophysiology reflect the views of the authors and do not necessarily represent the views of JACC: Clinical Electrophysiology or the American College of Cardiology.
Drs. Couderc and Zareba have reported that they consult for and receive honoraria from and own equity in iCardiac Technologies Inc.
All authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
- 2017 American College of Cardiology Foundation
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