Hypertrophic cardiomyopathy: electrical abnormalities detected by the extended-length ECG and their relation to syncope

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Abstract

Background: Ventricular repolarization abnormalities can represent a trigger for lethal arrhythmias in hypertrophic cardiomyopathy (HCM). We sought to assess whether multiparametric computerized surface ECG analysis identifies repolarization abnormalities in HCM patients, and whether this approach allows identification of patients with syncope. Methods: In 28 HCM patients and 102 healthy subjects (14 and 51 males, mean age 44±15 and 41±14 years, respectively), 8-lead ECG (I, II, V1–V6) was recorded for 5 min, acquired in digital format and analyzed. Heart-rate corrected QT (QTc) and T wave complexity index (TWCc), QT dispersion, activation–recovery interval (ARI) and its dispersion, signal duration in the terminal portion of the filtered QRS at 25 Hz (LAS25 Hz) were analyzed among other parameters. Results: Compared to healthy subjects, HCM patients exhibited longer QRS, filtered QRS, QTc and QTd, greater TWCc, minor ARId and LA25 Hz. QRS duration and maximal septum thickness were linearly correlated (r=0.231 p<0.001). ARId shortening depended on ARI shortening in lead V1 (241±51 vs. 287±45, HCM vs. healthy subjects, p<0.0001) and lengthening in V6 (257±42 vs. 209±34, HCM vs. healthy subjects, p<0.0001). Significant factors for syncope at Wilks' stepwise discriminant analysis were TWCc, QRSd and LAS25 Hz (F=14.394, 10.098 and 9.226, respectively) with 92.3% positive predictive accuracy. Conclusions: In HCM, longer QRS and QT intervals are consequences of increased left ventricular mass, while ARI seems to reflect myocardial activation rather than inhomogeneity of recovery. The simultaneous evaluation of TWC, QRSd and LAS25 Hz, unable by itself to hold a predictive value, yielded high accuracy in predicting cardiogenic syncope.

Introduction

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disease and it is an important cause of disability and death in patients of all ages, although sudden and unexpected death in young people is perhaps the most devastating component of its natural history [1].

The clinical course for individual HCM patients is most appropriately viewed in terms of specific subgroups rather than only from perceptions of the overall spectrum of the disease. In fact, while most affected individuals remain asymptomatic or experience only paroxysmal manifestations [2], others die suddenly due to ventricular tachycardia or fibrillation. Abnormalities of ventricular repolarization can represent one of the triggers able to induce lethal arrhythmias [3].

Recently, together with well-known parameters such as QT interval and QT dispersion, newly developed indices have been introduced to explore ventricular repolarization, such as T-wave complexity and the activation–recovery index dispersion, whose clinical significance, however, is far from being completely understood.

We recently validated [4] the new noninvasive “extended-length electrocardiogram” (XL-ECG, Mortara Instruments, WI, USA) which allows, in a single recording, to simultaneously evaluate the parameters (QRS duration, QT dispersion, QT interval, T-wave complexity, activation recovery index dispersion) able to explore ventricular repolarization.

The aim of the present investigation was to assess whether patients with HCM, when compared to healthy subjects, exhibit changes in repolarization detectable non-invasively by this new computerized analysis of 12-lead ECG, and if this approach has a clinical application in discriminating between patients who experienced syncope and those who did not.

Section snippets

Methods

We enrolled 28 patients with HCM (14 males, mean age 44±15 years). All of them had an echocardiographic diagnosis of asymmetric hypertrophy on a septal thickness greater than 15 mm [5]. Four of them exhibited mild dynamic left ventricular outflow obstruction (peak outflow gradient under basal condition of 40, 34, 30, 30 mm Hg, respectively). As a control group, we used 102 healthy subjects (51 males, mean age 41±14) without remarkable past medical history and with normal physical examination,

Results

Echocardiographic data of HCM patients are reported in Table 1. The ECG patterns comprised increased QRS voltage in 16 patients, pathologic Q waves in 9, left and right bundle branch block in 2 and one, respectively. Six patients were on verapamil, six on beta-blockers and one on amiodarone. The presence of therapy was significantly correlated to the maximal interventricular septum thickness (r=0.59).

Eight patients reported a history of unexplained recurrent syncopal episodes (more than two in

Discussion

Longer QRS duration and prolonged QT interval are common findings in hypertrophic cardiomyopathy and data pertaining an increased risk of cardiac events related to these parameters [17], [18] should be considered cautiously. Likely, the increased left ventricular mass, in the QRS duration range of our population [19], determines longer QRS and QT intervals as suggested by the strict relationship between QRS duration and the maximal myocardial thickness. QT dispersion was also increased in our,

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