QRS Prolongation is Associated With High Defibrillation Thresholds During Cardioverter-Defibrillator Implantations in Patients With Hypertrophic Cardiomyopathy

Abstract

subgroup of patients with hypertrophic cardiomyopathy (HCM) is at a high risk of having ventricular tachycardia and/or ventricular fibrillation. The implantable cardioverter-defibrillator (ICD) is widely recognized as the most effective and essential therapy for this patient population. [1][2][3] It has been demonstrated that both appropriate and inappropriate ICD discharges are frequently observed in HCM patients, 1-3 and this might impair qualityof-life as well as reduce battery longevity. Class III antiarrhythmic agents such as amiodarone have the potential for reducing ICD shocks 4 and might improve patients' prognosis. Furthermore, class I agents are also used in HCM patients to control atrial fibrillation or reduce the pressure gradient in the left ventricular (LV) outflow tract or midventricle when an obstruction is present. [5][6][7] The combined use of antiarrhythmic agents and an ICD in patients with HCM, and the larger volume of myocardium (caused by hypertrophy of the left ventricle) might result in a high defibrillation threshold (DFT). However, the predictors of a high DFT in patients with HCM have not been fully characterized. Thus, the purpose of this retrospective study was to evaluate the factors causing a high DFT in patients with HCM and ventricular tachycardia/ventricular fibrillation. Methods Study SubjectsThe study population consisted of 23 consecutive patients with an established diagnosis of HCM who underwent initial implantation of an ICD with a standard transvenous lead system at the National Cardiovascular Center from 1997 through to 2005. ICDs were implanted for secondary prevention in 20 of 23 patients, defined by clinical sustained ventricular tachyarrhythmia or resuscitation from sudden cardiac death. HCM was diagnosed on the basis of echocardiographic criteria defined as the presence of LV hypertrophy in the absence of other causes of hypertrophy. These patients also met the definition and classification proposed by the 1995 World Health Organization/International Society and Federation of Cardiology Task Force. 8 All defibrillation leads were implanted by a left cephalic vein cutdown and positioned in the right ventricular apex. No patient had any prior pacemaker implantation, and 2 had permanent atrial fibrillation. Patients who were diagnosed with HCM who progressed to a dilated phase of HCM were excluded from the study. ICD Implantation and DFT TestingThe following ICD models were implanted: 7220C (n= 1), 7223Cx (n=6), 7227Cx (n=2), 7229Cx (n=5), 7271Cx (n=1), and 7273Cx (n=5), manufactured by Medtronic, Inc (Minneapolis, MN, USA); and the 1861 (n=3) manufac- QRS Prolongation is Associated With High Defibrillation Thresholds During Cardioverter-Defibrillator Implantations in Patients With Hypertrophic CardiomyopathyTakayuki Nagai, MD; Takashi Kurita, MD; Kazuhiro Satomi, MD; Takashi Noda, MD; Hideo Okamura, MD; Wataru Shimizu, MD; Kazuhiro Suyama, MD; Naohiko Aihara, MD; Junjiro Kobayashi, MD*; Shiro Kamakura, MD Background: Although high defibrillation threshold (DFT) is a...

Prognostic Implications of Defibrillation Threshold Testing in Patients With Hypertrophic Cardiomyopathy

“…However, some patients with rare structural heart diseases, concurrent specific drug therapies or severely depressed LV function are still perceived at risk for high DFT . Among these, HCM display a unique increase of LV mass that has been shown to affect DFT in some but not all previous investigations. Besides this conflicting evidence, HCM patients represent a small subgroup even in largest studies on DFT testing .…”

Impact of QRS Duration and Morphology on the Risk of Sudden Cardiac Death in Asymptomatic Patients With Aortic Stenosis

“…Second, among patients with QRS duration Ն120 ms, only those with LBBB or combined RBBB and left anterior fascicular block have an increased risk of cardiovascular events. Underlying mechanisms of SCD in relation to QRS duration in patients with chronic pressure load are uncertain but may reflect associations of increased QRS duration with: 1) adverse LV response to increased afterload above the changes in LV mass per se (20); 2) myocardial scarring due to chronic subendocardial ischemia and fibrosis (21), further supported by the association with incident myocardial infarction; and 3) a higher threshold for termination of spontaneously occurring ventricular tachycardia in the presence of longer QRS duration (22). The latter hypothesis is further supported by the fact that QRS morphology was, in patients with QRS duration Ն120 ms, more important for the risk of adverse outcome than that of QRS duration per se.…”

Fabry cardiomyopathy presenting with a high defibrillation threshold: A short case report

“…Rhythm and conduction abnormalities have been reported to exist in Fabry disease as a result of the glycosphingolipid storage in cardiomyocytes, conduction system cells, and endothelial cells [2]. As left ventricular hypertrophy is the most common manifestation of Fabry disease, the high DFTs observed in this patient may be attributable to myocardial hypertrophy, which is a well-known substrate of high DFTs [3].…”