Original Article
Prognostic value of left ventricular mechanical dyssynchrony induced by exercise stress in patients with normal myocardial perfusion single-photon emission computed tomography

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Abstract

Background

Left ventricular mechanical dyssynchrony (LVMD) induced by exercise stress was reported to be clinically useful in detecting multivessel coronary artery diseases. The aim of this study was to compare the prognostic value of LVMD induced by pharmacological stress with that induced by exercise stress.

Methods

We retrospectively examined 918 consecutive patients who underwent exercise (N = 310) or pharmacological stress (N = 608) 99mTc-tetrofosmin single-photon emission computed tomography (SPECT) with normal myocardial perfusion. LVMD was evaluated by phase analysis as the indices of phase bandwidth and phase standard deviation (PSD).

Results

During the follow-up period (2.2 ± 1.9 years), 74 major cardiac events (MCEs) occurred (7 cases of cardiac death, 17 cases of heart failure, and 50 cases of coronary intervention). In global patients, the indices of LVMD on rest images were significantly greater in patients with MCEs (bandwidth (°): 51 ± 31 vs 37 ± 21, P = .001, PSD: 14 ± 9 vs 10 ± 6, P = .001). The exercise stress bandwidth was significantly higher in patients with MCEs (62 ± 37° vs 42 ± 21°, P = .026), as was the pharmacological stress bandwidth (57 ± 35° vs 43 ± 24°, P = .006). Multivariate analysis demonstrated the exercise stress bandwidth to be an independent predictor of MCEs (HR 1.017, CI 1.003 to 1.032, P = .019), but the pharmacological stress bandwidth had no influence on MCEs.

Conclusions

LVMD induced by exercise stress was an independent predictor of MCEs in patients with normal perfusion SPECT, whereas that induced by pharmacological stress had no association with further events.

Introduction

Left ventricular mechanical dyssynchrony (LVMD) is a conduction disturbance characterized by a wide QRS duration on electrocardiography. The degree of LVMD was analyzed by tissue Doppler imaging (TDI) assessed by echocardiography. Myocardial perfusion single-photon emission computed tomography (SPECT) (MPS) is able to analyze LVMD quantitatively by phase analysis.1 The indices of LVMD, such as phase standard deviation (PSD) and phase bandwidth, are well correlated with those measured by tissue Doppler imaging.2, 3, 4 The prognostic value for major cardiac events (MCEs) of LVMD was previously demonstrated in asymptomatic women,5 patients with systolic heart failure,6 and in those with acute coronary syndrome.7

Normal stress MPS findings are associated with low-cardiac event risk.8 Myocardial perfusion sometimes globally reduces in patients with multivessel coronary artery diseases (CAD). Thus, there are some underestimated cases when MPS has no signs of cardiac ischemia. In those cases LVMD induced by exercise stress has diagnostic value in the detection of multivessel CAD.9 However, it is unknown whether LVMD induced by pharmacological stress (hyperemic drugs) is associated with future events. In this study, we retrospectively investigated whether LVMD induced by exercise or pharmacological stress has prognostic value in patients with normal myocardial perfusion.

Section snippets

Study Population

We retrospectively examined 918 consecutive patients who underwent exercise (N = 310) or pharmacological stress (N = 608) 99mTc-tetrofosmin SPECT. All patients were scheduled to undergo stress-rest ECG-gated MPS due to possible or definite CAD. Patients with bundle branch block on electrocardiography and abnormal MPS (summed stress score ≥ 3) were excluded from this study. The endpoint was the incidence of MCEs consisting of cardiac death, non-fatal myocardial infarction, hospitalization due to

Clinical Characteristics of the Patients

The characteristics of the study population are shown in Table 1. The mean age was 70 ± 12 years and the mean LVEF was 71 ± 11%. SSS, SRS, and SDS were .3 ± .7, .2 ± .6, and .2 ± .6, respectively. The QRS duration on electrocardiography was 98.0 ± 9.5 ms. Based on these results, all patients had neither evidence of cardiac ischemia on MPS nor notable LVMD on electrocardiography.

Comparison Between Exercise and Pharmacological Stress

The characteristics of patients with exercise and pharmacological stress are shown in Table 2. Those with

Discussion

This is the first study to describe the prognostic value of bandwidth on exercise stress as an index of LVMD in patients with no evidence of cardiac ischemia. LVMD induced by exercise stress was associated with further cardiac events, whereas that induced by pharmacological stress was not.

LVMD is evaluated by the QRS duration on electrocardiography or by TDI assessed by echocardiography. Phase analysis on MPS is also one of the methods for evaluating LVMD. Heart Function View evaluates the

Conclusions

LVMD induced by exercise stress was an independent predictor of cardiac events in patients with normal perfusion SPECT, whereas that induced by pharmacological stress had no association with further events.

Disclosures

Drs Tomohiko Sakatani, Takeru Kasahara, Daisuke Irie, Yoshinori Tsubakimoto, Akiko Matsuo, Hiroshi Fujita, Keiji Inoue have no conflicts of interest to declare.

Funding

Not applicable.

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All editorial decisions for this article, including selection of reviewers and the final decision, were made by guest editor Saurabh Malhotra, MD, MPH.

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