Noninvasive coronary angiography using 64-slice spiral computed tomography in an unselected patient collective: Effect of heart rate, heart rate variability and coronary calcifications on image quality and diagnostic accuracy

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Abstract

Objective

The aim of this study was to assess the impact of heart rate, heart rate variability and calcification on image quality and diagnostic accuracy in an unselected patient collective.

Subjects and methods

One hundred and two consecutive patients with known or suspected coronary artery disease underwent both 64-MSCT and invasive coronary angiography. Image quality (IQ) was assessed by independent observers using a 4-point scale from excellent (1) to non-diagnostic (4). Accuracy of MSCT regarding detection or exclusion of significant stenosis (>50%) was evaluated on a per segment basis in a modified AHA 13-segment model. Effects of heart rate, heart rate variability, calcification and body mass index (BMI) on IQ and accuracy were evaluated by multivariate regression. IQ and accuracy were further analysed in subgroups of significant predictor variables and simple regression performed to calculate thresholds for adequate IQ.

Results

Mean heart rate was 68.2 ± 13.3 bpm, mean heart rate variability 11.5 ± 16.0 beats per CT-examination (bpct) and median Agatston score 226.5. Average IQ score was 2 ± 0.6 whilst diagnostic quality was obtained in 89% of segments. Overall sensitivity, specificity, PPV or NPV was 91.2%, 99.2%, 95.3% or 98.3%. According to multivariate regression, overall IQ was significantly related to heart rate and calcification (P = 0.0038; P < 0.0001). The effect of heart rate variability was limited to IQ of RCA segments (P = 0.018); BMI was not related to IQ (P = 0.52). Calcification was the only predictor variable with significant effect on the number of non-diagnostic segments (P < 0.0001).

In a multivariate regression, calcification was also the single factor with impact on diagnostic accuracy (P = 0.0049).

Conclusion

Whilst heart rate, heart rate variability and calcification all show an inverse correlation to IQ, severe calcium burden remains the single factor with translation of such effect into decrease of diagnostic accuracy.

Introduction

Thanks to rapid technical evolution, today, multislice spiral computed tomography (MSCT) yields the promise of ultimately replacing diagnostic conventional angiography in selected patients [1], [2]. In this pursuit, one of the foremost challenges remains the reduction of motion artefacts caused by the contraction of cardiac chambers. With severe calcification, blooming artefacts or obscuring of the entire vessel lumen represents another limitation to accurate detection of coronary stenosis.

Whilst 4-slice MSCT proved highly susceptible to motion or blooming artefacts [3], [4], [5], the progress from 4- to 16-slice CT conveyed a marked augmentation of spatial and temporal resolution. Such technical advance translated into improved accuracy for the detection of high grade stenosis [6], [7], [8], [9]. Thereby, 16-slice technology offered the potential to extend acceptable image quality to higher heart rates [5], [6], [10], [11]. However, despite obvious improvement, imaging at elevated heart rate was persistently less robust and led to an overall decline in diagnostic accuracy [9], [12], [13], [14], [15]. Notwithstanding the reduction of blooming artefacts, the same was true with abundant calcification [13], [15].

Lately, 64-slice CT scanners have been introduced, excelling at gantry rotation speeds of 330 ms and an unprecedented spatial resolution of isotropic 0.4 mm3. To date, this technology has proved a further enhancement of diagnostic accuracy at moderate heart rates or calcium scores [16], [17], [18], [19], [20], [21], [22]. Nevertheless, severe calcification has persistently been linked to a decrease of diagnostic accuracy [22], [23]. Also, recent studies have shown a relentless decline of image quality at higher heart rate [24], [25], [26], [27]. However, a conceivable impact of elevated heart beat on diagnostic accuracy has rarely been evaluated in a larger collective.

Therefore, the primary aim of this study was to assess the effect of higher heart rates on diagnostic accuracy of 64-slice coronary angiography. The impact of heart beat variability, calcification or body mass index was likewise considered.

Section snippets

Study population

From September 2004 to May 2005 we studied 102 consecutive patients that were scheduled for conventional coronary angiography (ICA) due to suspected coronary artery disease (CAD) or suspected progression of known CAD. All MSCT studies were performed 1 day prior to ICA. Exclusion criteria for our study were artrial fibrillation, chronic congestive heart failure (NYHA III–IV), renal insufficiency (creatinine > 1.5 mg/dl), hyperthyroidism (basal TSH < 0.03 μl/l), known allergic reaction to iodinated

Study population

64-Slice CT was successfully performed in 102 consecutive patients scheduled for conventional coronary angiography. Clinical characteristics of the patients are summarized in Table 1. Classification of patients according to heart rate, heart rate variability and calcium burden resulted in a significant number of subjects with heart rates > 65 beats per minute (bpm; 48%), heart rate variability > 12 beats per CT-examination (bpct; 21%) or Agatston score > 400 (37%).

Overall, 1300 of 1326 segments could

Discussion

When compared to 16-slice CT, 64-slice technology excels at decreased gantry rotation time and thus allows considerable enhancement of temporal resolution to 165 or 83 ms (210 or 105 ms with 16-slice CT). By means of faster volume coverage, overall scan time is likewise shortened to 8–11 s, hence making the examination more robust against respiratory artefacts or patient movement. Furthermore, spatial resolution is improved to 0.4 mm and thereby blooming artefacts related to calcification may be

Study limitations

The present study is limited by a relatively small number of patients examined in a single centre. Since all patients were referred to our centre for catheterization, there is a considerable patient selection bias in our series with a prevalence of significant CAD of 62.7%.

The study design suffers from a lack of direct comparison to previous MSCT generations; thus greater robustness which was found for image quality may potentially be attributed to different population variables.

The primary

Conclusion

In conclusion, we show that despite a persistent inverse correlation of image quality to patient heart rate or heart rate variability, in 64-slice CT, there is no translation of such effect into deterioration of accuracy. With regard to better image quality at lower heart rate, the administration of beta-blockers still seems to be recommended but the dogma of aggressive heart rate reduction must be called into question or new thresholds be defined.

In an unselected patient population, abundant

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