Abstract
Myocardial perfusion scintigraphy (MPS) is a valuable diagnostic tool for identifying stable angina and evaluating myocardial viability. In clinical practice, MPS-based analysis tools, such as the Heart Risk View (Nihon Medi-physics Co., Ltd., Tokyo, Japan), have proven effective in assessing left ventricular (LV) dyssynchrony. This case report illustrates the diagnostic utility of MPS in identifying and assessing LV dyssynchrony due to ventricular septal pacing for pacemaker implantation. Upon admission, the patient exhibited symptoms of heart failure (New York Heart Association Class II) due to a Wenckebach-type second-degree atrioventricular block, requiring dual-chamber pacemaker implantation with septal pacing. Eight months postoperatively, phase analysis using the Heart Risk View revealed a significantly reduced ejection fraction (EF: 30 %) and marked LV dyssynchrony [standard deviation width (PhSD): 86 degrees, histogram bandwidth (PhBW): 227 degrees]. Given the presentation of drug-resistant heart failure and asynchronous contraction, a cardiac resynchronization therapy (CRT) device was implanted. Immediately following CRT implantation, phase analysis demonstrated notable improvement in LV function (EF: 42 %) and LV dyssynchronous contraction (PhSD: 30 degrees, PhBW: 110 degrees).
Learning objective
This study investigated the utility of myocardial perfusion scintigraphy in diagnosing post-implantation dyssynchronous contractions and assessing treatment efficacy. This case underscores the potential for dyssynchrony due to ventricular pacing. It emphasizes the importance of regular reassessment for mechanical dyssynchrony, particularly in patients experiencing a severe decline in ejection fraction or exercise tolerance following pacemaker implantation. Early evaluation is crucial to determine the need for cardiac resynchronization therapy and prevent further deterioration.
Keywords: Left ventricular mechanical dyssynchrony, Single photon emission computed tomography, Cardiac resynchronization therapy
Introduction
Left ventricular (LV) dyssynchrony, often induced by right ventricular pacing, is a recognized contributing factor to heart failure [1]. Previous studies have shown the efficacy of phase standard deviation (PhSD) [normal range: 25.6 ± 9.7 degrees (6.2–45.0)] and histogram bandwidth (PhBW) [normal range: 6.9 ± 2.6 degrees (1.7–12.1)] as analytical tools for detecting LV dyssynchrony [2,3]. Myocardial perfusion scintigraphy (MPS) utilizing the Heart Risk View function (Nihon Medi-physics Co., Ltd., Tokyo, Japan) has demonstrated reproducible results in LV dyssynchrony evaluation [4], which we believe is also effective for dyssynchrony from pacemaker implantation. Prior reports have documented cases of heart failure exacerbation secondary to septal pacing [5]. The present case describes a patient presenting with LV dyssynchrony due to dual-chamber (DDD) pacemaker implantation with ventricular septal pacing. Despite these challenges, the patient was successfully treated with cardiac resynchronization therapy (CRT). This study aims to highlight the utility of MPS in evaluating mechanical dyssynchrony caused by right ventricular pacing and in assessing the therapeutic efficacy of CRT.
Case Report
The patient was an 84-year-old male with a history of coronary artery bypass surgery 10 years previously as well as chronic heart failure, who was referred to our institution for acute onset fatigue due to ventricular block. His physical activity level was classified as New York Heart Association (NYHA) class II, and initial 12‑lead electrocardiography (ECG) revealed 47 bpm with Wenckebach type II atrioventricular block. Chest radiography exhibited mild cardiac dilation, with a cardiac-to-thoracic ratio of 54.1 %. Transthoracic echocardiography (TTE) demonstrated impaired wall motion at the base of the septum, with a preserved ejection fraction (EF) of 58 % and LV end-systolic volume (ESV) of 65 mL, consistent with his findings 10 years previously. Additionally, laboratory examination indicated a B-type natriuretic peptide (BNP) level of 160 pg/mL, while computed tomography showed no significant stenosis of the coronary arteries or bypass grafts.
In accordance with the Japanese guidelines for managing Wenckebach-type symptomatic second-degree atrioventricular blocks, a DDD pacemaker was deemed an essential intervention, with the septum as the optimal pacing site (QRS width: 166 ms; Fig. 1A). Following pacemaker implantation, 99mTc-tetrofosmin quantitative gated MPS was performed 30 min after each administration using 99mTc-tetrofosmin 16-frame data acquisition.
Fig. 1.
(A) 12‑lead electrocardiogram (ECG) showed an HR of 60 ppm. (B) 12‑lead ECG showed an HR of 75 ppm 8 months after dual-chamber pacemaker implantation. (C) 12‑lead ECG showed HR of 75 ppm after cardiac resynchronization therapy.
With respect to myocardial perfusion, quantitative gated single photon emission computed tomography (SPECT) (QGS) assessment demonstrated perfusion reduction in the central region of the anterior septum, with a summed stress score (SSS) of 10 points, a summed rest score (SRS) of 8 points, and a summed differential score (SDS) of 2 points.
Phase analysis was further conducted using the Heart Risk View software. The cardiac cycle was divided into 16 frames, while a tolerance range of ±20 % of the mean R-R interval was set for the gate, and the resting image data set was used for analysis. Short-axis tomographic images were processed using Heart Risk View software to evaluate the position of the LV inner edge, revealing a PhSD of 20 degrees and PhBW of 73 degrees (Fig. 2). The anaerobic threshold (AT) during cardiopulmonary exercise testing (CPX) increased to 2.6 metabolic equivalents (METs), although no ischemic changes were observed on ECG.
Fig. 2.
The clinical indicators after dual-chamber pacemaker implantation, before and after cardiac resynchronization therapy are shown. At the bottom, the phase analysis using Heart Risk View at each stage and the values of phase standard deviation (PhSD) and histogram bandwidth (PhBW) are shown.
PM; pacemaker, CRT; cardiac resynchronization therapy, ESV; end-systolic volume, EF; ejection fraction, BNP; brain natriuretic peptide.
Eight months after pacemaker implantation, the patient experienced respiratory deterioration (NYHA class III). ECG showed a QRS width of 172 ms (Fig. 1B), and TTE demonstrated increased LV volume, reduced LVEF (ESV: 71.4 mL, LVEF: 46 %), and septal flush motion was shown. Laboratory testing revealed an elevated BNP level of 347 pg/mL, while coronary angiography ruled out any possible lesions. Furthermore, adenosine MPS exhibited an SSS of 9 points, an SRS of 8 points, and an SDS of 1 point, with no notable alterations in myocardial perfusion. However, phase analysis revealed a PhSD of 85 degrees and PhBW of 227 degrees (Fig. 2). Although the heart failure team decided to gradually increase the dosage of the pharmaceutical agent up to the maximum tolerated dose according to the guidelines, his BNP level increased to 1636 pg/mL, with no improvement in TTE (ESV: 94.0 mL, LVEF: 31 %). Consequently, the patient was deemed an appropriate candidate for CRT device implantation; in order to match phase of the lateral wall, the LV lead was implanted on the left posterior wall of the left ventricle, which was performed 14 months after the initial procedure.
Following CRT with biventricular pacing (Fig. 1C), TTE exhibited still septal flush motion, however, resting MPS and phase analysis demonstrated significant improvements in dyssynchrony (PhSD: 30 degrees, PhBW: 110 degrees) (Fig. 2). In addition, the patient's BNP level decreased to 147 pg/mL, and the AT during CPX reached 2.8 METs, which was identical to the level observed at the time of pacemaker implantation. TTE obtained 3 months post-CRT revealed improvements in both LV volume and LVEF (ESV: 60.2 mL, LVEF: 42 %).
Discussion
Synchronization disorders encompass a wide spectrum of conditions, including intraventricular, atrioventricular, and interventricular conduction disturbances. While right ventricular pacing is a well-established and effective treatment for bradycardia, it can precipitate deterioration in patients with heart failure by inducing intraventricular conduction defects [6]. As such, clinical decision-making between septal pacing and apical right ventricular pacing for the prevention of conduction disorders remains a debated topic [7]. CRT has emerged as a valuable intervention for heart failure refractory to medical therapy by directly addressing the intraventricular conduction defects [8]. Traditionally, QRS width assessment is recommended by current guidelines to identify the presence of conduction defects. Other parameters, such as QRS waveform, exercise tolerance, and EF, are then considered when determining if a patient is a candidate for CRT. Although studies have evaluated pacemaker-induced intraventricular conduction disturbances using ECGs and echocardiograms, there has been no established method of evaluation.
Chen et al. [2] designed a phase analysis-derived histogram illustrating the phase angle distribution of the LV at all sample points, suggesting that this function could provide quantitative indices of LV mechanical dyssynchrony. Other studies have reported on the standardized and highly reproducible results of phase analysis using MPS [3,9]. Nakajima et al. [9] established the mean values and ranges for the parameters used in the Heart Risk View, which were used in the present study. In our study, upon the patient's readmission for respiratory deterioration, distinct alteration in the phase analysis of MPS was shown. Although there is currently no established diagnostic method for asynchrony, this case emphasizes the diagnostic utility of scintigraphy for the early diagnosis of post-implantation conduction disorders. In this case, the patient's history of heart bypass surgery may have contributed to the development of intraventricular dyssynchrony. However, given the absence of effectiveness with beta-blockers, it was postulated that the primary cause was induced from the mechanical changes following right ventricular pacing. Following the introduction of CRT, improvements were observed in both cardiac morphology and phase analysis.
This case report is limited by several factors. Firstly, the observation period was short, necessitating further investigation into the long-term effectiveness of the treatment. Additionally, further research is required to confirm whether SPECT is an accurate indicator of dyssynchronous contraction in response to CRT.
In conclusion, this case highlights the importance of MPS with Heart Risk View analysis in diagnosing intraventricular dyssynchrony. In patients with suspected conduction defects and deteriorating heart failure, phase analysis could be considered, especially when traditional ECG and TTE assessments are inconclusive. Furthermore, MPS with phase analysis functions could be useful in guiding treatment decisions and evaluating the efficacy of CRT.
Consent statement
The authors confirm that written consent for the submission and publication of this case report, including images and associated text, has been obtained from the patient in line with the COPE guidance.
Declaration of competing interest
The authors declare that there is no conflict of interest.
Acknowledgments
We would like to thank Editage (www.editage.jp) for English language editing.
References
- 1.Nogami A., Kurita T., Abe H., Ando K., Ishikawa T., Imai K., Usui A., Okishige K., Kusano K., Kumagai K., Goya M. JCS/JHRS 2019 guideline on non-pharmacotherapy of cardiac arrhythmias. Circ J. 2022;86:337–363. doi: 10.1253/circj.CJ-21-0162. [DOI] [PubMed] [Google Scholar]
- 2.Chen J., Garcia E.V., Folks R.D., Cooke C.D., Faber T.L., Tauxe E.L., Iskandrian A.E. Onset of left ventricular mechanical contraction as determined by phase analysis of ECG-gated myocardial perfusion SPECT imaging: development of a diagnostic tool for assessment of cardiac mechanical dyssynchrony. J Nucl Ann Nucl Cardiol. 2005;12:687–695. doi: 10.1016/j.nuclcard.2005.06.088. [DOI] [PubMed] [Google Scholar]
- 3.Tatsuno K., Okuda K., Nakajima K., Saito H., Shibutani T., Onoguchi M., Takahashi T., Mochizuki T., Watanabe N., Matoba M. Normal and range value evaluations using heart risk view-function based on the Japanese Society of Nuclear Medicine working group database. Ann Nucl Cardiol. 2022;8:51–56. doi: 10.17996/anc.22-00156. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Nakae I., Hayashi H., Matsumoto T., Mitsunami K., Horie M. Clinical usefulness of a novel program “heart function view” for evaluating cardiac function from gated myocardial perfusion SPECT. Ann Nucl Med. 2014;28:812–823. doi: 10.1007/s12149-014-0875-0. [DOI] [PubMed] [Google Scholar]
- 5.Yaegashi T., Furusho H., Chikata A., Usui S., Kaneko S., Yamagishi M., Takamura M. Separated right and left ventricular excitation during right ventricular septal pacing in a patient with narrow QRS wave: a case report. J Med Case Rep. 2014;8:158. doi: 10.1186/1752-1947-8-158. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Curtis A.B., Worley S.J., Adamson P.B., Chung E.S., Niazi I., Sherfesee L., Shinn T., St. John Sutton M. Biventricular pacing for atrioventricular block and systolic dysfunction. N Engl J Med. 2013;368:1585–1593. doi: 10.1056/NEJMoa1210356. [DOI] [PubMed] [Google Scholar]
- 7.Kikuchi M., Tanno K., Miyoshi F., Munetsugu Y., Onuma Y., Ito H., Adachi T., Kawamura M., Asano T., Kobayashi Y. Long-term effectiveness of right septal pacing vs. right apical pacing in patients with atrioventricular block. J Arrhythm. 2012;28:214–218. doi: 10.1016/j.joa.2012.04.001. [DOI] [Google Scholar]
- 8.Salukhe T.V., Dimopoulos K., Francis D. Cardiac resynchronization may reduce all-cause mortality: meta-analysis of preliminary companion data with CONTAK-CD. Int J Cardiol. 2004;93:101–103. doi: 10.1016/j.ijcard.2003.10.002. [DOI] [PubMed] [Google Scholar]
- 9.Nakajima K., Matsumoto N., Kasai T., Matsuo S., Kiso K., Okuda K. Normal values and standardization of parameters in nuclear cardiology: Japanese Society of Nuclear Medicine working group database. Ann Nucl Med. 2016;30:188–199. doi: 10.1007/s12149-016-1065-z. [DOI] [PMC free article] [PubMed] [Google Scholar]