Combination of Commonly Examined Parameters Is a Useful Predictor of Positive ^{99 m}Tc-Labeled Pyrophosphate Scintigraphy Findings in Elderly Patients With Suspected Transthyretin Cardiac Amyloidosis

Abstract

Background: A recent study revealed a high prevalence of transthyretin (TTR) cardiac amyloidosis (CA) in elderly patients. ^{99 m}Tc-labeled pyrophosphate (^{99 m}Tc-PYP) scintigraphy is a remarkably sensitive and specific modality for TTR-CA, but is only available in specialist centres; thus, it is important to raise the pretest probability. The aim of this study was to evaluate the characteristics of patients with ^{99 m}Tc-PYP positivity and make recommendations about patient selection for ^{99 m}Tc-PYP scintigraphy.

Methods and Results: We examined 181 consecutive patients aged ≥70 years who underwent ^{99 m}Tc-PYP scintigraphy at Kumamoto University Hospital between January 2012 and December 2018. Logistic regression analyses showed that high-sensitivity cardiac troponin T (hs-cTnT) ≥0.0308 ng/mL, left ventricular posterior wall thickness ≥13.6 mm, and wide QRS (QRS ≥120 ms) were strongly associated with ^{99 m}Tc-PYP positivity. We developed a new index for predicting ^{99 m}Tc-PYP positivity by adding 1 point for each of the 3 factors. The ^{99 m}Tc-PYP positive rate increased by a factor of 4.57 for each 1-point increase (P<0.001). Zero points corresponded to a negative predictive value of 87% and 3 points corresponded to a positive predictive value of 96% for ^{99 m}Tc-PYP positivity.

Conclusions: The combination of biochemical (hs-cTnT), physiological (wide QRS), and structural (left ventricular posterior wall thickness) findings can raise the pretest probability for ^{99 m}Tc-PYP scintigraphy. It can assist clinicians in determining management strategies for elderly patients with suspected CA.

Cardiac amyloidosis (CA) is a secondary cardiomyopathy with a hypertrophic appearance caused by deposition of anomalous fibrillar proteins in the myocardial extracellular matrix that originated from a precursor-altered protein called amyloid.¹ There are 3 main types of CA: acquired monoclonal immunoglobulin light chain amyloidosis (AL amyloidosis); mutant transthyretin (TTR) amyloidosis (ATTRm); and wild-type transthyretin amyloidosis (ATTRwt). ATTRwt is becoming increasingly recognized because of aging of populations, advancements in the understanding of the disease’s pathobiology, and the potential benefit from emerging therapies.² It has been reported that 13% of elderly patients (mean age, 82 years) who have heart failure with preserved ejection fraction (HFpEF) are diagnosed with ATTRwt.³ Several postmortem studies found cardiac amyloid deposition in up to 25% of individuals over 80 years of age.⁴

The precise diagnosis of CA requires endomyocardial biopsy (EMB) to demonstrate disease-specific deposition. However, EMB is a relatively invasive procedure⁵ and so cannot be performed routinely, especially in elderly patients.

A recent systematic evaluation of bone scintigraphy suggested that ^{99 m}Tc-labeled pyrophosphate (^{99 m}Tc-PYP) scintigraphy is remarkably sensitive and specific for imaging TTR-CA and reliably distinguishes it from other cardiomyopathies that mimic amyloidosis such as hypertrophic cardiomyopathy.^{6 99 m}Tc-PYP scintigraphy has emerged as the first-line modality for identifying TTR-CA. Nonbiopsy-based diagnosis of TTR-CA with bone scintigraphy has been proposed.⁷ However, because ^{99 m}Tc-PYP scintigraphy is costly and only available in specialist centers, it is important to raise the pretest probability.

Electrocardiography (ECG), echocardiography, and laboratory examination are valuable screening tests for detecting CA. Low voltage in limb leads, poor R progression in the precordial leads, and pseudo-infarct patterns on ECG and concentric thickening of the left ventricular (LV) wall with increased echogenicity and thickened valve leaflets on echocardiography are well-known findings that are suspicious for CA.¹ In addition, we have previously reported that high serum levels of high-sensitivity cardiac troponin T (hs-cTnT) are highly suggestive of CA, allowing its differentiation from cardiac hypertrophy of other etiologies.⁸

Therefore, we hypothesized that a combination of biochemical (laboratory examination), physiological (ECG), and structural (echocardiography) findings could raise the pretest probability of diagnosing TTR-CA with ^{99 m}Tc-PYP scintigraphy. The aim of this study was to evaluate the characteristics of patients who are ^{99 m}Tc-PYP-positive and make recommendations about patient selection for ^{99 m}Tc-PYP scintigraphy to diagnosis TTR-CA in the elderly using minimally invasive and widely used examinations such as hs-cTnT, ECG, and echocardiography.

Methods

Study Population

We enrolled consecutive patients aged ≥70 years referred to Kumamoto University Hospital on suspicion of CA, and who underwent ^{99 m}Tc-PYP scintigraphy between January 2012 and December 2018. Data including demographic characteristics, comorbidities, clinical signs, laboratory results, electrocardiographic and echocardiographic data, pathological findings, and treatment were obtained. Patients without electrocardiographic, echocardiographic, or laboratory data at diagnosis and patients with ventricular pacing were excluded. ^{99 m}Tc-PYP scintigraphy imaging, electrocardiography, echocardiography, and laboratory examinations were performed while the patient was in a clinically stable, noncongested condition. In this study, ^{99 m}Tc-PYP scintigraphy was performed at physician discretion. Tissue biopsy and DNA analysis for TTR mutations were performed in selected cases. The diagnosis of amyloid deposition was based on Congo red staining and apple-green birefringence with cross-polarized light microscopy.

The study conformed with the principles outlined in the Declaration of Helsinki. It was approved by the institutional review board and ethics committees of Kumamoto University (no. 2334). The requirement for informed consent was waived because of the low-risk nature of this retrospective study and the inability to obtain consent directly from all subjects. Instead, we extensively announced this study protocol at Kumamoto University Hospital and on our website (http://www.kumadai-junnai.com) and gave patients the opportunity to withdraw from the study.

^{99 m}Tc-PYP Scintigraphy Protocol

^{99 m}Tc-PYP scintigraphy was performed using a GE Discovery 670 dual-headed single-photon emission computed tomography/computed tomography camera with low-energy, high-resolution collimators (GE Healthcare, Waukesha, WI, USA). We administered 10–15 mCi (370–555 MBq) of ^{99 m}Tc-PYP (FUJIFILM, RI, Pharma, Tokyo, Japan) intravenously. Anterior and lateral planar views of the heart were obtained 3 h after the administration of the radiotracer. The image acquisition time was 5 min, matrix size was 256×256, and the energy window was set at 140 keV (±10%). Scans were performed and interpreted by experienced nuclear cardiologists blinded to the subjects’ cohort assignment. ^{99 m}Tc-PYP scintigraphy was scored by a single reader (S.S.) using the following grading system: grade 0, no cardiac uptake; grade 1, mild uptake less than bone; grade 2, moderate uptake equal to bone; and grade 3, high uptake greater than bone.^{9 99 m}Tc-PYP positivity was defined as a visual score of 2 or 3.

Biomarker Analysis

The median duration between laboratory examination and ^{99 m}Tc-PYP scintigraphy was 5 days (interquartile range [IQR], 1–10 days). Serum hs-cTnT levels were measured using the Elecsys 2010 Troponin T-high sensitive kit (Roche Diagnostics, Indianapolis, IN, USA).¹⁰ Plasma B-type natriuretic peptide levels were measured using a commercially available assay (Abbott Japan, Matsudo, Japan). We did not examine N-Terminal pro-B-type natriuretic peptide levels in this study. The estimated glomerular filtration rate was calculated using the Modification of Diet in Renal Disease formula.¹¹

ECG Analysis

ECG was performed after 10 min of rest while supine as part of the initial screening (frequency range 0.05–150 Hz, 25 mm/s, 10 mm/mV, Cardiofax G ; Nihon Kohden, Tokyo, Japan). In patients who had undergone a surgical procedure or pacemaker implantation, ECG was performed prior to the procedure. If no preprocedural ECG data were available, patients were excluded from the analysis. The median duration between ECG and ^{99 m}Tc-PYP scintigraphy was 7 days (IQR, 3–14 days). Measurements included the RR, QT, and QRS intervals, which were automatically analyzed. Wide QRS was defined as ≥120 ms.¹² Complete left bundle branch block, complete right bundle branch block, or interventricular conduction delay was defined according to standard published criteria.¹³ Low voltage in the limb leads was defined as QRS amplitude <5 mm in height in all limb leads. Poor R progression was defined as loss or absence of R waves in leads V1–3.¹⁴ The 2 ECG reviewers (K.M. and S.T.) were blinded at all times to the patient’s clinical history and data to minimize bias.

Echocardiographic Analysis

Echocardiography was performed using commercially available ultrasound equipment. The median duration between echocardiography and ^{99 m}Tc-PYP scintigraphy was 8 days (IQR, 4–16 days). Pericardial effusion, chamber size, wall thickness, and left ventricular ejection fraction (LVEF) were evaluated using standard procedures¹⁵ Peak early and late diastolic velocity of LV inflow (E and A velocity, respectively), deceleration time of E velocity, and peak early diastolic velocity on the septal corner of the mitral annulus (e′) were measured in the apical 4-chamber view and the E/e′ ratio was calculated.¹⁶ Asymmetric septal hypertrophy was defined by an interventricular septum to LV posterior wall thickness ratio ≥1.3.¹⁷ Concentric hypertrophy was based on LV posterior wall ≥11 mm and interventricular septum thickness ≥11 mm.¹⁸ LV mass indexed to body surface area was calculated using a previously described formula for hypertensive patients LV mass: {0.8×1.04×[(LV end-diastolic diameter+intraventricular septum thickness+LV posterior wall thickness)³−LV end-diastolic diameter³]+0.6}/body surface area.¹⁹ A restrictive LV filling pattern was defined as a ratio of early to late transmitral velocity >1.5 or E-wave deceleration time <130 ms.²⁰ The 2 echocardiography reviewers (M.Y. and K.H.) were blinded at all times to the patient’s clinical history and data to minimize bias.

Statistical Analysis

Continuous variables are presented as mean±standard deviation. Unpaired t-tests were used to compare groups. Nonnormally distributed variables are presented as medians (IQR). Non-continuous and categorical variables are presented as frequencies or percentages and compared using the χ² test. Receiver-operating characteristic (ROC) curve analysis was performed to compare the diagnostic accuracy and determine the hs-cTnT and LV posterior wall thickness cutoff values for ^{99 m}Tc-PYP scintigraphy positivity. Univariate logistic regression was performed to identify significant parameters related to ^{99 m}Tc-PYP scintigraphy positivity. Next, stepwise multivariate logistic regression analysis was performed. Stepwise selection with P=0.1 for backward elimination was used to select the best predictive model. All statistical tests were two-sided. P<0.05 was regarded as statistically significant. Statistical analysis was performed with the Statistical Package for Social Sciences, version 24 (SPSS, Chicago, IL, USA). One author (S.T.) had full access to all the data in the study and was responsible for its integrity and the data analysis.

Results

Baseline Clinical Characteristics

A total of 441 patients underwent ^{99 m}Tc-PYP scintigraphy at Kumamoto University Hospital between January 2012 and December 2018. After excluding patients aged <70 years and those with missing clinical data, 181 patients (men, 127; women, 54 [30%]) met the inclusion criteria and were included in the analysis (Figure 1). The mean LVEF was 55%. The number of patients with visual ^{99 m}Tc-PYP score of 0, 1, 2, and 3 was 65, 46, 39, and 31, respectively.

Figure 1.

Study flow chart detailing the inclusion and exclusion criteria for study patients. Enrolled patients were divided into 2 groups based on ^{99 m}Tc-PYP-scintigraphy results. ^{99 m}Tc-PYP, ^{99 m}Tc-labeled pyrophosphate.

We divided the patients into a ^{99 m}Tc-PYP negative group (n=111) and a ^{99 m}Tc-PYP positive group (n=70). Baseline characteristics of these groups are summarized in Table 1. Patients in the ^{99 m}Tc-PYP positive group were more likely to be male (P=0.003) and had higher hs-cTnT (P=0.004), longer PR duration (P<0.001), longer QRS duration (P=0.044), thicker intraventricular septal (P<0.001) and LV posterior wall (P<0.001) thickness, and shorter E-wave deceleration time (P=0.002) than the ^{99 m}Tc-PYP negative group. A total of 112 patients underwent tissue biopsy (e.g., heart, gastrointestinal tract, and subcutaneous tissue), of whom 53 patients (47%) underwent EMB. Among 49 patients in the ^{99 m}Tc-PYP negative group who underwent tissue biopsy, 9 (18%) had non-TTR amyloid deposition (AL amyloidosis, 7; inflammatory amyloidosis, 2). DNA analysis was performed for 1 patient (2.0%), who had ATTRm (Val30met [p.V50M] mutation). The patient with ATTRm had TTR amyloid deposition in the gastrointestinal tract and subcutaneous tissue but not in heart tissue. The clinical diagnoses of the patients in the ^{99 m}Tc-PYP negative group are shown in Figure 2. One-quarter of the patients in the ^{99 m}Tc-PYP negative group had hypertrophic cardiomyopathy (n=28, 25%), and nearly one-quarter had aortic stenosis (n=23, 21%).

Table 1. Baseline Characteristics of the Study Patients

	All (n=181)	99 mTc-PYP negative (n=111)	99 mTc-PYP positive (n=70)	P value
Age, years	79±6	78±6	80±6	0.087
Male sex, n (%)	127 (70)	69 (62)	58 (83)	0.003
NYHA functional class, n (%)				0.362
I	47 (26)	33 (30)	14 (20)
II	85 (47)	47 (42)	38 (54)
III	45 (25)	28 (25)	17 (24)
IV	4 (2.2)	3 (2.7)	1 (1.4)
Body mass index, kg/m2	22.0±3.6	21.5±3.6	22.3±2.8	0.126
Hypertension, n (%)	109 (60)	73 (66)	36 (51)	0.087
Diabetes mellitus, n (%)	48 (27)	30 (27)	18 (26)	0.846
Dyslipidemia, n (%)	61 (34)	42 (38)	19 (27)	0.138
Current smoker, n (%)	8 (4.4)	8 (7.2)	0	0.025
Atrial fibrillation, n (%)	63 (35)	39 (35)	24 (34)	0.907
Pacemaker implantation, n (%)	6 (3.3)	3 (2.7)	3 (4.3)	0.562
ICD implantation, n (%)	4 (2.2)	3 (2.7)	1 (1.4)	0.570
Sustained ventricular tachycardia, n (%)	15 (8.3)	12 (11)	3 (4.3)	0.121
Ventricular fibrillation, n (%)	1 (0.6)	1 (0.9)	0	0.426
Prior HF hospitalization, n (%)	45 (25)	25 (23)	20 (29)	0.359
Hemodynamic parameters
Systolic blood pressure, mmHg	122±20	124±21	120±17	0.169
Diastolic blood pressure, mmHg	69±12	70±11	69±12	0.912
Laboratory parameters
hs-cTnT, ng/mL	0.0373 [0.0214–0.0593]	0.0283 [0.0155–0.0445]	0.0485 [0.0352–0.0712]	0.004
BNP, pg/mL	220 [100–428]	188 [77–429]	245 [133–415]	0.778
Albumin, g/dL	3.8±0.6	3.8±0.6	3.8±0.6	0.918
Calcium, mg/dL	8.9±0.6	8.8±0.6	9.0±0.4	0.095
Corrected calcium, mg/dL	9.1±0.7	8.9±1.5	9.1±1.3	0.365
Hemoglobin, g/dL	12.9±1.9	12.6±2.1	13.0±1.9	0.281
Serum sodium, mEq/L	140±3	140±3	139±3	0.253
Creatinine, mg/dL	1.0±0.8	1.2±1.1	1.0±0.3	0.568
eGFR, mL/min/1.73 m2	55±19	55±21	54±15	0.347
CRP, mg/mL	0.10 [0.03–0.37]	0.11 [0.04–0.35]	0.09 [0.03–0.44]	0.835
ECG parameters
Heart rate, beats/min	67±13	70±17	66±13	0.244
PR duration, ms	195±41	186±37	212±41	<0.001
Prolonged PR interval, n (%)	53 (29)	25 (23)	28 (40)	0.001
QRS duration, ms	109±27	106±24	115±25	0.044
Wide QRS, n (%)	53 (29)	22 (20)	31 (44)	<0.001
CLBBB, n (%)	14 (7.7)	9 (8.1)	5 (7.1)	0.813
CRBBB, n (%)	24 (13)	9 (8.1)	15 (21)	0.010
IVCD, n (%)	15 (8.3)	4 (3.6)	11 (16)	0.004
QTc duration, ms	451±28	446±27	459±26	<0.001
Low QRS voltage in limb leads, n (%)	22 (12)	7 (6.3)	15 (21)	0.002
Poor R-wave progression in precordial leads, n (%)	27 (15)	12 (11)	15 (21)	0.051
Right axis deviation, n (%)	5 (2.8)	1 (0.9)	4 (5.7)	0.054
Left axis deviation, n (%)	58 (32)	30 (27)	28 (40)	0.069
Echocardiographic parameters
LV ejection fraction, %	55±12	56±12	53±10	0.553
LV end-diastolic diameter, mm	45±8	44±8	43±6	0.105
LV end-systolic diameter, mm	31±9	30±10	31±7	0.829
Intraventricular septal thickness, mm	14±3	13±3	15±2	<0.001
LV posterior wall thickness, mm	13±3	12±2	15±3	<0.001
Asymmetric septal hypertrophy, n (%)	12 (6.6)	10 (9.0)	2 (2.9)	0.105
Concentric hypertrophy, n (%)	125 (69)	60 (54)	65 (93)	<0.001
LV mass index, g/m2	151±46	132±39	174±40	0.090
LA diameter, mm	40±7	40±9	41±7	0.568
E-wave velocity, cm/s	71±25	69±26	75±24	0.192
A-wave velocity, cm/s	77±31	81±30	64±30	0.024
E/A ratio	1.2±1.5	1.1±1.6	1.5±1.2	0.391
E-wave deceleration time, ms	211±80	221±83	185±66	0.002
Restrictive LV filling pattern, n (%)	60 (33)	27 (24)	33 (47)	0.002
e’-wave velocity, cm/s	4.3±1.6	4.4±1.6	4.1±1.4	0.367
E/e’ ratio	18.2±7.4	17.4±7.7	19.7±6.7	0.097
Pericardial effusion, n (%)	51 (28)	25 (23)	26 (37)	0.031
Medications at baseline, n (%)
β-blocker	87 (48)	63 (57)	24 (34)	0.003
ACEI or ARB	93 (51)	60 (54)	33 (47)	0.365
Aldosterone antagonist	41 (23)	24 (22)	17 (24)	0.677
Diuretic	87 (48)	44 (40)	43 (61)	0.004
Anticoagulant	53 (29)	36 (32)	17 (24)	0.241
Statin	63 (35)	43 (39)	20 (29)	0.162

ACEI, angiotensin-converting enzyme inhibitor; ARB, angiotensin-receptor blocker; BNP, B-type natriuretic peptide; CLBBB, complete left bundle branch block; CRBBB, complete right bundle branch block; CRP, C-reactive protein; eGFR, estimated glomerular filtration rate; HF, heart failure; hs-cTnT, high-sensitivity cardiac troponin T; ICD, implantable cardioverter defibrillator; IVCD, interventricular conduction delay; LA, left atrial; LV, left ventricular; NYHA, New York Heart Association.

Figure 2.

Clinical diagnoses of patients in the ^{99 m}Tc-PYP negative group. AL, acquired monoclonal immunoglobulin light chain; ATTRm, mutant transthyretin amyloidosis.

In the ^{99 m}Tc-PYP positive group, 65 patients underwent tissue biopsy, of whom 55 (85%) had TTR amyloid deposition. Among them, 32 patients underwent EMB and TTR amyloid deposition in the heart was confirmed in all cases. DNA analysis was performed for 55 patients in the ^{99 m}Tc-PYP-positive group (79%); 46 patients did not have a TTR mutation (ATTRwt) and 9 patients had a TTR mutation (Val30Met [p.V50M] mutation: 7, Gly47Val [p.G67V] mutation: 1, Ala25Thr [p.A45T] mutation: 1). Collectively, we diagnosed 55 histologically proven cases of TTR-CA, comprising 46 ATTRwt, 8 ATTRm, and 1 without DNA analysis. One patient had a TTR mutation without proven TTR by tissue biopsy.

Factors Predictive of ^{99 m}Tc-PYP Positivity

To identify predictors of ^{99 m}Tc-PYP positivity, we performed univariate analyses. Among the laboratory parameters, only hs-cTnT was significantly associated with ^{99 m}Tc-PYP positivity (odds ratio [OR], 14.20; 95% confidence interval [CI], 4.46–44.86; P<0.001). Regarding the ECG parameters, wide QRS, complete right bundle branch block, intraventricular conduction delay, and low QRS voltage in the limb leads were significantly associated with ^{99 m}Tc-PYP positivity. To select an ECG parameter strongly related with ^{99 m}Tc-PYP positivity, we performed stepwise multiple logistic regression, which revealed that wide QRS remained a significant predictor of ^{99 m}Tc-PYP positivity (OR, 3.35; 95% CI, 1.69–6.63; P=0.001). Among the echocardiographic parameters, LV wall thickness, LV mass index, E-wave deceleration time, A-wave velocity, restrictive LV filling pattern, E/e′ ratio, and pericardial effusion were significantly associated with ^{99 m}Tc-PYP positivity. Stepwise multiple logistic regression showed that LV posterior wall thickness remained a significant predictor of ^{99 m}Tc-PYP positivity (OR, 2.03; 95% CI, 1.64–2.51; P<0.001) (Table 2). There was a strong correlation between LV posterior wall thickness and intraventricular septal thickness (Pearson correlation r=0.71). Intraventricular septal thickness was strongly associated with asymmetric septal hypertrophy, which is a typical finding of hypertrophic cardiomyopathy, but trended to be less likely in the ^{99 m}Tc-PYP positive group than in the ^{99 m}Tc-PYP negative group (2.9% vs. 9.0%, P=0.105). Therefore, we used LV posterior thickness rather than intraventricular septal thickness in the model.

Table 2. Univariate and Multivariate Analyses of ^{99 m}Tc-PYP Positivity

	Univariable analysis
	OR	95% CI	P value
Age, per 1 year increment	1.05	0.99–1.10	0.088
Male sex	2.92	1.42–3.45	0.004
NYHA class ≥II	1.69	0.83–5.12	0.148
Body mass index, per 1 kg/m2 increment	1.08	0.98–1.18	0.130
Hypertension	0.57	0.31–1.05	0.071
Diabetes mellitus	0.85	0.47–1.85	0.846
Dyslipidemia	0.61	0.32–1.17	0.140
Prior HF hospitalization	1.34	0.70–2.73	0.360
Atrial fibrillation	0.96	0.51–1.81	0.907
Systolic blood pressure, per 1 mmHg increment	0.99	0.97–1.01	0.172
Diastolic blood pressure, per 1 mmHg increment	1.00	0.98–1.03	0.912
Laboratory parameters
Log (hs-cTnT), per 1 ng/mL increment	14.20	4.46–44.86	<0.001
Log (BNP), per 1 pg/mL increment	1.74	0.90–3.37	0.101
Albumin, per 1 g/dL increment	0.97	0.59–1.61	0.915
Calcium, per 1 mg/dL increment	1.76	0.90–3.43	0.176
Corrected calcium, per 1 mg/dL increment	1.13	0.86–1.48	0.379
Hemoglobin, per 1 g/dL increment	1.11	0.95–1.29	0.179
Serum sodium, per 1 mEq/L increment	0.94	0.83–1.05	0.253
Creatinine, per 1 mg/dL increment	0.78	0.48–1.26	0.303
eGFR, per 1 mL/min/1.73 m2 increment	0.99	0.98–1.01	0.790
Log (CRP), per 1 mg/m increment	0.99	0.64–1.53	0.964
ECG parameters	Univariable analysis			Multivariable analysis of electrocardiographic parameters
	OR	95% CI	P value	OR	95% CI	P value
Heart rate, per 1beat/min increment	0.98	0.96–1.00	0.099
Wide QRS	3.22	1.66–6.24	0.001	3.35	1.69–6.63	0.001
CLBBB	0.87	0.28–2.72	0.813
CRBBB	3.09	1.27–7.52	0.013		VIF
IVCD	4.99	1.52–16.36	0.008		VIF
Low QRS voltages in limb leads	4.05	1.56–10.53	0.004	4.33	1.61–11.60	0.004
Poor R-wave progression in the precordial leads	2.25	0.98–5.15	0.055
Right axis deviation	6.67	0.73–60.92	0.093
Left axis deviation	1.80	0.95–3.40	0.070
Echocardiographic parameters	Univariable analysis			Multivariable analysis of electrocardiographic parameters
	OR	95% CI	P value	OR	95% CI	P value
LV ejection fraction, per 10% decrement	1.24	0.95–1.61	0.114
LV end-diastolic diameter, per 1 mm increment	0.74	0.48–1.15	0.178
LV end-systolic diameter, per 1 mm increment	0.77	0.51–1.16	0.207
IVS, per 1 mm increment	1.50	1.30–1.73	<0.001		VIF
LVPWT, per 1 mm increment	1.91	1.58–2.31	<0.001	2.03	1.64–2.51	<0.001
Concentric hypertrophy	11.05	4.13–29.54	<0.001		VIF
LV mass index, per 10 g/m2 increment	1.30	1.18–1.43	<0.001		Not selected
LA diameter, per 1 mm increment	1.01	0.97–1.05	0.662
E-wave velocity, per 10 cm/s increment	1.09	0.97–1.23	0.152
A-wave velocity, per 10 cm/s decrement	1.22	1.06–1.39	0.003		VIF
E-wave deceleration time, per 10 ms decrement	1.06	1.02–1.11	0.003		VIF
Restrictive LV filling pattern	2.75	1.45–5.20	0.002		Not selected
e’-wave velocity, per 1 cm/s decrement	1.14	0.93–1.40	0.211
E/e’ ratio, per 1 increment	1.04	1.00–1.09	0.046		Not selected
Pericardial effusion	2.06	1.06–3.98	0.032		Not selected

CI, confidence interval; IVS, intraventricular septal thickness; LVPWT, LV posterior wall thickness; OR, odds ratio; VIF, variance inflation factor. Other abbreviations as in Table 1.

ROC curve analysis showed the best hs-cTnT cutoff value was 0.0308ng/mL. The area under the ROC curve (AUC) was 0.730 (95% CI, 0.658–0.802; P<0.001) (Figure 3A). At this cutoff value, the sensitivity and specificity for predicting ^{99 m}Tc-PYP positivity were 80% and 59%, respectively. ROC curve analysis showed that the best LV posterior wall thickness cutoff value was 13.6 mm (AUC, 0.859; 95% CI, 0.803–0.915; P<0.001) with 70% sensitivity and 87% specificity (Figure 3B).

Figure 3.

Receiver-operator characteristic curve analysis of hs-cTnT (A) and LV posterior wall thickness (B) for predicting ^{99 m}Tc-PYP positivity. AUC, area under the curve; CI, confidence interval; hs-cTnT, high-sensitivity cardiac troponin T; LV, left ventricular; ^{99 m}Tc-PYP, ^{99 m}Tc-labeled pyrophosphate.

Kumamoto Criteria: Predictive Model for ^{99 m}Tc-PYP Positivity

Using hs-cTnT ≥0.0308 ng/mL, LV posterior wall thickness ≥13.6 mm, and wide QRS (QRS ≥120 ms), we created a new index to predict ^{99 m}Tc-PYP positivity, named the Kumamoto criteria. We calculated the index by adding 1 point for each factor. We divided the study patients into 4 groups by index point totals: 3-point group (n=23), 2-point group (n=46), 1-point group (n=57), and 0-point group (n=55). Figure 4 shows a typical case in the 3-point group. The ^{99 m}Tc-PYP positive rate increased by a factor of 4.57 (95% CI, 2.92–7.15) for each 1-point increase (P<0.001). Most patients in the 0-point group (87%) had negative results and most of the patients in the 3-point group (96%) had positive ^{99 m}Tc-PYP scintigraphy results (Figure 5). Only 1 patient with 3 points according to the Kumamoto criteria had a negative ^{99 m}Tc-PYP scintigraphy result; this patient had AL amyloidosis confirmed by EMB. The AUC of the index was 0.822 (95% CI, 0.756–0.888; P<0.001).

Figure 4.

Representative patient in the 3-point group shows a wide QRS (162 ms), thick left ventricular (LV) posterior wall (19.2 mm), and high hs-cTnT level (0.0632 ng/mL), ^{99 m}Tc-PYP scintigraphy showed moderate cardiac uptake on planar imaging, but computed tomography fusion imaging clearly visualized uptake in the myocardium and not in the cardiac blood pool. hs-cTnT, high-sensitivity cardiac troponin T; ^{99 m}Tc-PYP, ^{99 m}Tc-labeled pyrophosphate.

Figure 5.

Predictive model for ^{99 m}Tc-PYP scintigraphy. We developed an index for predicting ^{99 m}Tc-PYP positivity that adds 1 point for each of the following 3 variables: wide QRS (≥120 ms), thick LV posterior wall (≥13.6 mm), and high hs-cTnT levels (≥0.0308 ng/mL). The proportion of patients with ^{99 m}Tc-PYP positivity increased as the number of points increased. ^{99 m}Tc-PYP, ^{99 m}Tc-labeled pyrophosphate.

Discussion

The major finding of this study was that a combination of minimally invasive biochemical (hs-cTnT levels), physiological (wide QRS), and structural (LV posterior wall thickness) parameters can help clinicians stratify elderly patients with suspected TTR-CA and guide decisions about management strategies. This is the first study to highlight the ability of a combination of commonly examined parameters to raise the pretest probability of ^{99 m}Tc-PYP positivity.

Importance of Diagnosing TTR-CA in Elderly Patients With HF

TTR-CA was considered a rare disease, but recent studies have revealed a high prevalence of TTR-CA in both patients with HFpEF and LV hypertrophy³ and elderly patients.⁴ The prevalence of TTR-CA will continue to increase because of the aging of populations; therefore, TTR-CA has been receiving increased attention. Recent investigations of the clinical characteristics of ATTRwt showed the median age at diagnosis was high, ranging from 71.8 to 78.6 years.^21–23 The median age of TTR-CA patients in the Transthyretin Amyloidosis Cardiomyopathy Clinical Trial was 74 years.²⁴ Thus, we enrolled patients aged ≥70 years in this study.

Previously, TTR-CA had a bad prognosis without effective therapy.^25,26 A recent study, however, showed that a TTR stabilizer, tafamidis, is associated with reductions in all-cause death, cardiovascular-related hospitalizations, and in the decline in functional capacity and quality of life.²⁴ Therefore, it has become more important to diagnose TTR-CA in order to select appropriate therapeutic strategies.

Diagnostic Approach to TTR-CA Using ^{99 m}Tc-PYP Scintigraphy

There are many approaches to diagnosing TTR-CA. Recently, several studies showed that bone scintigraphy has excellent diagnostic accuracy.^6,9,27 According to Gilmore’s diagnostic algorithm for patients with suspected CA, patients with >grade 2 positivity on ^{99 m}Tc-PYP scintigraphy without monoclonal gammopathy can be diagnosed with TTR-CA without EMB.⁷ Therefore, it is important to suspect CA in patients with cardiac hypertrophy and actively perform ^{99 m}Tc-PYP scintigraphy to avoid underdiagnosis of CA.

Predictive Impact of Our Index for ^{99 m}Tc-PYP Positivity

The aim of our study was to evaluate predictive factors related to ^{99 m}Tc-PYP positivity and raise the pretest probability for ^{99 m}Tc-PYP scintigraphy in patients with suspected CA. Among findings from minimally invasive examinations, we selected a strongly significant factor from each modality: wide QRS (≥120 ms) from ECG, thick LV posterior wall (≥13.6 mm) from echocardiography, and high hs-cTnT (≥0.0308 ng/mL) from laboratory testing. In a further analysis, we compared the characteristics of patients with ^{99 m}Tc-PYP scores 0 and 1, which comprised the ^{99 m}Tc-PYP negative group. There were, however, no significant differences in hs-cTnT levels (P=0.160), QRS duration (P=0.978), and LV posterior wall thickness (P=0.178) between patients with visual ^{99 m}Tc-PYP scores 0 and 1.

These 3 factors are suspicious findings for CA. LV wall thickness is a fundamental characteristic of CA. Wide QRS is a manifestation of intraventricular or interventricular conduction delay or block. In fact, in patients with ATTRwt, 32% (33/108) in a large European cohort²¹ and 35% (17/49) in a Japanese nationwide survey²³ had bundle branch block; these findings are similar to the 29% (20/70) with bundle branch block in the ^{99 m}Tc-PYP positive group in this study. In addition, we previously showed that high levels of hs-cTnT enhanced the differentiation of CA from cardiac hypertrophy (optimal cutoff value 0.0312 ng/mL; sensitivity, 74%; specificity, 79%).⁸

We developed an index for predicting ^{99 m}Tc-PYP positivity by adding 1 point for each of the 3 factors. Patients with more points had a higher rate of being ^{99 m}Tc-PYP positive. Of note, patients in the 0-point group were rarely ^{99 m}Tc-PYP positive and almost all patients in the 3-point group were ^{99 m}Tc-PYP positive. Based on these findings, we made a recommendation on patient selection for ^{99 m}Tc-PYP scintigraphy (Figure 6). For patients with 0 or 1 point according to the Kumamoto criteria, consider other diagnoses and only perform ^{99 m}Tc-PYP scintigraphy if there are other suspicious findings on ECG and echocardiography or a history of carpal tunnel syndrome, which is frequently observed in patients with ATTRwt (46%).²⁸ Of note, among the 7 patients who were ^{99 m}Tc-PYP positive in the 0-point group, 3 had ATTRm. Therefore, when a patient already has TTR amyloidosis with a confirmed mutation based on DNA analysis, ^{99 m}Tc-PYP scintigraphy is useful for verifying cardiac involvement. We recommend performing ^{99 m}Tc-PYP scintigraphy in patients with ≥2 points in the criteria. In particular, patients with 3 points had a high pretest probability; therefore, even when ^{99 m}Tc-PYP scintigraphy results are negative, consider AL amyloidosis, which is associated with a low prevalence of ^{99 m}Tc-PYP scintigraphy positivity (27%).⁷ In our study, among the 23 patients with 3 points according to the criteria, 22 were ^{99 m}Tc-PYP positive and 1 had AL amyloidosis.

Figure 6.

New diagnostic strategy for TTR-CA using ^{99 m}Tc-PYP scintigraphy. CA, cardiac amyloidosis; hs-cTnT, high-sensitivity cardiac troponin T; LV, left ventricular; ^{99 m}Tc-PYP, ^{99 m}Tc-labeled pyrophosphate; TTR, transthyretin.

Study Limitations

First, this study had a relatively small number of patients and was performed at a single center. Validation using a similar cohort would be useful to support our results, but it is not possible because there are no similar cohorts. This is the first cohort study consisting of elderly patients who underwent ^{99 m}Tc-PYP scintigraphy for suspected CA, which is a novel and creative feature of our study. Therefore, despite the relatively small number of subjects, we believe that our results have value. Further prospective studies with more patients are needed to validate our results. Although we used a standardized protocol and ^{99 m}Tc-PYP scintigraphy interpretation was performed by the same independent operators, there is the possibility of referral bias. Future multicenter studies with more patients are needed to confirm the present results. Second, in this study, myocardial biopsy was performed in only 53 (29%) patients. Histopathological confirmation of amyloid deposition in the heart and DNA analysis are required for definitive diagnosis of CA. Third, we did not evaluate some indicators of CA. Relative apical sparing on echocardiography is a remarkable characteristic of CA (sensitivity 93% and specificity 82% in differentiating CA from LV hypertrophy).²⁹ However, we did not evaluate it because 2D speckle-tracking echocardiography was not preformed routinely in all patients with cardiac hypertrophy in Kumamoto University Hospital. In addition, we did not routinely evaluate RV free wall thickness, which is relevant to TTR-related amyloidosis.³⁰ These useful factors might raise the pretest probability of ^{99 m}Tc-PYP scintigraphy. Finally, the results of the stepwise selection process are potentially biased as a result of overfitting the derivation data set.

Conclusions

The combination of hs-cTnT, wide QRS, and LV posterior wall thickness can raise the pretest probability of ^{99 m}Tc-PYP scintigraphy using a novel index that can assist clinicians in determining the management strategies for patients with suspected CA.

Disclosures

The authors report no relationships that could be construed as a conflict of interest.

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