Natriuretic peptides have been used as diagnostic markers of heart failure in humans and dogs.1–3 C-terminal ANP consists of 28 amino acids and is produced by and released from the atrial myocardium in response to wall stretching in both humans and dogs.3–5 In addition, it plays a compensatory role in cardiorenal homeostasis, such as in vasodilatation, natriuresis, and inhibition of the renin-angiotensin-aldosterone system in humans.3 Quantification of natriuretic peptides, including ANP and BNP, has been used clinically in dogs for the diagnosis of heart disease.1,2 However, previous studies6,7 in human patients and experimental studies8,9 of heart disease in dogs have reported differential regulation of secretory mechanisms for ANP and BNP. In human patients with heart failure, the plasma ANP concentration was significantly correlated with values for pulmonary capillary wedge pressure, but the plasma BNP concentration was not.6 Also, we previously reported9 that chronic pressure overload in dogs with experimentally induced compensated aortic stenosis produced a stepwise increase in plasma N-terminal proBNP concentrations but not in plasma ANP concentrations over 6 months.
In humans and dogs, circulating ANP concentration can be used to predict the hemodynamic abnormality, severity, and prognosis for patients with chronic heart disease.3,10,11 An elevated ANP concentration has been described in humans with heart disease, including acute myocardial infarction and dilated cardiomyopathy.3,12,13 In dogs, ANP concentration is significantly related to pulmonary capillary wedge pressure and severity of mitral valve regurgitation.14 In 1 report,10 high plasma ANP concentration (> 92 pg/mL) was related to poor survival time in dogs with heart disease, including dilated cardiomyopathy and mitral valve regurgitation, suggesting that plasma ANP concentration is a potential noninvasive predictor of survival in dogs affected with these conditions. Thus, measuring plasma ANP concentration is informative for the diagnosis of chronic heart disease in clinical settings. However, plasma ANP concentrations do not differ between dogs with compensated heart disease and clinically normal dogs.14,15 Thus, the detailed clinical implications of plasma ANP concentrations in dogs remain unclear. Furthermore, the reference range of plasma ANP concentrations in dogs is unknown. The objective of the study reported here was to investigate the diagnostic utility of measurement of plasma ANP concentration in dogs with spontaneous heart disease. We investigated whether plasma ANP concentration could be used for the diagnosis of heart disease in dogs and to assess disease severity in affected dogs, and we determined a reference range of plasma ANP concentration for healthy dogs.
Materials and Methods
Dogs—The study population consisted of 115 dogs: 37 healthy dogs and 78 dogs with heart disease. All dogs were examined between February 2006 and October 2009 at the Kitasato University Veterinary Teaching Hospital and Kanie Animal Clinic. Healthy dogs were recruited from veterinary students and also included healthy dogs in the university laboratory. These dogs were determined to be healthy on the basis of results of physical examination, ECG, thoracic radiography, and echocardiography. All dogs underwent physical examination, echocardiography, thoracic radiography, and blood sampling, all of which were performed without sedation in a quiet examination room.
Inclusion criteria for the study for dogs with heart disease were confirmation of the diagnosis by echocardiography and not currently receiving treatment for cardiovascular disease. The diagnosis of heart disease was made on the basis of results of physical examination, ECG, plasma biochemical analysis, thoracic radiography, and echocardiography. All owners were asked detailed questions on whether dogs had received previous treatment for cardiovascular disease. In dogs with suspected decompensated heart failure (eg, dyspnea and cyanosis), all examination and blood sampling were performed rapidly to obtain a diagnosis and to distinguish cardiac from pulmonary disease. These dogs received supplemental oxygen via face mask. Congestive heart failure was diagnosed on the basis of radiographic evidence of caudodorsally distributed interstitial to alveolar pulmonary infiltrates and echocardiographic evidence of cardiac disease. Immediately upon obtaining a diagnosis, treatment was instituted for these patients.
Exclusion criteria for the study were concurrent systemic illness other than cardiovascular disease, such as pulmonary, endocrine, renal, hepatic, or inflammatory disease, and previous chronic drug treatment for cardiac disease. After all examinations were completed, if necessary, dogs received immediate medical treatment for heart disease. The study dogs were divided into a healthy group and 4 heart disease groups according to plasma ANP concentration: ANP-1 (< 50 pg/mL), ANP-2 (50 to 100 pg/mL), ANP-3 (101 to 200 pg/mL), and ANP-4 (> 200 pg/mL).
The study followed the Guidelines for Institutional Laboratory Animal Care and Use of the School of Veterinary Medicine, Kitasato University, Japan. Owners provided informed consent before their dogs participated in the study.
Thoracic radiography and echocardiography—Cardiothoracic ratio and VHS were evaluated by use of thoracic radiography according to the method described previously.16,17 Transthoracic echocardiography was performed by 2 experienced echocardiographers (YH and SY) using an ultrasonographic unit with a 7.5- to 12-MHz probe. Diagnosis of mitral valve disease, patent ductus arteriosus, and ventricular septal defect was made on the basis of echocardiographic detection of morphological abnormality and color flow Doppler echocardiographic evidence of abnormal flow. Mitral valve disease was diagnosed by use of color flow Doppler echocardiographic evidence of the mitral valve regurgitation. Similarly, patent ductus arteriosus was diagnosed with evidence of the vascular shunt, which revealed left-to-right shunt in the main pulmonary artery. Ventricular septal defect was diagnosed with evidence of the ventricular shunting flow and septal defect. A diagnosis of dilated cardiomyopathy was made on the basis of echocardiographic detection of eccentric left ventricular hypertrophy and low fractional shortening (< 25%) with 2-D M-mode echocardiography of the right parasternal short-axis view.
The LA:Ao ratio was measured from the right parasternal short-axis view. M-mode echocardiography was performed from the right parasternal short-axis view, and fractional shortening and RWT were calculated. Fractional shortening was calculated as ([left ventricular end-diastolic internal dimensions – left ventricular end-systolic internal dimensions]/left ventricular end-diastolic internal dimensions) × 100. Relative wall thickness was calculated as (end-diastolic intraventricular septum thickness + end-diastolic left ventricular posterior wall thickness)/left ventricular end-diastolic internal dimensions. In the left parasternal long-axis view, pulsed Doppler echocardiography was used to measure the transmitral flow velocity with the sample volume, which is a gate to receive and read an echo wave, positioned at the tip of the mitral valve leaflets. The mitral early diastolic flow (E wave) and late diastolic flow (A wave) velocities were measured, and the E:A ratio was calculated. Twelve dogs could not be subjected to detailed echocardiographic measurements such as M-mode and mitral valve inflow because of excitement, panting, or cardiac emergency (healthy group [n = 3], ANP-2 [1], ANP-3 [4], and ANP-4 [4]), but the diagnosis could be obtained from results of B-mode with color flow Doppler echocardiography, physical examination, plasma biochemical analysis, and thoracic radiographic examination performed prior to any treatment.
ANP measurement—Blood samples were collected from the cephalic vein at initial examination for the measurement of plasma C-terminal ANP concentrations in all dogs. The blood samples were collected into tubes that contained aprotinin and then centrifuged at 3,000 rpm for 10 minutes at 4°C. Plasma samples were stored at −70°C until analysis. The plasma ANP concentration was determined by chemiluminescence enzyme immunoassay for human α-ANP.a Precision data for ANP assay have been reported previously.9 For the purposes of statistical analysis, plasma concentrations below the detection limit of the ANP assay were assigned a value of 5 ng/mL.
Statistical analysis—All data are described as mean ± SD and median (range). The Kruskal-Wallis test was used to compare results of physical examinations, thoracic radiography, and echocardiography variables among all groups. A post hoc analysis was performed with the Dunn test. Spearman nonparametric correlation analysis was applied to compare plasma ANP concentrations with the hemodynamic or echocardiographic measurements. A value of P < 0.05 was considered significant. The relationship between each discrete variable of heart disease and plasma ANP concentration was further investigated with logistic regression analysis.
Receiver operating characteristic analyses were used to assess the predictive accuracy of plasma ANP concentration for detecting dogs with heart disease and to illustrate various cutoff values of plasma ANP concentrations.
Results
The study population of 115 dogs consisted of 23 (20%) mixed-breed dogs, 19 (16.5%) Beagles, 15 (13%) Shih Tzus, 10 (8.7%) Malteses, 8 (7.0%) Pomeranians, 7 (6.1%) Cavalier King Charles Spaniels, 6 (5.2%) Toy Poodles, 5 (4.3%) Chihuahuas, 4 (3.5%) Shibas, 3 (2.6%) Golden Retrievers, and 2 (1.7%) each of Miniature Dachshunds, Tibetan Terriers, and Yorkshire Terriers, and the remaining dogs represented 9 other breeds. The healthy group (n = 37) included 25 males and 12 females, ranging in age from 2 to 9 years and weighing 3.0 to 14.0 kg (6.6 to 30.8 lb). The heart disease group (n = 78) included 42 males and 36 females, ranging in age from 3 months to 18 years and weighing 1.2 to 35.2 kg (2.6 to 77.4 lb). A total of 58 of the 78 (74.4%) dogs were diagnosed with mitral valve disease, 10 (12.8%) with mitral and other valve disease, 7 (9.0%) with patent ductus arteriosus, 2 (2.6%) with dilated cardiomyopathy, and 1 (1.3%) with ventricular septal defect. According to the ISACHC classification,18 17 (21.8%) dogs were class I, 26 (33.3%) were class II, 14 (17.9%) were class IIIa, and 21 (26.9%) were class IIIb. Plasma ANP concentration was significantly increased in dogs with heart disease, compared with the healthy dogs (16.4 ± 7.8 pg/mL, 14.7 [6.5 to 44.9]; class I, 57.5 ± 43.7 pg/mL, 48 [12.1 to 170; P < 0.01]; class II, 86.9 ± 57.4 pg/mL, 61.5 [19.6 to 231; P < 0.001]; class IIIa, 174.3 ± 147.3 pg/mL, 130 [34.7 to 580; P < 0.001]; and class IIIb, 179.8 ± 87.8 pg/mL, 195 [54 to 351; P < 0.001]; Figure 1). In addition, plasma ANP concentration in ISACHC class IIIb dogs was significantly (P < 0.01) higher than that of class I dogs. However, plasma ANP concentrations overlapped notably between groups.
Comparison of plasma ANP concentration in healthy dogs (n = 37) and 4 groups of dogs (78) with heart disease grouped according to ISACHC classification. *P < 0.01 versus healthy dogs. †P < 0.001 versus healthy dogs. ‡P < 0.01 versus ISACHC class I.
Citation: Journal of the American Veterinary Medical Association 239, 8; 10.2460/javma.239.8.1077
To clarify the clinical implications of measurement of plasma ANP concentration, dogs with heart disease were divided into 4 ANP groups according to plasma ANP concentration: ANP-1 (n = 19 [24.4%]), ANP-2 (24 [30.8%]), ANP-3 (20 [25.6%]), and ANP-4 (15 [19.2%]). The physical examination and thoracic radiographic variables were compared among groups (Table 1). Dogs with heart disease were significantly older than the healthy group. Body weight was significantly lower in the ANP-2 (P < 0.01) and −4 (P < 0.05) groups, compared with the control group. Heart rate, CTR, and VHS increased concomitantly with the increase in plasma ANP concentrations. Heart rate was significantly higher in the ANP-2 (P < 0.05), −3 (P < 0.01), and −4 (P < 0.001) groups than in the healthy group. The CTR and VHS were significantly (P < 0.001) higher in the ANP-2, −3, and −4 groups than in the healthy group and significantly (P < 0.05) higher in the ANP-4 group than in the ANP-1 group. Plasma ANP concentration had a moderate positive correlation with CTR (r = 0.59; P < 0.001) but a weak positive correlation with VHS (r = 0.45; P < 0.001). The frequency of the severe murmur grade and ISACHC class significantly increased as the plasma ANP concentration increased (χ2 trend = 14.1 [P = 0.0002] and χ2 trend = 32.3 [P < 0.0001], respectively). Similarly, the frequency of the cough and pulmonary edema significantly increased as the plasma ANP concentration increased (χ2 trend = 36.9 [P < 0.0001] and χ2 trend = 15.6 [P < 0.0001], respectively; Table 2).
Comparison of physical examination and thoracic radiographic variables among healthy dogs (n = 37) and 4 groups of dogs (78) with heart disease grouped according to serum ANP concentration.
| Group | Healthy (n = 37) | ANP-1 (n = 19) | ANP-2 (n = 24) | ANP-3 (n = 20) | ANP-4 (n = 15) |
|---|---|---|---|---|---|
| Age (y) | 5.3 ± 2.5 | 9.8 ± 3.7c | 9.4 ± 4.6b | 11.8 ± 2.6c | 10.1 ± 4.1c |
| 5.5 (1–13.8) | 11 (0.2–14) | 10 (0.3–18) | 12 (6.3–16) | 11 (0.3–15) | |
| Body weight (kg) | 9.7 ± 2.7 | 7.7 ± 5.8 | 6.2 ± 4.4b | 8.0 ± 7.4 | 6.6 ± 4.5a |
| 10 (3–15.5) | 5.7 (2.2–23) | 4.6 (1.7–20.5) | 5.4 (2.3–35.2) | 5.6 (1.2–16) | |
| Body temperature (°C) | 39.0 ± 0.4 | 38.6 ± 0.5 | 38.4 ± 0.5 | 38.8 ± 1.7 | 38.4 ± 0.7 |
| 38.9 (37.4–39.8) | 38.6 (38–39.3) | 38.4 (37–39.2) | 38.2 (37.8–39) | 38.8 (37–39.1) | |
| Respiratory rate (/min) | 29.3 ± 7.7 | 45.2 ± 27.6 | 44.3 ± 20.3 | 56.0 ± 48.1a | 50.7 ± 13.8b |
| 30 (18–48) | 39 (18–120) | 40 (28–93) | 42 (20–180) | 48 (36–72) | |
| Heart rate (beats/min) | 101 ± 21 | 122 ± 29 | 137 ± 43a | 149 ± 32b | 160 ± 48c |
| 102 (61–141) | 120 (86–194) | 131 (76–207) | 134 (113–204) | 164 (113–254) | |
| CTR (%) | 47.7 ± 4.0 | 57.1 ± 8.5 | 63.3 ± 13c | 65.2 ± 8.4c | 74.7 ± 7.1*,c |
| 47.2 (39.3–63) | 55 (45–72.5) | 60 (43–88) | 65 (51.1–80.6) | 75.5 (64–84.4) | |
| VHS | 9.9 ± 0.6 | 10.6 ± 1.1 | 11.7 ± 1.5c | 11.4 ± 0.9c | 12.3 ± 1.3*,c |
| 10.2 (8.5–11.7) | 10.7 (8.5–12.8) | 11.8(8.5–15.6) | 11.4 (10–12.8) | 12.3 (9.9–14.2) |
Values are mean ± SD and median (range).
P < 0.05 versus ANP-1.
P < 0.05 versus healthy dogs.
P < 0.01 versus healthy dogs.
P < 0.001 versus healthy dogs.
Dogs with heart disease were grouped according to plasma ANP concentration: ANP-1 (< 50 pg/mL), ANP-2 (50 to 100 pg/mL), ANP-3 (101 to 200 pg/mL), and ANP-4 (> 200 pg/mL).
To convert kg to lb, multiply by 2.2.
Classification of the dogs in Table 1 according to sex, murmur grade, ISACHC class, and the presence or absence of a cough or pulmonary edema.
| Group | Healthy | ANP-1 | ANP-2 | ANP-3 | ANP-4 |
|---|---|---|---|---|---|
| Sex | |||||
| Male | 12 | 9 | 12 | 13 | 8 |
| Female | 25 | 10 | 12 | 7 | 7 |
| Murmur grade | |||||
| II/VI | — | 5 (26.3) | 1 (4.2) | 0 | 0 |
| III/VI | — | 11 (57.9) | 11 (45.8) | 7 (35.0) | 2 (13.3) |
| IV/VI | — | 3 (15.8) | 9 (37.5) | 13 (65.0) | 11 (73.3) |
| V/VI | — | 0 | 3 (12.5) | 0 | 2 (13.3) |
| ISACHC class | |||||
| I | 0 | 9 (47.4) | 6 (25.0) | 2 (10.0) | 0 |
| II | 0 | 9 (47.4) | 8 (33.3) | 8 (40.0) | 1 (6.7) |
| IIIa | 0 | 1 (5.3) | 6(25.0) | 2 (10.0) | 5 (33.3) |
| IIIb | 0 | 0 | 4(16.7) | 8 (40.0) | 9 (60.0) |
| Cough | |||||
| Yes | 1 (2.8) | 4 (21.1) | 14 (58.3) | 12 (60.0) | 13 (86.7) |
| No | 36 (97.2) | 15 (78.9) | 10 (41.7) | 8 (40.0) | 2 (13.3) |
| Pulmonary edema | |||||
| Yes | 0 (0) | 0 (0) | 7 (29.2) | 7 (35.0) | 8 (53.3) |
| No | 15 (100) | 15 (100) | 17 (70.8) | 13 (65.0) | 7 (46.7) |
All data are described as the actual value (%).
— = Not applicable.
See Table 1 for remainder of key.
Fractional shortening was significantly higher in the ANP-1 (P < 0.05), −2 (P < 0.01), −3 (P < 0.001), and −4 (P < 0.05) groups than in the healthy group (Table 3). The RWT gradually decreased concomitantly with an increase of plasma ANP concentrations and was significantly (P < 0.05) lower in the ANP-4 group than in the healthy group. The LA:Ao ratio, E wave velocity, and E:A ratio increased concomitantly with an increase of plasma ANP concentrations. The LA:Ao ratio and E wave velocity were significantly (P < 0.001) higher in the ANP-2, −3, and −4 groups than in the healthy group. The A wave velocity was significantly higher in the ANP-2 (P < 0.01) and −3 (P < 0.001) groups than in the healthy group. The E:A ratio was significantly (P < 0.05) higher in the ANP-4 than in the healthy group and significantly (P < 0.05) higher in the ANP-4 than in the ANP-1 group.
Comparison of echocardiographic variables among the groups of dogs in Table 1.
| Group | Healthy (n = 34) | ANP-1 (n = 19) | ANP-2 (n = 23) | ANP-3 (n = 16) | ANP-4 (n = 11) |
|---|---|---|---|---|---|
| IVSd (mm) | 7.0 ± 1.4 | 6.6 ± 1.9 | 6.2 ± 1.5 | 6.8 ± 2.6 | 7.0 ± 2.5 |
| 7.3 (4.3–9.7) | 6.5 (4.1–11) | 6.2 (2.9–9.0) | 6.6 (3.4–15) | 7.6 (3.5–11) | |
| LVIDd (mm) | 30.0 ± 4.3 | 30.2 ± 8.5 | 32.7 ± 8.9 | 34.2 ± 10.2 | 35.1 ± 8.4 |
| 30.8 (19.9–36.8) | 31.3 (17.5–45.4) | 29.6 (16.8–52.3) | 29.5 (24.2–54) | 34 (24.9–52.2) | |
| LVPWd (mm) | 7.4 ± 1.5 | 7.0 ± 1.9 | 6.6 ± 1.6 | 6.7 ± 1.8 | 5.5 ± 1.6 |
| 7.2 (4.7–9.9) | 6.9 (4.6–11.3) | 6.5 (42.9–10) | 6.1 (4.7–11) | 5.8 (3.2–8.0) | |
| Fractional shortening (%) | 34.3 ± 5.5 | 43.1 ± 12.1a | 43.9 ± 10.2b | 45.9 ± 12.2c | 48.1 ± 12.1a |
| 34.5 (20.4–49.5) | 42.7 (19.5–62.4) | 44.2 (31.8–70.9) | 45.7 (8.7–62.1) | 45.5 (32–72.4) | |
| RWT | 0.49 ± 0.09 | 0.47 ± 0.14 | 0.41 ± 0.12 | 0.40 ± 0.06 | 0.36 ± 0.11a |
| 0.47 (0.32–0.67) | 0.46 (0.23–0.71) | 0.39 (0.28–0.76) | 0.4 (0.25–0.48) | 0.38 (0.22–0.56) | |
| LA:Ao ratio | 1.4 ± 0.2 | 1.6 ± 0.3 | 2.0 ± 0.5c | 2.0 ± 0.5c | 2.3 ± 0.6*,c |
| 1.3 (1.1–1.7) | 1.6 (1.1–2.7) | 1.8 (1.4–3.2) | 1.9 (1.0–2.9) | 2.2 (1.6–3.5) | |
| E wave velocity (cm/s) | 61.7 ± 10.9 | 75.9 ± 25.0 | 97.0 ± 28.2c | 109.5 ± 31.6c | 124.5 ± 34.5†,c |
| 59.2 (43.6–87.5) | 76.8 (29.7–120) | 94.7 (55.8–153) | 104 (67.4–168) | 127 (87.7–188.3) | |
| A wave velocity (cm/s) | 50.0 ± 8.6 | 61.6 ± 18.4 | 72.3 ± 19.2c | 73.8 ± 24.5b | 56.7 ± 23.4 |
| 49.2 (33.8–68.6) | 61.8 (28.9–104.8) | 69.8 (46.2–111.6) | 72.9 (40–133.5) | 57.5 (32.7–95.8) | |
| E:A ratio | 1.3 ± 0.3 | 1.3 ± 0.4 | 1.4 ± 0.5 | 1.7 ± 1.0 | 2.6 ± 1.2*,a |
| 1.2 (0.7–1.9) | 1.2 (0.6–2.4) | 1.3 (0.7–2.3) | 1.4 (0.8–4.2) | 2.1 (0.9–3.9) |
P, 0.01 versus ANP-1.
IVSd = End-diastolic intraventricular septum thickness. LVIDd = Left ventricular end-diastolic internal dimension. LVPWd = End-diastolic left ventricular posterior wall thickness.
See Table 1 for remainder of key.
Plasma ANP concentration had a moderate positive correlation with LA:Ao ratio (r = 0.58; P < 0.001), E wave velocity (r = 0.58; P < 0.001), and E:A ratio (r = 0.55; P < 0.001) but a weak positive correlation with heart rate (r = 0.44; P < 0.001) and fractional shortening (r = 0.32; P < 0.001). In contrast, plasma ANP concentration had a weak negative correlation with RWT (r = −0.34; P < 0.001).
Sensitivity and specificity for detecting dogs with severity of heart disease at relevant cutoff values were determined (Table 4). Use of plasma ANP concentration ≥ 25 pg/mL to identify dogs with heart disease (ISACHC class ≥ I) had a sensitivity of 91.0% and a specificity of 94.7%. Use of plasma ANP concentration ≥ 50 pg/mL to identify dogs with ISACHC class ≥ II had a sensitivity of 83.6% and specificity of 86.8%. Use of plasma ANP concentration ≥ 100 pg/mL to identify dogs with ISACHC class IIIb had a sensitivity of 81.0% and specificity of 81.1%. The area under the receiver operating characteristic curve for dogs with ISACHC class ≥ I, ≥ II, and IIIb was 0.97, 0.93, and 0.87, respectively (Figure 2).
Receiver operating characteristic curves displaying sensitivity and specificity of using plasma ANP concentration for distinguishing healthy dogs (n = 37) from dogs with heart disease (78). A—ISACHC class > I. B—ISACHC class > II. C—ISACHC class > IIIb.
Citation: Journal of the American Veterinary Medical Association 239, 8; 10.2460/javma.239.8.1077
Diagnostic performance of plasma ANP concentration for the detection of dogs with heart disease.
| Variable | ISACHC ≥ I | ISACHC ≥ II | ISACHC IIIb |
|---|---|---|---|
| Cutoff value (pg/mL) | 25 | 50 | 100 |
| AUC | 0.97 | 0.93 | 0.87 |
| 95% CI | 0.918–0.992 | 0.866–0.969 | 0.799–0.928 |
| Sensitivity (%) | 91.0 | 83.6 | 81.0 |
| Specificity (%) | 94.7 | 86.8 | 81.1 |
| False-positive rate (%) | 5.3 | 14.8 | 18.9 |
| False-negative rate (%) | 9.1 | 16.7 | 20 |
| PPV (%) | 97.3 | 86.4 | 48.6 |
| NPV (%) | 83.7 | 82.1 | 95.1 |
AUC = Area under the receiver operating characteristic curve. CI = Confidence interval. NPV = Negative predictive value. PPV = Positive predictive value.
Discussion
Results of the present study suggest that measurement of plasma ANP concentration may be a useful marker for predicting the severity of heart disease in dogs. Compared with healthy dogs, dogs with increased plasma ANP concentration had significant concomitant increases in heart rate, CTR, VHS, fractional shortening, LA:Ao ratio, and mitral early diastolic flow (E wave) velocity and a significant decrease in RWT. Use of plasma ANP concentration ≥ 25 pg/mL to identify dogs with heart disease (ISACHC class ≥ I) had a sensitivity of 91.0% and a specificity of 94.7%.
Atrial natriuretic peptide is one of the natriuretic peptides, consists of 28 amino acids, and is released from the atrium in response to wall stretching in both humans and dogs.4,5,19 In humans, the measurement of ANP concentration is useful for predicting the severity or prognosis of heart disease because patients with higher ANP concentrations have a poorer prognosis.3,11,20 Plasma ANP concentration has been reported1,14,15 to predict the severity of heart disease in several breeds of dog. Doberman Pinschers with occult dilated cardiomyopathy had significantly higher ANP concentrations than those of clinically normal dogs.3 Asano et al14 reported that plasma ANP concentration was significantly higher in dogs with decompensated heart failure (NYHA classification IV) than in clinically normal dogs. Similarly, Haggstrom et al15 reported that among Cavalier King Charles Spaniels with mitral valve regurgitation, plasma ANP concentration was significantly higher in dogs with congestive heart failure (NYHA III and IV) than in clinically normal dogs. However, plasma ANP concentrations did not differ significantly between dogs with compensated heart disease (NYHA I and II) and clinically normal dogs.14,15 Similarly, plasma ANP concentrations overlapped notably between groups in the present study. Thus, the detailed clinical implications of plasma ANP concentrations in dogs remain unclear. In the present study, plasma ANP concentrations increased concomitantly with increases in the CTR, VHS, fractional shortening, and E wave velocity in dogs with heart disease and a simultaneous decease in RWT. Of note, plasma ANP concentration showed a moderate positive correlation with CTR and E wave velocity. The murmur grade, ISACHC class, and presence of cough and pulmonary edema were significantly correlated with an increase in the plasma ANP concentration. Our results are consistent with the results of previous studies,1,14,15 which indicate that measurement of plasma ANP concentration may have the potential to predict the severity of disease in dogs with heart disease.
Atrial natriuretic peptide and BNP are useful as cardiac biomarkers and used widely in clinical settings to diagnose heart failure in humans3,6,11–13 and dogs.1,2,10,14 However, previous human studies6,21,22 have reported differential regulation of secretory mechanisms for ANP and BNP. Atrial natriuretic peptide is released in response to a hemodynamic abnormality related to atrial loading in patients with congestive heart failure, but BNP is not. Yoshimura et al6 reported that the plasma concentrations of ANP and BNP had a highly positive correlation with pulmonary capillary wedge pressure in patients with dilated cardiomyopathy in whom both atria and ventricles are dilated. However, in patients with mitral stenosis with predominantly atrial dilation, only plasma ANP concentrations had a highly significant correlation with pulmonary capillary wedge pressure.6 In addition, in human patients with left ventricular dysfunction, the only independent predictor of sudden death was plasma BNP concentration and the best independent predictor of heart failure death was plasma N-terminal ANP concentration.21,22 In dogs with acute cardiac volume overload, plasma ANP concentration was significantly correlated with pulmonary capillary wedge pressure, but plasma N-terminal pro-BNP concentration was not.23 In dogs, plasma ANP concentration correlates significantly with left atrial dilation and left ventricular enlargement.14,15 Similarly, left atrial enlargement had a predominant effect on plasma ANP concentration in Cavalier King Charles Spaniels with mitral valve regurgitation.15 These results suggest that atrial volume overload is a predominant factor stimulating the release of plasma ANP into blood. In the present study, increases in plasma ANP concentrations were correlated with an increase in the LA:Ao ratio and plasma ANP concentration showed a moderate positive correlation with the LA:Ao ratio. These results indicate that measurement of plasma ANP concentration may have the potential to predict atrial enlargement in dogs with heart disease.
In the present study, use of plasma ANP concentration > 25 pg/mL to identify dogs with the ISACHC class > I, regardless of heart disease severity, had high sensitivity and specificity (91.0% and 94.7%, respectively). Although the plasma ANP concentration of healthy dogs was 16.4 ± 7.8 pg/mL (range, 6.5 to 44.9 pg/mL), only 2 of 37 clinically normal dogs had concentrations exceeding the cutoff value (25 pg/mL). These results indicate that a plasma ANP concentration > 25 pg/mL may be useful to distinguish dogs with or without hemodynamic abnormality in the left atrium. In addition, use of a plasma ANP concentration > 100 pg/mL to identify dogs with the ISACHC class IIIb had moderate sensitivity and specificity (81.0% and 81.1%, respectively). This result indicates that a plasma ANP concentration > 100 pg/mL may be the cutoff for predicting dogs with decompensated heart failure.
The present study had several limitations. Several breeds of dogs with heart disease were enrolled; therefore, further studies are required to define the relationship between plasma ANP concentrations and heart disease for individual breeds. For our study population, although most patients had mitral regurgitation, other diseases such as congenital heart disease and cardiomyopathy were included. We could not exclude the possibility that individual heart diseases may lead to different responses in ANP. Several factors may affect plasma ANP concentrations in dogs, including systemic blood pressure, age, and renal function.24 Therefore, we need to interpret our results with caution. Our study was limited by its small sample size of dogs with ISACHC class IIIb (n = 21), and further large-sample studies will be required to identify the cutoff values for distinguishing dogs with heart failure.
ABBREVIATIONS
| ANP | Atrial natriuretic peptide |
| BNP | B-type natriuretic peptide |
| CTR | Cardiothoracic ratio |
| E:A | E-to-A wave |
| ISACHC | International Small Animal Cardiac Health Council |
| LA:Ao | Left atrial-to-aortic root diameter |
| NYHA | New York Heart Association |
| RWT | Relative wall thickness |
| VHS | Vertebral heart score |
Shionoria-ANP, Shionogi Co, Osaka, Japan.
References
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