cardiac natriuretic peptides and continuously monitored atrial pressures during chronic rapid pacing...

Cardiac natriuretic peptides and continuously monitored

atrial pressures during chronic rapid pacing in pigs

W . Q I , H . K J E K S H U S , R . K L I N G E , J . K . K J E K S H U S and C . H A L L

Institute for Surgical Research and Department of Cardiology, The National Hospital, The University of Oslo, Oslo, Norway

ABSTRACT

Changes in atrial natriuretic peptide (ANP), N-terminal proatrial natriuretic peptide and brain natriuretic

peptide (BNP) were evaluated in relation to continuously monitored atrial pressures in a pacing model

of heart failure. Pigs were subjected to rapid atrial pacing (225 beats min)1) for 3 weeks with

adjustments of pacing frequencies if the pigs showed overt signs of cardiac decompensation. Atrial

pressures were monitored by a telemetry system with the animals unsedated and freely moving. Left

atrial pressure responded stronger and more rapidly to the initiation of pacing and to alterations in the

rate of pacing than right atrial pressure. Plasma natriuretic peptide levels were measured by

radioimmunoassay and all increased during pacing with BNP exhibiting the largest relative increase

(2.9-fold increase relative to sham pigs). Multiple regression analysis with dummy variables was used

to evaluate the relative changes in natriuretic peptides and atrial pressures and the strongest

correlation was found between BNP and left atrial pressure with R 2 � 0.81. Termination of pacing

resulted in rapid normalization of ANP values in spite of persistent elevations in atrial pressures. This

may re¯ect an increased metabolism or an attenuated secretory response of ANP to atrial stretch

with established heart failure. In conclusion, 3 weeks of rapid pacing induced signi®cant increases in

atrial pressures and natriuretic peptide levels. All the natriuretic peptides correlated with atrial

pressures with BNP appearing as a more sensitive marker of cardiac ®lling pressures than ANP and

N-terminal proatrial natriuretic peptide.

Keywords atrial natriuretic peptide, atrial pressures, brain natriuretic peptide, correlation,

heart failure, N-terminal proatrial natriuretic peptide, rapid pacing, telemetry system.

Received 16 September 1999, accepted 21 February 2000

The cardiac hormones, atrial natriuretic peptide (ANP)

and brain natriuretic peptide (BNP), compose a dual

vasoactive natriuretic peptide system mediating natri-

uresis, diuresis and vasodilatation through the natri-

uretic peptide receptor-A (de Bold et al. 1981, Maack

et al. 1987, Chang et al. 1989, Saito et al. 1989, Yoshi-

mura et al. 1991). Both peptides are synthesized as

inactive precursors, which are cleaved to the mature

peptides and their respective N-terminal fragments.

The role of the N-terminal fragments has not been

clari®ed, but they circulate at higher plasma concen-

tration, and have a greater stability and a longer half-life

than the mature peptides (Sundsfjord et al. 1988,

Nelesen et al. 1992, Hall et al. 1995, Pemberton et al.

1998). The natriuretic peptides are metabolized partly

by clearance through the binding to natriuretic peptide

receptor-C, and partly by degradation by endopeptid-

ases (Rademaker et al. 1997). Natriuretic peptide plasma

concentration relates closely to atrial pressures and

signi®cant increases have been observed in patients

with congestive heart failure (CHF) (Rodeheffer et al.

1986, Mukoyama et al. 1990, Maeda et al. 1998).

N-terminal proANP (NT-proANP), which is co-

secreted with ANP, is currently used as diagnostic and

prognostic marker of CHF owing to its greater stability

and reliability of measurement compared with mature

ANP (Hall et al. 1994, 1995). A recent report by

Tsutamoto et al. (1997) suggests that BNP may be

better than ANP as a predictor of mortality in patients

with CHF. However, whether BNP may be a more

sensitive diagnostic marker of CHF is as yet unclear.

We therefore wanted to investigate the temporal

changes in ANP, NT-proANP and BNP during the

evolution of heart failure. We employed a porcine

model of rapid atrial pacing which we have previously

shown to exhibit haemodynamic and neurohormonal

Correspondence: Wei Qi, Institute for Internal Medicine, The National Hospital (Rikshospitalet), The University of Oslo, Sognsveien 20 Oslo,

Norway.

Acta Physiol Scand 2000, 169, 95±102

Ó 2000 Scandinavian Physiological Society 95

alterations similar to those of human CHF (Klinge et al.

1998). In the present study, we used an implantable

telemetry pressure system to continuously monitor left

and right atrial pressures in the same setting. The aim

was to relate the temporal changes in ANP, NT-

proANP and BNP, to the corresponding changes in left

and right atrial pressures as indices of cardiac preload

and stimulus of natriuretic peptide secretion.

MATERIALS AND METHODS

Animal preparation

Norwegian farm pigs (sus scrofa) were treated and

cared for in accordance with the `European Convention

for the Protection of Vertebrate Animals used for

Experimental and other Scienti®c Purposes' (Council of

Europe no. 123, Strasbourg 1985). The study protocol

was approved by the local laboratory animal science

specialist under the surveillance and registration of the

Norwegian Animal Research Authority.

All pigs were subjected to a left thoracotomy in the

third intercostal space and exposure of the heart

through a pericardiotomy. Prior to surgery they were

premedicated with ketamine 20 mg kg)1 i.m. (Parke-

Davis Scandinavia AB, Sweden), azaperon

3 mg kg)1 i.m. (StresnilÒ, Janssen-CilaG, Pharma,

Austria) and atropine sulphate 0.05 mg kg)1 i.m.

Anaesthesia was induced with pentobarbital

10 mg kg)1 i.v., and the pigs were ventilated with a

mixture of iso¯urane (ForeneÒ, Abbott Laboratories,

England) 1±2%, nitrous oxide 60% and oxygen 38±

39% using constant volume positive pressure ventila-

tion (Siemens servo 900B, Siemens, Sweden) adjusted

according to arterial blood gas determinations. Anal-

gesia was maintained during the procedure with mida-

zolam 5 mg mL)1 (DormicumÒ, F. Hoffmann-La

Roche AG, Switzerland) and fentanyl 500 g mL)1

(Antigen Pharmaceuticals Ltd, Ireland) infused at

2 mL h)1. In the paced pigs (n � 10; 7 male, 3 female)

weighing 28.2 (range 23±33 kg), a programmable

pacemaker (Pasys 8329, Medtronic, Minneapolis, MN)

was implanted in the upper left subcostal space with a

unipolar shielded electrode sutured to the left atrium. In

nine pigs, gel-tipped, ¯uid-®lled catheters were inserted

into the auricles of the right and left atria and secured in

place with a purse string suture. Bipolar ECG leads

were tunnelled subcutaneously »10 cm apart on the left

side of the thorax. The catheters and ECG-leads were

connected to a telemetry transmitter unit (TL11M3-

D70-PCP, Data Sciences International, USA) placed in

a subcutaneous pocket in the left thoracic ¯ank,

enabling continuous monitoring of atrial pressures and

ECG. For repeated blood sampling, a silicone catheter

was positioned into the superior vena cava through the

left external jugular vein. The catheter was brought

through the skin under a protective sheet in the dorsal

midline of the neck. It was ¯ushed with 0.9% saline and

®lled with 1000 IE of heparin every other day. Sham-

operated pigs (n � 7; 6 male, 1 female) weighing 30.2

(range 30±38) kg underwent the same procedure, but

did not receive a pacemaker or a telemetry unit.

Ampicillin (1.5 mg kg)1 i.m.) and buprenorphinum

(0.3 mg i.m. b.i.d.) were given to all pigs the ®rst three

postoperative days.

Experimental protocol

The pigs were allowed to recover for 6 to 10 days after

surgery. Then, atrial pacing at 225 beats min)1 was

started and continued for 21 days. The animals were

inspected clinically every day and rectal temperature

was recorded. If the temperature was above 40 °C, the

animal received cefalotin 1.0 g daily for 3±4 days. ECG

was monitored to ensure 1:1 conduction of the

programmed frequencies. If the animals showed signs

of intolerance to pacing, the pacing frequency was

temporarily adjusted downwards as advised by the

consulting veterinarian. Twenty-four hours after

termination of pacing, an invasive haemodynamic study

was undertaken and the animals were sacri®ced by

excision of heart.

Pressure data acquisition

Atrial pressures were monitored from 3 days before

initiation of pacing until 24 h after the cessation of

pacing. The pressure and ECG signals were transmitted

to two receivers (RLA 2000, Data Science International,

USA) mounted on the cage wall and fed into a personal

computer. The computer sampled mean systolic and

diastolic atrial pressures and heart rates over a period of

5 s every hour (Dataquest LabPRO, Version 3.01, Data

Science International, USA). Technically satisfactory

data were acquired from six of the nine pigs with

implanted telemetry units. Pressure and ECG data were

acquired while the animals were moving freely within

their cages. Signi®cant variations, in pressure

measurements were seen in the animals, mostly as

simultaneous variations in both left and right atrial

pressures relating to alterations in animal posture,

spontaneous ventilation and grunting. However, there

were also some artefacts observed as asynchronous,

more extreme variations, in pressure. To ®lter out such

artefacts, the moving median (�12 h) was calculated for

the systolic and diastolic pressures for each atrium and

individual values deviating more than 40 mmHg from

the moving median were eliminated. The median of the

remaining systolic and diastolic values for each

preceding 24-h period was calculated and subsequently

96 Ó 2000 Scandinavian Physiological Society

Natriuretic peptide and atrial pressure � W Qi et al. Acta Physiol Scand 2000, 169, 95±102

averaged to obtain the mean left and right atrial pres-

sure for each 24-h period.

Haemodynamic study 24 h postpacing

Twenty-four hours after cessation of pacing, the pigs

were anaesthetized once more omitting azaperon and

pentobarbital from the regimen to avoid their depres-

sive effects on the circulation. The right carotid artery

was exposed and a pigtail catheter was introduced for

measurements of mean arterial pressure (MAP) and left

ventricular end diastolic pressure (LVEDP). The right

internal jugular vein was exposed and a Swan±Ganz

catheter was introduced for measurements of central

venous pressure (CVP), pulmonary arterial pressure

(PAP) and pulmonary capillary wedge pressure

(PCWP). The catheters were connected to AE840

transducers (SensoNor, Horten, Norway). ECG and

pressure waveforms were recorded using a multi-

channel recorder (Gould ES 2000 CP, Gould, USA).

Following a stabilization period of 15 min after cathe-

terization, two pressure recordings were conducted

with an interval of 10 min and averaged. Cardiac output

was determined in triplicate by the thermodilution

technique through the Swan±Ganz catheter which was

connected to a SAT-2 cardiac output computer (Baxter

Healthcare Corp., Irvine CA, USA). During measure-

ment, the haemodynamic data were digitized and stored

on a personal computer for subsequent analysis

utilizing the CVSOFT analysis program (version 2.2,

Odessa Computer Systems, Calgary, Canada).

Immunoassay of natriuretic peptides

Blood samples were withdrawn in the morning of 3

subsequent days before pacing onset, at day 1, 7, 14, 21

on pacing, and 24 h after cessation of pacing. Whole

blood (50 mL) from the superior vena cava was

collected each time into prechilled EDTA vacutainers

for analysis of ANP, NT-proANP and BNP. Immedi-

ately after sampling, the tubes were placed on ice and

centrifuged at 4 °C before plasma aliquots were frozen

at )70 °C until analysis.

The plasma ANP (irANP 99±126) concentration

was measured directly in plasma by an IRMA-kit for

human ANP (Shionoria ANP, Shionogi & Co., Ltd).

The detection limit for ANP was 1.4 pmol L)1 and the

between- and within-assay coef®cients of variation were

6.0 and 4.8%, respectively. Recovery was 75.4%

(n � 10).

The plasma NT-proANP (irANP 1±98) concentra-

tion was measured in unextracted plasma according to

Sundsfjord et al. (1988). The assay utilizes a polyclonal

antibody from rabbits immunized with rat ANP (11±

37), showing 100% cross-reactivity with human ANP

(1±30) (Cat. no. 9129, Peninsula Laboratory, Belmont,

CA). The detection limit for NT-proANP was

185 pmol L)1 and the between- and within-assay

coef®cients of variation were 6.3 and 4.1%, respecti-

vely. Recovery was 85.0% (n � 10).

The plasma BNP concentration was measured by an

RIA-kit for porcine BNP (Cat. no. 9096, Peninsula

Laboratories, Belmont, CA) after C18 Sep-Pak cartridge

extraction. The detection limit for BNP was

1.44 pmol L)1 and the between- and within-assay

coef®cients of variation were 9.0 and 5.5%, respect-

ively. Recovery was 48.0% (n � 10).

Calculations and statistical analysis

Continuous variables are presented as mean � 95%

con®dence interval, unless otherwise noted. A two-

tailed unpaired t-test was used to compare between

pacing and sham groups except for the natriuretic

peptide data, which did not conform to the normal

distribution, and the Kruskal±Wallis H-test was there-

fore performed. Repeated measures ANOVA with

Student±Neuman±Keul post hoc analysis was

performed to compare between baseline and on-pacing

values. The correlation between atrial pressures and

natriuretic peptide levels was explored using multiple

regression analysis with dummy variables as described

by Glantz & Slinker (1990). Brie¯y, this method

examines the correlation between two variables within

each pig and corrects for between-animal variations so

that all measurements in each pig can be entered into

the analysis. The analysis can thus calculate the mean

regression line for all the pigs and test the signi®cance

of the slope and R2 value of this regression line. Missing

values are not tolerated in this analysis and were

therefore estimated using Neuman±Keuls approxima-

tion. The multiple regression analysis was performed

both on unadjusted values and after an exponential and

a logarithmic transformation of the peptide data. A

P-value <0.05 was considered statistically signi®cant.

All analyses were performed with SPSS statistical

analysis package (version 8.0, SPSS) except repeated

measures ANOVA which was performed using Primer of

Biostatistics (version 3.0, McGraw-Hill).

RESULTS

All the animals displayed a 1:1 conduction of pacing

throughout the study period. The mean heart rate and

the left and right atrial pressures from the six pigs with

functional implants are presented in Fig. 1. As the

®gure clearly illustrates, initiation of pacing produced a

prompt and signi®cant pressure increase in the left

atrium with only a slight further increase during the rest

of the pacing period. In the right atrium, there was an


Acta Physiol Scand 2000, 169, 95±102 W Qi et al. � Natriuretic peptide and atrial pressure

attenuated and more gradual rise in pressure

throughout the pacing period. The repeated measures

ANOVA test showed that there was a general increase in

right atrial pressure over time (P � 0.015), but the

individual time points were not signi®cantly different

from the mean baseline value on post hoc analysis. The

left atrial pressure responded more briskly to alterations

in pacing frequencies than the right atrial pressure. This

is shown more clearly in Fig. 2 which depicts the

alterations in atrial peptides, heart rate and atrial pres-

sures in one pig where the pacemaker rate was adjusted

down from 225 to 180 beats min)1 from day 5 to day

9. At the end of the study, both atrial pressures

decreased rapidly. The correlation between atrial

peptides and atrial pressures can be envisaged in Fig. 3

and was further examined using multiple regression

analyses with dummy variables to correct for between-

animal variations. Scatterplots of the unadjusted peptide

levels vs. atrial pressures (data not shown) suggested a

non-linear correlation. A logarithmic and exponential

transformation of the peptide data was therefore

performed prior to multiple regression analyses. The

best ®t and highest R2 values were obtained after a

logarithmic transformation of the peptide data.

However, all the analyses showed qualitatively the same

results as depicted in Fig. 3. Both atrial pressures were

signi®cantly correlated to all three peptides, with the

best correlation coef®cients observed for BNP followed

by NT-proANP. BNP showed a stronger correlation to

left atrial pressure than to right atrial pressure.

The results of ANP, NT-proANP and BNP

measurements from both paced and sham animals are

illustrated in Fig. 4. Three consecutive measurements

indicated a steady-state of natriuretic peptide concen-

trations in pacing group at baseline with no difference

between paced and sham animals for any of the peptides.

Plasma concentrations of all peptides increased signi®-

cantly during pacing with more than 50% of the

maximum increase occurring within the ®rst day of

pacing relative to the third baseline (ANP: 53.8 � 21.8±

95.9 � 30.9 pmol L)1, P < 0.05; NT-proANP:

1263 � 193±1824 � 269 pmol L)1, P < 0.01; BNP:

3.6 � 0.9±9.0 � 2.8 pmol L)1, P < 0.001). Twenty-

four hours after cessation of pacing, the plasma level of

BNP in the paced group was 2-fold that of the sham

group (4.7 � 1.8 vs. 2.4 � 0.4 pmol L)1, P < 0.05),

while the level of ANP was completely normalized

(33.3 � 13.1 vs. 32.5 � 8.6 pmol L)1) (Table 1).

Two animals died on the day of the ®nal haemo-

dynamic study, one of cardiac arrest during induction of

Figure 1 Graph depicting the mean left and right atrial pressures in

the six pigs with functional implants in (b) with the corresponding

heart rates in (a). Note the large and rapid increase in left atrial

pressure (j) with the onset of pacing compared with the smaller and

more gradual increase in right atrial pressure (h). Error bars represent

95% con®dence interval. * P < 0.05 vs. mean baseline.

Figure 2 Graph depicting the alterations in atrial pressures, heart rate

and natriuretic peptides in one pig. Note how the left atrial pressure

curve (dashed line, lower panel) mimics the heart rate curve during the

onset of pacing (day 0) and the latter adjustments of pacing frequency.

The right atrial pressure follows a similar, but attenuated course (solid

line, lower panel) with the alterations in pacing rate with a more

gradual increase during the latter period of constant high frequency

pacing. The levels of all the natriuretic peptides also exhibit a similar

pattern as the atrial pressures, consistent with atrial stretch as a main

stimulus for natriuretic peptide release.



anaesthesia, the other of myocardial pump failure

during catheterization. The results of the haemody-

namic measurements in the remaining animals are

presented in Table 1. Twenty-four hours after cessation

of pacing, cardiac ®lling pressures and pulmonary artery

pressure were all signi®cantly increased in the paced

pigs compared with sham pigs. Furthermore, cardiac

hypertrophy was evident in the pacing group with

increased heart to body weight ratio (7.6 � 0.03 g kg)1

vs. 6.2 � 0.01 g kg)1, P < 0.01).

DISCUSSION

Rapid atrial pacing in this pig model induced an

increase in atrial pressures with concomitant increases

in the circulating levels of the natriuretic peptides. The

most pronounced pressure increase was found in left

atrial pressure with more than 65% of the pressure

increase occurring within the ®rst day of pacing. The

response in right atrial pressure was more attenuated

and gradual throughout the pacing period. This pattern

was also seen when pacing rates were adjusted during

the pacing period and when pacing was stopped, with

more pronounced and rapid responses in the left than

in the right atrial pressure. These ®ndings corroborate

the observations of Stevens et al. (1996) who found that

while PCWP increased abruptly after onset of pacing,

there was no change in right atrial pressure over a 45-

min period of pacing in dogs. Likewise, Moe et al.

(1990) showed that the onset of pacing was associated

with an immediate rise (within 5 min) in PCWP

accompanied by only a slight increase in right atrial

Figure 3 Scatterplots showing the natriuretic peptide levels plotted as a function of the left and right atrial pressures, respectively. The mean

regression line with its corresponding equation, R2 and P-values from the multiple regression analysis with dummy variables are presented in each

scatterplot. The respective values from each individual pig are represented by the same symbol in all scatterplots.



pressure. The rapid rise in left atrial pressure with the

onset of pacing most probably relates to the shortening

of diastolic duration to a degree where left ventricular

relaxation and ®lling is impaired requiring higher ®lling

pressures. The divergence in the early response between

the two atria can be explained by the higher compliance

and lower afterload of the right ventricle. Furthermore,

the vascular compliance of the splanchnic venous bed

which buffers the right atrial volume changes is larger

than that of the pulmonary bed which buffers left atrial

volume changes (Shoukas 1982, Kjekshus et al. 1997).

The more gradual rise in the right atrial pressure may

re¯ect a degree of hypervolemia induced by the

increased sympathetic activity and activation of the

renin±angiotensin±aldosterone system as we have

shown previously in this model (Klinge et al. 1998).

On advice from the chief veterinarian of the animal

department, the pacemaker rates were temporarily

adjusted down in pigs that exhibited signs of decom-

pensated heart failure. As a consequence, the pigs

mimicked a patient population where adjustments of

pacemaker rates simulated intensi®ed treatment during

times of decompensation. Reducing pacing frequencies

led to decreases in atrial pressures, most markedly in

left atrial pressure. This effect was seen in all pigs that

underwent adjustments of pacing frequencies as

exempli®ed in Fig. 2.

Because adjustments of pacing frequencies were

carried out at varying timepoints, the increase in atrial

pressures and peptide levels seen in the individual pigs

during the periods of maximal pacing frequencies was

not evident in the ®gures depicting the mean pressures

and peptide levels. To examine the true correlation

between the atrial pressures and the various peptide

levels within each pig, we performed multiple regres-

sion analysis with dummy variables, to correct for

between-animal variation. BNP showed the strongest

correlation to atrial pressures with R2 values of 0.81 for

left atrial pressure compared with R2-values of 0.66 and

0.67 for ANP and NT-ANP, respectively. This

corroborates the ®ndings of Maeda et al. (1998) of BNP

as a better predictor of LVEDP than ANP in patients

with left ventricular dysfunction. One possible explan-

ation to these ®ndings may be that in failing hearts

Figure 4 Graph depicting the mean natriuretic peptide levels in

paced pigs (j, n � 10) and sham pigs (h, n � 7). Note the marked

initial increase in peptide levels with the onset of pacing and the

subsequent drop after cessation of pacing. Atrial natriuretic peptide

levels were completely normalized within 24 h post pacing. Error bars

represent 95% con®dence interval. # P < 0.05 vs. sham animals.

Sham group

(n = 7)

Paced group

(n = 8)

Body weight (kg) 42.6 � 2.2 43.7 � 2.5

Heart weight (g) 262 � 27 333 � 39 Heart rate (beats min)1) 121 � 26 124 � 22

Mean arterial pressure (mmHg) 82 � 15 91 � 6

Left ventricular end-diastolic pressure (mmHg) 2.7 � 1.9 13.1 � 2.7àCentral venous pressure (mmHg) 2.2 � 1.6 6.7 � 1.5àPulmonary artery pressure (mmHg) 14.4 � 3.4 26.6 � 6.7 Pulmonary capillary wedge pressure (mmHg) 3.1 � 2.3 14.6 � 3.9àCardiac output (L min±1) 5.3 � 0.5 5.1 � 0.4

Atrial natriuretic peptide (pmol L±1) 32.5 � 8.6 33.3 � 13.1

N-terminal proatrial natriuretic peptide (pmol L±1) 672 � 171 912 � 195

Brain natriuretic peptide (pmol L±1) 2.4 � 0.4 4.7 � 1.8*

Data are mean � 95% con®dence interval, * P < 0.05 vs. sham group; P < 0.01 vs. sham group;

à P < 0.001 vs. sham group.

Table 1 Characteristics of paced

group vs. sham group 24 h after

termination of pacing



BNP is produced to a larger degree in ventricular

cardiomyocytes than ANP (Mukoyama et al. 1991).

BNP may therefore better re¯ect left ventricular

dysfunction than ANP.

Twenty-four hours after termination of pacing,

plasma ANP had returned to control levels while BNP

still remained signi®cantly higher in the paced animals

than sham animals. Moe et al. (1993) observed a similar

delayed decline of plasma BNP 48 h after cessation of

pacing. While left atrial stretch may decrease rapidly

when the pacing stops, left ventricular dysfunction may

persist, leading to sustained BNP release from this

region. This difference between the peptides may

re¯ect a slower clearance of BNP than of ANP from

the circulation owing to its lower binding af®nity to the

natriuretic peptide receptor-C (Mukoyama et al. 1991).

Furthermore, persistent increases in atrial pressures

may attenuate the ANP secretion in response to further

increases, in pressure (Moe et al. 1991). Finally, a recent

study by Clerico & Iervasi (1995) suggests that CHF

augment the peripheral degradation and clearance of

ANP. This may explain why ANP levels are normalized

24 h after cessation of pacing in spite of persistent and

signi®cant increases in LVEDP and CVP at that time

compared with controls.

Among study limitations, several points should be

discussed. The radio-telemetry pressure monitoring

system (Data Science International, USA) has previ-

ously been validated in dogs. Arterial blood pressures

and heart rates recorded by the telemetry system agreed

closely with simultaneous measurements obtained by

catheterization during a 17-week period (Truett & West

1995). To our knowledge, this is the ®rst report of

continuous monitoring of atrial pressures by telemetry

in conscious animals. We found a great degree of

variability of the individual pressure tracings. A large

part of the variation occurred synchronously in both

atria with a pattern consistent with alterations in

posture (Gibbs et al. 1989) and grunting. In addition to

the physiological alterations in atrial pressures owing to

altered cardiac ®lling induced by a change in posture,

there were also changes in implant measurements

related to alterations in the position of the pressure

sensors in the implant relative to the tip of the liquid-

®lled catheters in the atria. Thus, during rest the

implants would over-or underestimate true atrial pres-

sures corresponding to the vertical distance from the

implant sensors located in the left thoracic ¯ank to the

atria. If the pigs rested equally on either side the effect

would cancel out owing to the use of a 24-h median

measurement of atrial pressures. However, we observed

that the pigs seemed to prefer to lie on their right side

(where they had no implant) when resting and this may

have induced a systemic underestimation of the atrial

pressures. There were also some unphysiological and

non-synchronous pressure-artefacts, probably owing to

trapping of the catheters in the trabeculae of the atria.

These latter artefacts were eliminated as described in

methods, but in a few instances it left a limited number

of observations on which the 24-h median value was

based.

The recovery of BNP in the extraction procedure

was only 48% and was not corrected for. Thus, the true

plasma BNP value would be approximately twice that

reported. However, the reproducibility of the assay was

excellent with an inter- and intra-assay variability of 9.0

and 5.5%, respectively.

We conclude that in this porcine rapid pacing model

with continuous monitoring of atrial pressures, we

showed signi®cant increases in natriuretic peptides and

atrial pressures with the evolvement of CHF. Left atrial

pressure responded stronger and more rapidly to

alterations in the rate of pacing than right atrial pres-

sure. The strongest correlation between natriuretic

peptides and atrial pressures was found between BNP

and left atrial pressure suggesting that BNP may be a

more sensitive marker of cardiac ®lling pressures than

ANP or NT-proANP. This may re¯ect a more prom-

inent role of ventricular production of BNP during

CHF, as well as differences in peripheral degradation

and stimulus-responsiveness of the peptides during

CHF.

We would like to express our gratitude to Camilla Sùrlie, Ellen Lund

Sagen, Hanne Schulz Jensen for their substantial technical assistance,

to Vivi Bull. Stubberud and Roger édegaÊrd for providing excellent

help and surgical cooperation, to chief veterinarian Dag Sùrensen and

his staff for their help with the animal handling, and to Medtronic

Norway for supplying pacemakers and pacing electrodes. Wei Qi was

supported by a fellowship from Norwegian State Educational Fund.

Harald Kjekshus was supported by a fellowship from The Norwegian

Council for Cardiovascular Diseases.

REFERENCES

Chang, M.S., Lowe, D.G., Lewis, M., Hellmiss, R., Chen, E. &

Goeddel, D.V. 1989. Differential activation by atrial and

brain natriuretic peptides of two different receptor

guanylate cyclases. Nature 341, 68±72.

Clerico, A. & Iervasi, G. 1995. Alterations in metabolic

clearance of atrial natriuretic peptides in heart failure: how

do they relate to the resistance to atrial natriuretic peptides?

J Card Fail 1, 323±328.

de Bold, A.J., Borenstein, H.B., Veress, A.T. & Sonnenberg,

H. 1981. A rapid and potent natriuretic response to

intravenous injection of atrial myocardial extract in rats.

Life Sci 28, 89±94.

Gibbs, J.S., Cunningham, D., Shapiro, L.M., Park, A., Poole-

Wilson, P.A. & Fox, K.M. 1989. Diurnal variation of

pulmonary artery pressure in chronic heart failure. Br Heart

J 62, 30±35.

Glantz, S.A. & Slinker, B.K. 1990. Primer of Applied

Regression and Analysis of Variance. 381±390.



Hall, C., Aaberge, L. & Stokke, O. 1995. In vitro stability of

N-terminal proatrial natriuretic factor in unfrozen samples:

an important prerequisite for its use as a biochemical

parameter of atrial pressure in clinical routine. Circulation 91,

911.

Hall, C., Rouleau, J.L., Moye, L., de Champlain, J., Bichet, D.,

Klein, M., Sussex, B., Packer, M., Rouleau, J., Arnold, M.

O., Lamas, G.A., Sestier, F., Gottlieb, S.S., Wun, C.C. &

Pfeffer, M.A. 1994. N-terminal proatrial natriuretic factor.

An independent predictor of long-term prognosis after

myocardial infarction. Circulation 89, 1934±1942.

Kjekshus, H., Risoe, C., Scholz, T. & Smiseth, O.A. 1997.

Regulation of hepatic blood Volume ± contributions from

active and passive mechanisms during catecholamine and

sodium nitroprusside infusion. Circulation 96, 4415±4423.

Klinge, R., Hystad, M., Kjekshus, J., Karlberg, B. E.,

Djoseland, O., Aakvaag, A. & Hall, C. 1998. An

experimental study of cardiac natriuretic peptides as

markers of development of congestive heart failure. Scand J

Clin Lab Invest 58, 683±692.

Maack, T., Suzuki, M., Almeida, F.A., Nussenzveig, D.,

Scarborough, R.M., McEnroe, G.A. & Lewicki, J.A. 1987.

Physiological role of silent receptors of atrial natriuretic

factor. Science 238, 675±678.

Maeda, K., Tsutamoto, T., Wada, A., Hisanaga, T. &

Kinoshita, M. 1998. Plasma brain natriuretic peptide as a

biochemical marker of high left ventricular end-diastolic

pressure in patients with symptomatic left ventricular

dysfunction. Am Heart J 135, 825±832.

Moe, G.W., Angus, C., Howard, R.J., de Bold, A.J. &

Armstrong, P.W. 1990. Pathophysiological role of changing

atrial size and pressure in modulation of atrial natriuretic

factor during evolving experimental heart failure. Cardiovasc

Res 24, 570±577.

Moe, G.W., Grima, E.A., Angus, C., Wong, N.L., Hu, D.C.,

Howard, R.J. & Armstrong, P.W. 1991. Response of atrial

natriuretic factor to acute and chronic increases of atrial

pressures in experimental heart failure in dogs. Role of

changes in heart rate, atrial dimension, and cardiac tissue

concentration. Circulation 83, 1780±1787.

Moe, G.W., Grima, E.A., Wong, N.L., Howard, R.J. &

Armstrong, P.W. 1993. Dual natriuretic peptide system in

experimental heart failure. J Am Coll Cardiol 22, 891±898.

Mukoyama, M., Nakao, K., Hosoda, K., Suga, S., Saito, Y.,

Ogawa, Y., Shirakami, G., Jougasaki, M., Obata, K., Yasue,

H., Kambayashi, Y., Inouye, K. & Imura, H. 1991. Brain

natriuretic peptide as a novel cardiac hormone in humans.

Evidence for an exquisite dual natriuretic peptide system,

atrial natriuretic peptide and brain natriuretic peptide. J Clin

Invest 87, 1402±1412.

Mukoyama, M., Nakao, K., Saito, Y., Ogawa, Y., Hosoda, K.,

Suga, S., Shirakami, G., Jougasaki, M. & Imura, H. 1990.

Increased human brain natriuretic peptide in congestive

heart failure. N Engl J Med 323, 757±758.

Nelesen, R.A., Dimsdale, J.E. & Ziegler, M.G. 1992. Plasma

atrial natriuretic peptide is unstable under most storage

conditions. Circulation 86, 463±466.

Pemberton, C.J., Yandle, T.G., Rademaker, M.T., Charles, C.

J., Aitken, G.D. & Espiner, E.A. 1998. Amino-terminal

proBNP in ovine plasma: evidence for enhanced secretion

in response to cardiac overload. Am J Physiol 275, 1200±

1208.

Rademaker, M.T., Charles, C.J., Kosoglou, T., Protter, A.A.,

Espiner, E.A., Nicholls, M.G. & Richards, A. M. 1997.

Clearance receptors and endopeptidase: equal role in

natriuretic peptide metabolism in heart failure. Am J Physiol

273, 2372±2379.

Rodeheffer, R.J., Tanaka, I., Imada, T., Hollister, A.S.,

Robertson, D. & Inagami, T. 1986. Atrial pressure and

secretion of atrial natriuretic factor into the human central

circulation. J Am Coll Cardiol 8, 18±26.

Saito, Y., Nakao, K., Itoh, H., Yamada, T., Mukoyama, M.,

Arai, H., Hosoda, K., Shirakami, G., Suga, S., Minamino,

N., Kangawa, K., Matsuo, H. & Imura, H. 1989. Brain

natriuretic peptide is a novel cardiac hormone. Biochem

Biophys Res Commun 158, 360±368.

Shoukas, A.A. 1982. Carotid sinus baroreceptor re¯ex control

and epinephrine. In¯uence on capacitive and resistive

properties of the total pulmonary vascular bed of the dog.

Circ Res 51, 95±101.

Stevens, T.L., Rasmussen, T.E., Wei, C.M., Kinoshita, M.,

Matsuda, Y. & Burnett, J.C. Jr. 1996. Renal role of the

endogenous natriuretic peptide system in acute congestive

heart failure. J Card Fail 2, 119±125.

Sundsfjord, J.A., Thibault, G., Larochelle, P. & Cantin, M.

1988. Identi®cation and plasma concentrations of the

N-terminal fragment of proatrial natriuretic factor in man.

J Clin Endocrinol Metab 66, 605±610.

Truett, A.A. & West, D.B. 1995. Validation of a

radiotelemetry system for continuous blood pressure

and heart rate monitoring in dogs. Lab Anim Sci 45,

299±302.

Tsutamoto, T., Wada, A., Maeda, K., Hisanaga, T., Maeda, Y.,

Fukai, D., Ohnishi, M., Sugimoto, Y. & Kinoshita, M.

1997. Attenuation of compensation of endogenous cardiac

natriuretic peptide system in chronic heart failure:

prognostic role of plasma brain natriuretic peptide

concentration in patients with chronic symptomatic left

ventricular dysfunction. Circulation 96, 509±516.

Yoshimura, M., Yasue, H., Morita, E., Sakaino, N., Jougasaki,

M., Kurose, M., Mukoyama, M., Saito, Y., Nakao, K. &

Imura, H. 1991. Hemodynamic, renal, and hormonal

responses to brain natriuretic peptide infusion in patients

with congestive heart failure. Circulation 84, 1581±1588.



cardiac natriuretic peptides and continuously monitored atrial pressures during chronic rapid pacing...

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