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Angiocardiography is an important diagnostic modality for evaluation of heart disease. It is well known that the concentration of plasma atrial natriuretic peptide (ANP) increases after injection of contrast medium. On the other hand, some patients with hypertension, heart failure or cardiac hypertrophy have an increased plasma ANP concentration at baseline; however, whether ANP increases after angiography in these patients is unknown.
To investigate changes in plasma ANP concentrations after angiocardiography in patients with high ANP concentrations at baseline.
Plasma ANP concentrations of 32 patients with angina pectoris were measured before and after angiocardiography. They were then classified into two groups according to their ANP concentration before examination.
ANP concentration after the injection of contrast medium increased significantly in patients with normal ANP concentrations before angiography but did not change in patients with high ANP concentrations at rest.
These results suggest that the absence of an increase in ANP after angiography may in part be due to reduced sensitivity to the angiography stimulus or to an already maximal activation of ANP secretion at baseline.
Angiocardiography is an important diagnostic modality for evaluation of ischemic heart disease. The injection of radiographic contrast medium produces transient hemodynamic changes, resulting in an increase in mean arterial pressure, mean pulmonary arterial pressure, mean pulmonary capillary wedge pressure, cardiac output and stroke volume. Subsequently, there is a gradual return to preinjection concentrations within 15 to 20 min (1). It has also been shown that radiocontrast medium induces a pronounced diuresis (2).
Atrial natriuretic peptide (ANP) is a cardiac hormone that helps to maintain circulatory homeostasis and changes myocardial performance by modulating cardiac preload and afterload through diuresis or natriuresis, vasodilation and suppression of the autonomic pressure response (3). It is well known that the plasma concentration of ANP increases after injection of contrast medium (2,4).
High plasma ANP concentrations at rest are seen in several pathophysiological conditions such as hypertension and heart failure, and are caused by chronic basal upregulation of ANP synthesis (5–7). Hemodynamics in some patients with these conditions are worsened after angiocardiography because of volume overload with contrast medium. In such cases it is possible that high ANP concentration at baseline cannot increase more to maintain circulatory homeostasis after injection of contrast medium. The aim of this study was to investigate changes in plasma ANP concentrations after angiocardiography in patients with high ANP concentrations at baseline.
Thirty-two consecutive patients with stable angina pectoris took part in the study. Patients with a history of cirrhosis, renal failure or recent myocardial infarction were excluded. Informed consent was obtained from all patients.
All patients underwent routine cardiac catheterization through the femoral approach for evaluation of ischemic heart disease. Hemodynamic measurements, coronary angiography and left ventriculography were carried out. The patients lay in the supine position for 1 h before and during the catheter examination. The total mean radiocontrast medium (iopamidol 370 mg I/mL) volume given was 100 mL. Ten millilitres of blood was drawn from a femoral artery for ANP analysis just before and after examination. Plasma ANP concentrations were determined using a specific immunoradiometric assay kit (Shionoria ANP; Shionogi Co, Japan), and the cut-off value in this assay was 43.0 pg/mL, as described elsewhere (8).
The patients were classified into two groups according to their ANP concentration before examination: those with a concentration less than 43.0 pg/mL (group N; n=24) and those with a concentration greater than 43.0 pg/mL (group H; n=8). The changes in ANP concentrations in the two groups were then investigated. An unpaired or paired Student’s t test (STATVIEW 4.02, Abacus Concepts, USA) was used for comparisons between the groups. P<0.05 was considered significant. Results are expressed as mean ± SD.
Clinical characteristics and hemodynamics of the patients are shown in the Table 1. Nine of 24 patients (38%) in group N and five of eight (63%) in group H had hypertension. One patient in group H had atrial fibrillation; the others were in normal sinus rhythm.
The mean plasma ANP concentrations before angiography were 22.4±12.2 pg/mL in group N and 74.3±18.9 pg/mL in group H (P<0.0001). The mean right atrial pressure and the pulmonary capillary wedge pressure in group H were significantly higher than in group N (P<0.01). These hemodynamic measurements correlated significantly with ANP concentrations (P<0.001), while the correlation between left ventricular end-diastolic pressure and ANP concentration was not significant (Figure 1). After injection of contrast medium the plasma ANP concentration in group N increased by 58% (+10.7±18.2 pg/mL, P<0.01), while in group H it decreased by 15% (−7.8±25.8 pg/mL, P=0.42) (Figure 2).
Injection of hyperosmolar contrast medium is followed by a rapid movement in body water from the intracellular and extravascular spaces to the intravascular space (4). Plasma ANP concentrations correlated well with mean right atrial and pulmonary capillary wedge pressures, as shown in this study and others (9). The change in ANP concentrations in group N after angiography could have been caused by increased intravascular volume and subsequent atrial overload. An increase in plasma ANP may play a part in maintaining circulatory homeostasis and changing cardiac performance during and after angiography. Notably, there was no significant change in ANP concentrations in group H after injection of contrast medium.
Increased plasma ANP concentrations at rest are seen in several pathophysiological conditions (5–7). Furthermore, increased ANP concentrations are related to left ventricular dysfunction (10,11) and correlate with a poor cardiovascular prognosis. Thus, ANP may aid in risk stratification and choice of treatment (12). Injection of contrast medium has been shown to have diuretic and natriuretic effects (2). An increase in plasma ANP concentration may play a part in this renal effect because ANP has similar effects after intravenous injection (9,13). Therefore, the absence of or increase in ANP after angiography may be one cause of pulmonary congestion in some patients with heart disease.
Although the pathophysiological significance of the absence of ANP increase after angiography is uncertain, it should be noted that ANP is stored in numerous specific granules and is rapidly released via a regulated pathway in atrial myocytes (14,15). In group H, ANP concentrations were even higher than in group N, even after angiography. These findings seem to be explained by reduced sensitivity to the contrast medium stimulus or in terms of an already maximal activation of ANP secretion at baseline in patients with high ANP concentrations at rest. Therefore, intravenous infusion of ANP for these patients undergoing cardiac catheterization might be a useful preventive strategy against hemodynamic failure after injection of contrast medium. Further studies are required to clarify this interesting issue.