Francis Solti

Intrapericardial infusion of endothelin-1 induces ventricular arrhythmias in dogs.

OBJECTIVES Recently, extremely high levels of endothelin-1 (ET-1) were detected in the pericardial fluid of patients with heart disease; however, the pathophysiological importance of this finding is not known. The present study was designed to characterize ET-1 levels in canine pericardial fluid and to investigate the effects of local high concentrations of exogenous ET-1 in vivo. METHODS In anesthetized, open-chest dogs ET-1 (Groups 1 and 2: 11 and 33 pmol.kg-1.min-1; n = 6 and 6, respectively) or physiological saline (Group 3, n = 5) were infused into the closed pericardial sac for 40 min. In serial pericardial fluid and aortic blood plasma samples, ET-1 levels were measured by radioimmunoassay, and analysed by high-performance liquid chromatography (HPLC). Systemic arterial blood pressure, heart rate, cardiac output (CO), standard ECG and right ventricular endocardial monophasic action potentials (MAPs) were recorded. RESULTS Basal pericardial fluid ET-1 levels were significantly higher than respective plasma levels (342 +/- 210 vs. 8.0 +/- 5.2 pmol.l-1, n = 14, P < 0.001. In HPLC analysis pericardial fluid ET-1 was indistinguishable from ET-1(1-21). Infusion of exogenous ET-1 into the pericardial space induced ventricular arrhythmias in all instances, which were associated with 9.7-fold increase in pericardial fluid ET-1 levels. Ventricular tachycardias developed in 9 of 12 animals. The arrhythmogenic effect of ET-1 was more apparent in dogs with the larger dose. Before the onset of arrhythmias, intrapericardial infusion of ET-1 increased QT time (Group 1: 207 +/- 18 to 230 +/- 23 ms, P < 0.01; Group 2: 220 +/- 12 to 277 +/- 17 ms, P < 0.01) and MAP duration at 90% repolarization (at 300 ms cycle length) (Group 1: 192 +/- 9 to 216 +/- 9 ms, P < 0.01; Group 2: 205 +/- 9 to 255 +/- 9 ms, P < 0.001). Hemodynamic variables did not change significantly prior to the onset of ventricular tachyarrhythmias. In Group 3, arrhythmias were not observed and all electrophysiological and hemodynamic parameters remained unchanged. CONCLUSIONS Administration of exogenous ET-1 into the pericardial space induces ventricular arrhythmias associated with prolongation of QT time and MAP duration. Whether pericardial fluid ET-1 under pathophysiological conditions can ever reach sufficiently high levels to induce ventricular arrhythmias remains to be elucidated.

Investigating the dual nature of endothelin-1: ischemia or direct arrhythmogenic effect?

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide, which may also elicit severe ventricular arrhythmias. The aims of our study were to compare the effects of total left anterior descending coronary artery (LAD) occlusion to intracoronary (ic.) ET-1 administration and to investigate the pathomechanism of ET-1 induced arrhythmias in 3 groups of anesthetized, open-chest mongrel dogs. In group A (n=10) a total LAD occlusion was carried out for 30 min, followed by a 60 min reperfusion period. In groups B and C ET-1 was administered into LAD for 30 min at a rate of 30 pmol/min (n=6) and 60 pmol/min (n=8). Epi- and endocardial monophasic action potential (MAP) recordings were performed to detect electrophysiologic changes and ischemia Blood samples for lactate measurements were collected from the coronary sinus (CS) and from the femoral artery. Infrared imaging was applied to follow epimyocardial heat emission changes. At the end of the ET-1 infusion period coronary blood flow (CBF) was reduced significantly in groups B and C (deltaCBF30MIN B: 21+/-2%, p<0.05; C: 35+/-2%, p<0.05), paralleled by a significant epimyocardial temperature decrease in group C (deltaT30MIN: -0.65+/-0.29 degrees C, p<0.05). Two dogs died of ventricular fibrillation (VF) in the reperfusion period in group A. Ventricular premature contractions and non-sustained ventricular tachycardic episodes appeared in group B, whereas six dogs died of VF in group C. Significant CS lactate level elevation indicating ischemia was observed only in group A from the 30th min occlusion throughout the reperfusion period (control vs. 30 min: 1.3+/-0.29 vs. 2.2+/-0.37 mmol/l, p<0.05). Epi- and endocardial MAP durations (MAPD90) and left ventricular epicardial (LV(EPI)) upstroke velocity decreased significantly in group A in the occlusion period. ET-1 infusion significantly increased LV(EPI) MAPD90 in group B and both MAPD90-s in group C. In conclusion, ischemic MAP and CS lactate changes were observed only in group A. Although ET-1 reduced CBF significantly in groups B and C, neither MAP nor lactate indicated ischemic alterations. ET-1 induced major ventricular arrhythmias appeared before signs of myocardial ischemia developed, though reduced CBF presumably contributed to sustaining the arrhythmias.

Ventricular tachycardias induced by intracoronary administration of endothelin-1 in dogs.

Summary: In 12 anesthetized, open-chest mongrel dogs, endothelin-1 (ET-1) was infused into the left anterior descending coronary artery through an indwelling catheter at a dose of 30 pmol min-1 for 30 min (n = 8). In four dogs the ET-1 dose was increased to 60 pmol/min for 10 min. Programmed electrical stimulation was used for electrophysiologic studies. Coronary blood flow was reduced by 32% on average without any ischemic ECG signs. QT time (186 ± 3 ms vs. 218 ± 6, p < 0.05, and 225 ± 9, p < 0.05, p < 0.05). Ventricular irritability increased in all cases; ventricular extrasystoles, and nonsustained and sustained tachycardias occurred and, in 11 cases, ventricular fibrillation terminated the experiments. In two dogs, early after depolarization was recorded. Therefore, ET-1 is capable of inducing fatal ventricular arrythmias at least partly independent of its vasoconstrictor effect. QT prolongation appears to have a pathophysiologic role in this arrythmogenic effect.

Mechanism of endothelin-induced malignant ventricular arrhythmias in dogs

The development of ventricular tachyarrhythmias caused by low-dose intracoronary infusion of endothelin-1 (ET-1) has recently been observed in dogs. The aim of the present study was to investigate the pathomechanism of ET-1-induced ventricular arrhythmias in 32 anesthetized, open-chest mongrel dogs in group A (n = 14) without, in group B (n = 14), and in group C (n = 4 control) with atrioventricular node ablation. The coronary blood flow (CBF) was measured in the left anterior descending (LAD) coronary artery by an electromagnetic flowmeter. Standard ECG, atrial and ventricular electrograms, and in groups B and C endocardial and epicardial monophasic action potentials (MAPs) were recorded. ET-1 was administered into the LAD at a low dose (30-60 pmol/min). At the time of the appearance of premature beats, CBF was only slightly decreased. The effective ventricular refractory period did not change significantly. Onset of spontaneous polymorphic and monomorphic sustained ventricular tachycardia (sVT) was observed in five dogs without bradycardia and in nine dogs with bradycardia. VTs in dogs with complete AV block were longer and slower. In most of the cases, ventricular fibrillation occurred. ET-1 treatment resulted in a significant increase in MAP 90% duration (255 +/- 9 vs. 290 +/- 8 ms endocardial, 244 +/- 10 vs. 292 +/- 12 epicardial; p < 0.05) at 70 beats/min ventricular pacing. In eight cases (group B), third-phase early afterdepolarization could be recorded. According to our results, the mechanism of ET-1-induced arrhythmias appears to be based on prolongation of MAP duration and development of afterdepolarizations.

Bradycardia increases the arrhythmogenic effect of endothelin

The effect of permanent bradycardia on the proarrhythmic action of endothelin-1 (ET) was investigated in 24 open-chest anesthetized mongrel dogs. In 12 dogs, permanent bradycardia was induced by radiofrequency ablation of the AV node and the hearts were paced at 70 beats/min. ET (60 pmol/min) was infused into the left anterior descending coronary artery. Blood pressure, coronary blood flow (CBF), and atrial and ventricular epicardial surface ECG were recorded continuously. Polymorphous ventricular tachycardia developed in every dog with permanent bradycardia, and ventricular fibrillation terminated the experiments in 11 cases. Bradycardia prolonged the basal QT but there was no difference in the frequency corrected QTc time between the two groups. ET prolonged the QT time in a similar fashion in both groups. In the control group, six dogs developed sustained ventricular tachycardias and ventricular fibrillation occurred in nine cases. EADP was found in six cases of eight registered. Signs of myocardial ischemia did not accompany the development of arrhythmias. We conclude that permanent bradycardia augments the direct proarrhythmic effect of ET in dogs.

Verapamil reduces the arrhythmogenic effect of endothelin

In a previous study we established that endothelin-1 (ET-1) can induce characteristic ventricular tachycardias (VT) with significant prolongation of QT and QTc time. In this investigation we studied the role of CA2+ channels in the pro-arrhythmic effects of ET-1. In 24 anesthetized, open-chest mongrel dogs, ET-1 was administered into the left anterior descending coronary artery at a comparatively low dose (60 pmol/min) for 30 min. Twelve dogs received the Ca(2+)-channel blocker verapamil (0.4 mg/kg) before ET-1 application. The following parameters were recorded continuously over the infusion period: systemic arterial blood pressure, coronary blood flow, surface ECG leads, epicardial atrial and ventricular electrograms, and right and left ventricular endocardial monophasic action potentials (MAP). Electrophysiologic studies were performed by programmed electrical stimulation of the heart. Blockade of myocardial Ca2+ channels attenuated the arrhythmogenic action of ET-1. After verapamil administration to ET-1-treated dogs, sustained VT did not appear and ventricular fibrillation (VF) developed only in two dogs. In the control group serious and sustained VT and VF developed in nine animals. It is noteworthy that verapamil did not prevent ET-1-induced prolongation of QT time. The results appear to prove that myocardial Ca2+ channels are involved in the proarrhythmic effect of ET-1.

Potential pathophysiologic role of endothelin-1 in canine pericardial fluid

Recently, extremely high levels of endothelin-1 (ET-1) were detected in the pericardial fluid of patients undergoing cardiac surgery. This study was designed to assess the pathophysiologic importance of this finding by infusing ET-1 into the closed pericardial sac of anesthetized dogs. Systemic arterial blood pressure, heart rate, and standard ECG were recorded. Intrapericardial infusion of ET-1 (11 and 33 pmol/kg/min; n = 4/4) for 40 min induced ventricular arrhythmias in all instances. The lower dose of ET-1 induced a substantial number of ventricular extrasystoles, couplets, and triplets. In one instance, ventricular extrasystoles accelerated into nonsustained ventricular tachycardia (VT). In animals receiving the higher dose, nonsustained VTs occurred regularly, whereas sustained VTs were detected in two of four animals. Before the onset of arrhythmias, QT time was significantly prolonged [ET-1 (11 pmol/kg/min) 180 +/- 12 to 198 +/- 10 ms, p < 0.05; ET-1 (33 pmol/kg/min) 192 +/- 15 to 233 +/- 13 ms, p < 0.01]. Hemodynamic variables did not change significantly before the onset of ventricular arrhythmias. Our results show that administration of exogenous ET-1 into the pericardial space induces ventricular arrhythmias associated with prolongation of QT time.

Fundamental electrophysiological differences between low-dose intracoronary endothelin-1 infusion and myocardial ischemia revealed by multiple monophasic action potential recording

We observed that heterozygous knockout (+/-, KO) of either endothelin-A- (ET(A)) or -B- (ET(B)) receptors significantly reduced the pressor responses to systemically administered endothelin-1 (ET-1) in ET(A) or ET(B) (+/-) KO mice when compared to wild-type (WT) mice (data not shown). Also, we observed that basal mean arterial pressure (MAP) is significantly higher in ET(B) (+/-) (92.7 +/- 1.2 mmHg) (n = 53, p < 0.05) but not ET(A) (+/-) KO mice (70.6 +/- 1.8 mmHg) (n = 23) when compared to their anaesthetized WT littermates (70.1 +/- 0.7 mmHg) (n = 118). A 90 min treatment with either BQ-123 (10 mg/kg), an ET(A)-selective antagonist, or BQ-928 (10 mg/kg), a mixed ET(A)/ET(B) antagonist, administered intraperitoneally, significantly reduced basal MAP of ET(B) (+/-) KO mice almost to the level of their WT treated counterparts (94.9 +/- 4.9 mmHg) (n = 6) vs (+ BQ-123: 59.7 +/- 0.3 mmHg, n = 8); (+ BQ-928: 72.4 +/- 2.6 mmHg, n = 5). It is worthy of note that BQ-123 significantly reduced basal MAP in WT mice but to a lesser extent than in ET(B) (+/-) KO mice (69.6 +/- 2.3 mmHg, n = 8) vs (+ BQ-123: 57.3 +/- 1.4 mmHg, n = 8). In contrast, the ET(B)-selective antagonist, BQ-788 (10 mg/kg i.p.), had no significant effect on MAP even after 90 min of treatment (ET(B) (+/-) KO: (92.3 +/- 2.3 mmHg, n = 6) vs (+ BQ-788: 89.7 +/- 3.1 mmHg, n = 6); WT: (70.5 +/- 3.7 mmHg, n = 7) vs (+ BQ-788: 71.2 +/- 2.0 mmHg, n = 6). Therefore heterozygous KO of either ET(A)- or ET(B)-receptors significantly alters the phenotypic pressor properties of ET-1. We also suggest that there is less ET clearance in ET(B) (+/-) KO mice than in WT mice, which can explain the ET(A)-dependent hypertensive state of the former strain.We evaluated the role of endothelin-B- (ET(B)) receptor-mediated action in the development and maintenance of deoxycorticosterone acetate (DOCA)-salt-induced hypertension, cardiovascular hypertrophy and renal damage, using the spotting lethal (sl) rat which carries a naturally occurring deletion in the ET(B)-receptor gene. Homozygous (sl/sl) rats exhibit abnormal development of the neural crest-derived epidermal melanocytes and the enteric nervous system (ENS), and do not live beyond 1 month because of intestinal aganglionosis and resulting intestinal obstruction. Therefore, the dopamine-beta-hydroxylase (D betaH) promoter was used to direct ET(B) transgene expression in sl/sl rats to support normal ENS development. D betaH-ET(B) sl/sl rats live into adulthood and are healthy, expressing ET(B)-receptor in adrenals and other adrenergic neurons. When homozygous (sl/sl) and wild-type (WT) (+/+) rats, all of which were transgenic, were treated with DOCA and salt for 4 weeks, the homozygous rats exhibited significantly earlier and higher increases in systolic blood pressure than WT rats. The daily oral administration of ABT-627, a selective ET(A)-receptor antagonist, almost completely suppressed the DOCA-salt-induced hypertension in both groups. Renal dysfunction and histological damage induced by DOCA-salt treatment were more severe in homozygous than in WT rats. Increased and marked vascular hypertrophy of the aorta was also observed in homozygous rats, compared with WT rats. Renal and vascular injuries induced by DOCA and salt were significantly improved by ABT-627 administration. We propose that ET(B)-receptor-mediated actions are protective factors in the pathogenesis of DOCA-salt-induced hypertension. ET(A)-mediated actions are at least partly responsible for the increased susceptibility to DOCA-salt-induced hypertension and related tissue injuries in ET(B)-receptor-deficient rats.

Applying cardiothermography and electrophysiology to differentiate between the ischemic and arrhythmogenic actions of endothelin-1

Endothelin-1 (ET-1) is the strongest vasoconstrictor peptide isolated so far, which has a known arrhythmogenic property, as well. Intracoronary ET-1 infusion may cause ventricular premature beats (VES), ventricular tachycardia (VT) and ventricular fibrillation (VF). The aim of our study was to compare the thermographic and electrophysiologic changes during left anterior describing coronary artery (LAD) occlusion and ic. ET-1 administration. The measurements were performed on 16 sodium-pentobarbital anesthetized, open- chest dogs. The dogs were divided into 2 groups. In group A LAD occlusion was carried out for 30 minutes, followed by a 60 min reperfusion period. In group B ET-1 was administered into LAD at 60 pmol/min dose. Arterial blood pressure, coronary blood flow (CBF), heart rate (HR) and standard ECG were monitored. IR thermography was applied to follow epimyocardial heat emission changes. To determine the electrophysiological changes an endocardial monophasic action potential (MAP) electrode was inserted into the right ventricle and an MAP electrode was placed onto the left ventricle and an MAP electrode was placed onto the left ventricular epicardium. In group A CBF returned to baseline 20 minutes after releasing the occlusion. Ic. ET-1 infusion significantly reduced CBF in group B. Epimyocardial temperature decreased in both groups. In group A ventricular extrasystoles were noticed. In group B ventricular techycardias occurred with satisfactory CBF in 4 cases. In 5 dogs VF was observed. MAP duration 90 (MAPD90) decreased significantly in group A whereas significant increase was observed in group B. The left ventricular epicardial upstroke velocities correlated excellently with the epimyocardial temperature changes. Our result suggests that the decrease of epimyocardial heat emission and upstroke velocity correlates well in both groups, indicating ischemia, whereas the lack of the other ischemic MAP signs and the change of MAPD90 in the opposite direction suggests a different arrhythmia pathomechanisms in the ET group. Cardiothermography proved to be a useful tool in monitoring epimyocardial temperature changes during coronary artery occlusion and ET-1 induced vasoconstriction.