Blood pressure control by the renin-angiotensin system in normotensive subjects. Assessment by angiotensin converting enzyme and renin inhibition

Experience with two different nonthoracotomy systems for implantable defibrillator in 170 patients

Implantation of a nonthoracotomy system (Medtronic PCD or CPI Endotak) was attempted in 170 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) not requiring concomitant cardiac surgery. A nonthoracotomy system could be successfully implanted in 95 of the 115 patients with the PCD system and 49 of 55 patients receiving the Endotak lead system. In 26 patients with failed nonthoracotomy system because of defibrillation threshold (DFT) > 25 joules (J), an epicardial system was implanted at the same setting. Patients receiving the two lead systems were comparable with regard to age, sex, and ejection fraction. However, since the PCD system offers tiered therapy multiprogrammable options, all attempts were made to implant this lead system in patients with VT that could be pace terminated. Mean DFT (15 +/- 4.7 vs 17 +/- 4.6 J; P = 0.03) and implant time (2.5 +/- 0.6 vs 3.3 +/- 0.7 hours; P = 0.02) were less with the Endotak lead system. There was no perioperative mortality. During a mean follow-up of 20 +/- 4 months, there were eight instances of lead dislodgment in patients receiving the PCD system. There were four nonsudden cardiac deaths and one sudden death in the Endotak group and three nonsudden deaths in the PCD group. Sudden cardiac death and total survival using the intention-to-treat analysis during this follow-up period were 99% and 95%, respectively. In conclusion, successful implantation, perioperative mortality, and survival rate are comparable with both lead systems; however, incorporating two defibrillating electrodes in one lead minimizes lead dislodgment and reduces implant time.

Temporal influences on the prediction of postinfarction mortality by heart rate variability: a comparison with the left ventricular ejection fraction

OBJECTIVE

To examine the influence of the duration of follow up on the values of heart rate variability (HRV) and the left ventricular ejection fraction (LVEF) for predicting mortality after infarction.

BACKGROUND

HRV is an index of autonomic balance that identifies patients at a high risk of arrhythmic events. The index is most depressed during the first few weeks after myocardial infarction whereas left ventricular function tends to deteriorate with time.

HYPOTHESIS

The value of depressed HRV measured before discharge from hospital for predicting mortality after infarction should decline with time.

METHODS

The HRV and the LVEF were assessed in 433 survivors of a first acute myocardial infarction: HRV < 20 units and LVEF < 40% were taken as cut off points. Kaplan-Meier survival functions for total cardiac mortality and sudden cardiac death were calculated for the whole five year follow up period and for different intervening periods.

RESULTS

During follow up of four weeks to five years there were 46 (10.6%) deaths and 15 (3.5%) patients died suddenly. Within the whole follow up period, HRV < 20 units and LVEF < 40% were both strongly associated with total cardiac mortality (p < 0.0001), but HRV was an independent predictor of total cardiac mortality only during the first six months of follow up. There were no deaths predicted by HRV < 20 units after the first year of follow up whereas LVEF < 40% had a sensitivity of 43% and a positive predictive accuracy of 9% for predicting death during this period. HRV < 20 units was better than LVEF < 40% in predicting sudden deaths during the first year of follow up but was an independent predictor only of those sudden deaths occurring within six months of infarction.

CONCLUSIONS

The duration of follow up affects the prediction of sudden death and total cardiac mortality from HRV. Reduced HRV as measured before discharge from hospital does not seem to retain independent prognostic value after six months of follow up. These findings have potential implications for the serial evaluation of HRV and for the prevention of sudden death after myocardial infarction.

Heart rate variability and its relation to ventricular arrhythmias in congestive heart failure

BACKGROUND

It has been shown that heart rate variability is decreased in patients with congestive heart failure and that depressed heart rate variability is associated with a propensity to ventricular arrhythmias. Little is known, however, about heart rate variability in patients with both congestive heart failure and ventricular arrhythmias.

METHODS

Spectral heart rate variability was analysed from 24 hour ambulatory electrocardiograms in 15 controls, 15 patients with non-sustained ventricular tachycardia associated with clinically normal hearts (NHVT group), and 40 patients with congestive heart failure (CHF group) secondary to either ischaemic heart disease (n = 15) or idiopathic dilated cardiomyopathy (n = 25). Of the 40 patients with congestive heart failure 15 had no appreciable ventricular arrhythmias (ventricular extrasystoles < 10 beats/h and no salvos) and formed the CHF-VA- group. Another 15 patients with congestive heart failure and non-sustained ventricular tachycardia formed the CHF-NSVT group.

RESULTS

Heart rate variability was significantly lower in the CHF group than in controls (mean (SD) total frequency 23 (12) v 43 (13) ms; low frequency 12 (8) v 28 (9) ms; high frequency 8 (5) v 14 (7) ms; p < 0.001). The differences in heart rate variability between controls and the NHVT group, between ischaemic heart disease and dilated cardiomyopathy, and between the CHF-VA- and CHF-NSVT groups were not significant. In the CHF group heart rate variability was significantly related to left ventricular ejection fraction but not associated with ventricular arrhythmias. The frequency of ventricular extrasystoles was significantly related to the high frequency component of heart rate variability (r = 0.54, p < 0.05) in the NHVT group. Stepwise multiple regression analysis showed that in the CHF group, heart rate variability was predominantly related to left ventricular ejection fraction (p < 0.05). There was no significant difference in heart rate variability between survivors (n = 34) and those who died suddenly (n = 6) at one year of follow up in the CHF group.

CONCLUSION

In patients with congestive heart failure, heart rate variability is significantly decreased. The depressed heart rate variability is principally related to the degree of left ventricular impairment and is independent of aetiology and the presence of ventricular arrhythmias. The data suggest that analysis of heart rate variability does not help the identification of patients with congestive heart failure at increased risk of sudden death.

QT interval dispersion in chronic heart failure and left ventricular hypertrophy: relation to autonomic nervous system and Holter tape abnormalities

OBJECTIVE

To study QT dispersion in left ventricular hypertrophy and chronic heart failure and to determine the relation to ventricular arrhythmias.

SETTING

Investigational laboratory of a tertiary referral centre.

STUDY DESIGN

Patients with left ventricular hypertrophy and normal systolic function (n = 14) and patients with chronic heart failure (n = 18) were matched with controls (n = 17). The QT dispersion was examined in relation to abnormalities in resting mechanical and autonomic function and to the findings of 24 hour Holter monitoring.

MAIN OUTCOME MEASURES

QT dispersion is the difference between the maximum and the minimum QT values from the 12 lead electrocardiogram. Mean(SD) QT dispersion from the 10 lead electrocardiogram was also examined once the 12 lead minimum and maximum values had been removed. The QT distribution is the curve describing the distance from the mean for all QT intervals (ms).

RESULTS

All measures of QT dispersion were increased significantly in left ventricular hypertrophy and tended to increase in those with heart failure. The QT distribution was abnormal in both heart failure and left ventricular hypertrophy. There was no relation between the degree of change in QT dispersion and the incidence of ventricular arrhythmia on 24 hour Holter monitoring. Also there was no relation between QT dispersion and autonomic or mechanical abnormalities. The QT dispersion was related to QRS duration.

CONCLUSION

Though QT dispersion and distribution are abnormal in left ventricular hypertrophy these findings do not support the hypothesis that QT dispersion reflects arrhythmic risk in either hypertrophy or heart failure.

Decreased heart rate variability in survivors of sudden cardiac death not associated with coronary artery disease

BACKGROUND

Although heart rate variability has already been studied in survivors of sudden cardiac death secondary to coronary artery disease, an assessment of heart rate variability in survivors of sudden cardiac death not associated with coronary artery disease has not been made.

METHODS

10 patients with aborted sudden cardiac death not associated with coronary artery disease (seven patients with primary ventricular fibrillation and three with unclassified mild cardiomyopathy) underwent two channel 24 hour Holter monitoring in a drug free state. All subjects were in sinus rhythm and had normal atrioventricular conduction and normal cardiac function. Spectral heart rate variability was analysed on a Holter analysis system and was expressed as total (0.01-1.00 Hz), low (0.04-0.15 Hz) and high (0.15-0.40 Hz) frequency components for each hour. Heart rate variability index was calculated for the 24 hour periods. 10 age and sex matched healthy subjects were taken as a control group.

RESULTS

The spectral heart rate variability over 24 hours was significantly lower in survivors of sudden cardiac death than in controls (total 38(15) v 48(14) ms; low, 25(11) v 32(13) ms; and high, 13(8) v 18(8) ms; p < 0.05 for all comparisons). The differences in the ratio of low/high (2.19(0.76) v 1.98(0.50), p = 0.132), mean heart rate (77(12) v 69(12) beats/min, p = 0.070), and heart rate variability index (38(12) v 44(16), p = 0.287) over 24 hours between survivors of sudden cardiac death and controls did not reach significance. Comparisons of the hourly heart rate variability over the 24 hour period between the two groups showed that the differences in all components of heart rate variability, low/high ratio and mean heart rate were highly significant. Furthermore, there was no significant difference in the maximum hourly heart rate variability over the 24 hour period. The minimum hourly heart rate variability was, however, significantly lower in survivors of sudden cardiac death than in controls (total, 20(8) v 28(4) ms; low, 12(6) v 17(3) ms; high, 6(2) v 8(2) ms; p < 0.05 for all comparisons).

CONCLUSIONS

These findings suggest that there is abnormal autonomic influence on the heart in patients without coronary artery disease at risk of sudden cardiac death. Hourly analysis of heart rate variability throughout the 24 hour period may provide additional information important in the identification of high risk patients.

Potentiation by ACE inhibitors of the dilator response to bradykinin in the coronary microcirculation: interaction at the receptor level

1. To examine the possibility that angiotensin-converting enzyme (ACE) inhibitors modulate the action of bradykinin at the receptor level, their effect on the dilator response to bradykinin was studied in the isolated saline-perfused heart of the rabbit. 2. Continuous infusion of bradykinin (10 nM) elicited a transient decrease in coronary perfusion pressure (CPP) and increased prostacyclin (PGI2) release which returned to baseline values within 30 min. 3. Subsequent co-infusion of ramiprilat (> or = 10 nM) or moexiprilat, but not of the less potent ACE inhibitor n-octyl-ramipril (RA-octyl), caused another fall in CPP and an increase in PGI2 release, the magnitude and time course of which were almost identical to the first response to bradykinin. No change in CPP or PGI2 release was observed when the ACE inhibitors were administered in the absence of exogenous bradykinin. 4. Infusion of D-Arg[Hyp3]-bradykinin (10 nM), a specific B2-receptor agonist which was significantly more resistant to degradation by ACE than bradykinin, produced virtually identical changes in CPP and PGI2 release when compared to bradykinin. Subsequent co-infusion of ramiprilat was similarly effective in restoring the fall in CPP and increase in PGI2 release elicited by D-Arg[Hyp3]-bradykinin as in the presence of bradykinin. 5. In concentrations which should block the degradation of bradykinin by ACE in the coronary vascular bed, two ACE substrates, hippuryl-L-histidyl-L-leucine (0.2 mM) and angiotensin I (0.3 microM), were unable to elicit a significant change in CPP or PGI2 release while ramiprilat and another ACE inhibitor, quinaprilat, were still active in the presence of these substrates. 6. To reveal the potential B2-receptor action of ramiprilat, its effect on the constrictor response to bradykinin was studied in the rabbit isolated jugular vein. Ramiprilat (0.1 MicroM), but not RA-octyl (1 MicroM),potentiated the endothelium-independent, B2-receptor-mediated constrictor response to bradykinin, but not that to the thromboxane-mimetic U46619 (9,11-dideoxy-ll alpha,9 alpha-epoxymethano-prostaglandin F2.).Moreover, ramiprilat but not RA-octyl caused a concentration-dependent, B2-receptor antagonist sensitive increase in tone when administered alone.7. These findings suggest that an interaction of ACE inhibitors with the B2-receptor or its signal transduction pathway rather than an accumulation of bradykinin within the vascular wall is responsible for the restoration of the endothelial response to bradykinin (dilatation, PGI2 release) in the coronary vascular bed of the rabbit.

Angiotensin-converting enzyme inhibitors in cardiovascular anesthesia

Besides the long-term regulation of extracellular fluid volume, the RAS plays an important physiologic role in maintaining venous return and blood pressure during acute hemodynamic stresses. ACE inhibitors may therefore alter venous return and cardiac output regulation during anesthesia and surgery. This may be regarded as a drawback of ACE inhibition when other factors interfere with cardiovascular homeostasis; deleterious hemodynamic events may therefore occur when blood volume is decreased, which may be frequent during cardiovascular anesthesia and surgery. However, the alternative solution should not be to stop ACE inhibitors preoperatively. This would allow recovery of RAS control of blood pressure, but at the expense of some regional circulations. From this point of view, preliminary results from early studies during cardiovascular anesthesia and surgery showing redistribution of regional blood flow with inhibition of ACE are encouraging; whether postoperative outcome can be improved deserves further studies. At this time, the evidence is that ACE inhibition does not allow the anesthesiologist to be tolerant of hypovolemia.

Multiple dose pharmacokinetics and concentration effect relationship of the orally active renin inhibitor remikiren (Ro 42-5892) in hypertensive patients

1 Three double-blind, randomized, placebo controlled, multiple oral dose studies in patients with mild to moderate hypertension were performed to study tolerability, pharmacodynamics and pharmacokinetics of remikiren. Doses of 100-800 mg remikiren or placebo were given over 8 days to altogether 144 patient volunteers. In some cases (n = 46) single i.v. doses of 100 mg were administered 4 h after the last oral dose. Plasma remikiren concentrations, plasma renin activity and immunoreactive renin concentrations were measured. Pharmacokinetic parameters were estimated using model independent techniques and the concentration-effect relationship was evaluated using population pharmacometric methods. 2 In most patients no distinct absorption and disposition phase could be identified, since plasma concentrations fluctuated widely over a period of approximately 10 h. Peak plasma concentrations (Cmax) were achieved within 0.25-2 h postdose. Mean Cmax values (on the first and last day of oral treatment) were in the magnitude of 4-6 ng ml(-1) (200 mg), 23-27 ng ml(-1) (300 mg), 65-83 ng ml(-1) (600 mg) and 47-48 ng ml(-1) (800 mg). Cmax and AUC0-t values were clearly different for different doses within single studies. Intersubject variability in pharmacokinetic parameters was much higher than intrasubject variability. No drug accumulation in plasma was apparent. 3 Inhibition of the angiotensin I production rate correlated well with plasma drug concentrations according to the Emax-model. An IC50 value of 0.5 ng ml(-1) (0.8 nM) was estimated. No correlation between blood pressure changes on the last day of oral treatment and either plasma remikiren concentrations or plasma renin inhibition was found.

New therapeutic agents in the management of hypertension: angiotensin II-receptor antagonists and renin inhibitors

OBJECTIVE

To review the chemistry, pharmacokinetics, and clinical trials of two new classes of antihypertensive drugs, angiotensin II-receptor antagonists and renin inhibitors.

DATA SOURCES

Primary literature on angiotensin II-receptor antagonists and renin inhibitors was identified through a comprehensive medical literature search from 1961 through 1993. This search included journal articles, abstracts, and reports of both animal and human research published in the English language. Indexing terms included renin-angiotensin aldosterone system, renin inhibitors, angiotensin II antagonists, DuP 753, losartan, MK954, A-64662, and Ro 42-5892.

STUDY SELECTIONS

Emphasis was placed on clinical and pharmacokinetic studies in humans for drugs that are currently in Phase I-III research protocols in the US.

DATA EXTRACTION

All available data from human studies were reviewed.

DATA SYNTHESIS

Angiotensin II-receptor antagonists and renin inhibitors may be effective antihypertensives with few adverse effects noted in the small studies completed. Their potential advantage over angiotensin-converting enzyme (ACE) inhibitors includes a possible smaller adverse effect profile. In the past, the clinical utility of angiotensin II-receptor antagonists and renin inhibitors has been limited because of poor oral bioavailability, although newer agents are more readily bioavailable.

CONCLUSIONS

Angiotensin II-receptor antagonists and renin inhibitors may be the next new classes of antihypertensives marketed. However, definitive conclusions about their roles in the management of hypertension are not possible until larger clinical trials assessing their efficacy and safety and comparing them with ACE inhibitors are completed.

The management of heart failure: a matter of definition?

The term heart failure has become a label for more than one clinical entity. For many years heart failure has been used to denote patients with various heart diseases who have begun to suffer from fluid retention, pulmonary venous hypertension, or systemic venous hypertension, either alone or in combination. More recently, the term heart failure has been applied to the combination of effort intolerance and reduced left ventricular contractility due to ischemic heart disease or other myocardial disease. Comparison of the results of epidemiological studies and therapeutic trials is complicated by variation in the composition of the patient populations selected for study. Drug treatment of heart failure remains fairly empirical. Distinction should be made between immediate or prognostic benefits related to the etiological diagnosis, and benefits related specifically to prevention and relief of, for example, fluid retention, rhythm disturbances, or ventricular hypertrophy. The response of individual patients to several forms of drug treatment, including digoxin, ACE inhibitors, and beta-blockade, is unpredictable. Prospective identification of patients liable to respond well to these drugs is not yet possible, but would greatly assist the choice of treatment. At present, trial of therapy is required in each patient to establish benefit and to avoid long-term treatment of nonresponders.

Haemodynamic and hormonal responses to oral enalapril in salt depleted normotensive man

A combination of dietary sodium restriction (40 mmol day-1) and frusemide pretreatment has been used to activate the renin angiotensin system (RAS) in order to characterise the haemodynamic and hormonal responses to enalapril in young normotensives. Enalapril significantly reduced supine blood pressure with a mean maximum fall of 19 +/- 7.6, compared with 6.5 +/- 6.8 mm Hg with placebo. Similar but greater responses were seen in erect blood pressure. Mean maximal plasma ACE inhibition (78 +/- 5.7%) was associated with a significant increase in PRA from 5.2 +/- 2.1 ngAI ml-1 h-1 to a peak of 29.1 +/- 6 ngAI ml-1 h-1. This simple well tolerated regimen produced consistent RAS activation and gave readily measurable falls in blood pressure following enalapril. This model may be used to undertake detailed assessments of ACE inhibition, renin inhibition and angiotensin receptor blockade.