Iliac artery patency before and immediately after percutaneous transluminal angioplasty: assessment with time-of-flight MR angiography

PURPOSE

To assess the efficacy of magnetic resonance (MR) angiography of iliac arteries before and immediately after percutaneous transluminal angioplasty (PTA).

MATERIALS AND METHODS

In 14 patients with 22 diseased iliac artery segments (external or common), axial two-dimensional time-of-flight MR angiography was performed. Images were reconstructed with a maximum-intensity-projection (MIP) algorithm. MR angiography was performed 1-4 days after diagnostic digital angiography and 6-24 hours after PTA. Findings obtained before and immediately after PTA were compared for number and location of significant (ie, > 50%) stenoses, length and diameter of balloon to be employed, and diameter of the stenotic artery after PTA. Linear regression analysis was performed.

RESULTS

Sensitivity and specificity of MR angiography for determination of significant stenoses were 95% and 97%, respectively. Before PTA, balloon dimensions depicted on MR angiograms and digital angiograms were well correlated (r = .76, P < .05). After PTA, MR angiograms and digital angiograms provided similar findings in all but one case.

CONCLUSION

MR angiography helped determine if PTA is indicated and depicted iliac artery patency after PTA.

Relationship between Rap1 protein phosphorylation and regulation of Ca2+ transport in platelets: a new approach

Although the interrelationship between the two messengers Ca2+ and cyclic AMP in platelet function is well documented, its mechanism of action still remains to be established. We investigated here the question of the regulation of platelet Ca(2+)-ATPases by cyclic AMP through the phosphorylation of the Rap1 protein using a pathological model. We first found experimental conditions where Ca(2+)-transport by platelet membrane vesicles appeared to be dependent on the phosphorylation of the Rap1 protein. Then, we studied platelets of patients with congestive heart failure for their expression of the potential 97 kDa Ca(2+)-ATPase target of regulation through the Rap1 protein as well as the phosphorylation of the Rap1 protein using the catalytic subunit of the cyclic AMP-dependent protein kinase (C. Sub.). In the first patients studied, we found no significant modification in the expression of the 97 kDa Ca(2+)-ATPase by Western blotting using the PL/IM 430 monoclonal antibody which specifically recognized this isoform. In contrast, the Rap1 protein was differentially phosphorylated when using 15 micrograms/ml of the C. Sub. These results allowed us to use these pathological platelets to study the relationship between the expression of Rap1 protein and the regulation of Ca2+ transport by selecting a patient with severe heart failure. We could show a decrease in the expression as well as in the phosphorylation of Rap1 protein and demonstrate a lower effect of C. Sub. on Ca2+ transport. Finally, by studying a further series of patients, we could confirm that the decrease in Rap1 protein expression in heart failure, whatever its extent, was variable, and could strictly correlate the expression of Rap1 protein with the stimulatory effect of C. Sub. on Ca2+ transport. Besides the evidence for regulation of the expression of the Rap1 protein in platelets from patients with heart failure, these findings constitute a new approach in favour of the regulation of platelet Ca2+ transport through the phosphorylation of the Rap1 protein.

[Classic treatment of chronic heart insufficiency. What if new?]

The aims of treatment of chronic heart failure are to improve the symptoms and the quality of life, reduce mortality and prevent left ventricular dysfunction. Before the first symptom occurs, neurohormonal activation takes place (increased catecholamines and atrial natriuretic peptide levels). Diuretics improve symptoms and are irreplaceable for the elimination of salt and water overload. Loop diuretics are used more often than the thiazides. Their deleterious effects on electrolyte balance are well known. The fact that they activate the renin angiotensin system is a more recent acquisition; the increase in plasma renin activity is a poor prognostic factor. Diuretics potentialize the vasodilator effect of angiotensin converting enzyme inhibitors which inhibit the neurohumoral activation induced by the diuretics. This therapeutic association is very logical, effective and allows reduction in the dosage of the diuretic. To date, there are no large scale controlled studies of the effects of diuretics on mortality. Spironolactone corrects hypokalaemia and hypomagnesaemia induced by loop diuretics. Moreover, it has been shown experimentally in renovascular hypertension and in hyperaldosteronism, that this molecule can prevent myocardial fibrosis, a factor which leads to ventricular dysfunction. The RALES study will analyse the effect of associating spironolactone to diuretic and ACE inhibitor therapy on the mortality of patients in NYHA classes III-IV. The value of digitalis in heart failure patients with sinus rhythm is a classical controversy. Digitalis has a positive inotropic effect (inhibition of NaK-dependent ATPase). More recently, a favourable neurohormonal effect has been reported; digitalis decreases the activation of the sympathetic and renin-angiotensin systems.(ABSTRACT TRUNCATED AT 250 WORDS)

[Baroreflexes and congestive heart failure]

Abnormal responses are found in the early stages of heart failure with increased sympathetic and decreased parasympathetic activity, causing peripheral arteriolar vasconstriction and tachycardia respectively. The cardiopulmonary baroreflex may be studied by decreasing venous return ("low body negative pressure") and by measuring vascular resistance forearm. The arterial baroreflex may be studied by changing aortic pressures (by intravenous phenylephrine or nitroglycerin). Orthostatism and the tilt test deactivate the cardiopulmonary and arterial baroreflexes simultaneously. These baroreflexes are impaired in patients with heart failure. Their activation does not cause the usual sympatho-inhibition so contributing to increased sympathetic tone. This dysfunction may result from a change at any point on the reflex pathway: the baroreceptors themselves, the afferent, central and efferent pathways. It is selective as during the cold pressor test, the vasoconstrictor response remains intact. One of the possible mechanisms of baroreflex dysfunction in heart failure is loss of sensitivities of the baroreceptors. This may be multifactorial: structural abnormalities, changes in compliance or functional abnormality. Even if the loss of sensitivity is partially related to a change in compliance, other factors play a role. It is more functional than structural abnormalities because, after cardiac transplantation, the baroreceptors regain their sensitivity within 2 to 3 weeks. Excessive Na-K dependent ATPase activation of the smooth muscle cells of the carotid sinus could lead to hyperpolarization of the cell membrane, so reducing the excitability of the receptor. Aldosterone is one of the factors which could activate the Na-K ATPase, as this hormone directly increases pump activity and favorizes the synthesis of new pumps in the vascular smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

[Incidence and prognosis of early primary cardiogenic shock in myocardial infarction]

The aim of this retrospective study was to analyse the results of coronary reperfusion on the incidence and short and medium term prognosis of early primary cardiogenic shock in acute myocardial infarction. Of 339 consecutive patients admitted within 6 hours of the onset of acute myocardial infarction, 25 (7.4%) had cardiogenic shock from the onset. The majority of patients (18) underwent direct angioplasty with a successful result in 16 cases. Intravenous thrombolysis was instituted in 5 cases followed by emergency coronary angiography leading to "rescue" coronary angioplasty in 3 cases, which was successful in 2 cases. Two patients had no coronary revascularisation because of a double contra-indication to thrombolysis and catheterization by the femoral approach. Intra-aortic balloon pumping was used in 17 cases. Complementary emergency surgical revascularization was necessary in 5 patients (20%). In all, early reperfusion of the infarct-related artery was obtained in 80% of cases (20 patients). The hospital mortality was 72% (18 patients) due to refractory cardiac failure in nearly all cases. After an average follow-up of 17 months, 3 of the 7 survivors of the hospital period have died and of the 4 remaining patients, 2 are in the NYHA classes III or IV. Recent therapeutic advances have not influenced the incidence of cardiogenic shock but have significantly increased the proportion of very early cardiogenic shock, whereas the late cardiogenic shocks of more progressive onset, have nearly disappeared (4/339, 1.2% in this series). The prognosis of these early shocks, caused by severe myocardial damage, remains catastrophic and hardly improved by emergency coronary reperfusion by angioplasty and intraaortic balloon pumping.(ABSTRACT TRUNCATED AT 250 WORDS)

[Difficulties in the diagnosis of cardiac insufficiency in octogenarians]

The incidence of heart failure in octogenarians is high and its diagnosis not always easy. In many cases it is made by excess or by omission. Obtaining a history is often difficult. Signs may be masked, false or indicative of another disease process. Dyspnea, edema of the lower limbs and crepitations are relatively non-specific. Jugular distension, tender hepatomegaly and a diastolic gallop are much more valuable. Diagnosis of the underlying etiology also raises problems. While hypertension is commonplace and easy to identify, ischemic heart disease is common and often missed. Tight aortic stenosis must be identified since its treatment is surgical. Hypertrophic cardiomyopathy is often an echocardiographic discovery. Post-embolic chronic cor pulmonale, or secondary to chronic obstructive lung disease, must always be considered in the presence of right heart failure without hypertension or chest pain. Appropriate treatment is dependent upon accurate diagnosis.

Eligibility for reperfusion therapy and outcome in elderly patients with acute myocardial infarction

Reperfusion therapy by thrombolysis or angioplasty was considered in 260 unselected patients consecutively admitted within 6 h of the onset of Q wave myocardial infarction. Rates of reperfusion and in-hospital mortality were compared in 206 patients < 70 years and 54 patients > or = 70 years. Early reperfusion was obtained in 86.4% of the patients under 70 years and in 72.2% of those over 70 (P < 0.01). Thrombolysis was more frequently used in the younger group (66.0% vs 31.5%, P < 10(-5)), and primary angioplasty in the older (44.4% vs 29.6%, P < 0.05). Overall in-hospital mortality was higher in the older group (22.2% vs 4.4%, P < 10(-5)). After successful reperfusion, mortality was 12.8% in the patients over 70 and 3.9% in those under 70. After failed or unproven reperfusion, mortality was 46.7% in the patients over 70 and 7.1% in those under 70. Reperfusion therapy is feasible in the majority of patients over 70 years, but failure to attempt or to achieve reperfusion is associated with a poor outcome. Although not controlled, this study provides an incentive for attempting early reperfusion therapy as often as possible in the elderly with acute myocardial infarction.

[Acute myocardial infarction in patients over 70 years of age]

Demographic changes in cardiovascular disease explain the marked increase in the number of myocardial infarctions affecting individuals aged over 70. The prognosis remains poor, with hospital mortality of the order of 30%. The reticence of physicians to use reperfusion techniques (intravenous thrombolysis and coronary angioplasty) is paradoxically considerable. Several studies have nevertheless shown that the benefit/risk ratio of such methods not only persists, but is increased in this age group, which should encourage the widening of their indications. Thorough evaluation of the best management strategy would require a randomised comparative trial, but angioplasty would probably ensure early reperfusion in a larger proportion of elderly patients than thrombolysis, because of the high incidence of contraindications to the latter as well as of cardiogenic shock in this age group.

Primary coronary angioplasty for acute myocardial infarction with contraindication to thrombolysis

Patients with acute myocardial infarction (AMI) and contraindication to thrombolysis have a high mortality and morbidity with conventional medical treatment. Among 226 consecutive patients hospitalized within 6 hours of the onset of Q-wave AMI, 45 (20%) had contraindications to thrombolysis. All were treated by emergent primary angioplasty. Mean age of the 45 patients was 60 +/- 11 years and 8 (18%) were > or = 70 years old; 17 (38%) had multivessel disease and 5 (11%) presented with cardiogenic shock. Successful angioplasty was achieved in 42 of the 45 patients (93%) 52 +/- 27 minutes after admission and 238 +/- 100 minutes after the onset of pain. Overall in-hospital mortality was 9% (4 of 45). Neither major bleeding nor stroke occurred. There was 1 case of early symptomatic reocclusion, treated with emergent repeat angioplasty without reinfarction. Predischarge angiography in 33 patients showed only 1 silent reocclusion (3%). Ejection fraction at discharge was 46 +/- 13%. Repeat catheterization at 6 months in 19 patients showed 4 restenoses (21%) and 4 reocclusions (21%) of the infarct-related artery. There were 3 late deaths (2 noncardiac), which gave survival rates of 87 and 85% at 1 and 3 years, respectively, and event-free survival rates of 71 and 69% including in-hospital deaths. There were no cases of late reinfarction. Consequently, in this series, primary coronary angioplasty proved safe and highly effective in rapidly restoring sustained infarct-vessel patency during AMI, and led to a greater improvement in early and late outcomes than that reported in the literature for medically treated subjects in this high-risk subset for which thrombolytic therapy is contraindicated.

Late thrombotic obstruction of an aortic bioprosthetic valve: successful treatment by oral anticoagulation

Thrombotic obstruction of aortic bioprostheses is rare. Few cases have been reported involving the use of the Carpentier-Edwards (CE) prosthesis, the Hancock bioprosthesis, or the Medtronic Intact porcine valve. Thrombolytic therapy for mechanical valve thrombosis has been used frequently even though it is known to carry a high risk of embolism and recurrence. However, the use of this therapy was reported for the first time only recently, in a case of acute aortic thrombosis which occurred 3 1/2 months after bioprosthesis insertion. We report a case of late progressive thrombotic obstruction of a CE aortic valve 3 years after insertion. The case was successfully treated with coumadin therapy, as confirmed by serial Doppler echocardiographic examinations and a 3-year follow-up.

[The clinician's view of restenosis: methodological and therapeutic aspects]

The study of restenosis after angioplasty poses serious methodological problems. The first is the definition of angiographic criteria of restenosis. These should be based on quantitative angiographic measurements in absolute values of coronary diameter rather than on the use of percentage stenosis which is an inaccurate indication of the true severity of the coronary disease. Moreover, the use of an arbitrary threshold > or = 50% stenosis at angiographic control tends to "pre-select" poor initial results of angioplasty as restenosis. Criteria based on absolute values of coronary artery diameter have enabled the demonstration of a close correlation between an excellent result of angioplasty and the degree of the restenosis 6 months later which suggests that a too good result of angioplasty may be related to increased intimal hyperplasia. This is a real dilemma for those performing angioplasty knowing that a mediocre initial result does not guarantee a good long-term result. In addition, it seems that the diameters of coronary arteries 6 months after angioplasty have a Gaussian distribution. This would imply that intimal hyperplasia is a constant phenomenon after angioplasty and that it is its degree which varies between patients with and without restenosis. Restenosis would therefore be more of a quantitative than a qualitative phenomenon. This justifies the use of continuous variables in the study of restenosis and a categorical approach would therefore be less valuable, not as powerful statistically and based on thresholds of an arbitrary nature. This could also explain the contradictory results concerning predictive factors of restenosis in the literature.(ABSTRACT TRUNCATED AT 250 WORDS)

[Ischemic cardiomyopathy: remodeling, hypertrophy, subendocardial risk. Can processes be controlled?]

Ischaemic cardiomyopathy reflects the myocardial dysfunction caused by coronary disease. It results from the association of 1. segmental infarction(s) responsible for ventricular "remodelling", i.e. expansion of the necrotic area(s) and hypertrophy-dilatation of the rest of the ventricle, eventually concurring to heart failure; 2. areas which are viable but with a function that is reversibly compromised by severe acute or chronic ischaemia (myocardial sideration or hibernation) affecting mainly the subendocardium. The spontaneous course of cardiomyopathy towards the worst can be arrested by 1. revascularisation of the myocardium at risk by coronary reperfusion performed either as an emergency in case of infarct in the process of formation, or after detection of the viable myocardial areas by isotopic methods; 2. prevention or limitation of ventricular remodelling by coronary reperfusion and improvement of the ventricular load by administration of angiotensin-converting enzyme inhibitors and nitroglycerin. The Survival and Ventricular Enlargement study (SAVE) has been the first to demonstrate the relationship between limitation of ventricular remodelling and improvement of the secondary prognosis of infarction obtained by angiotensin-converting enzyme inhibitors.

A patency-oriented strategy for early management of acute myocardial infarction using emergency coronary angiography and selective coronary angioplasty

From June 1988 to March 1991, an unselected cohort of 150 consecutive patients with acute myocardial infarction (AMI) (less than 6 hours) was managed according to a strategy designed to ensure early patency of the infarct-related artery in the maximum number of patients. The following procedures were used: (1) intravenous thrombolysis, which was the usual treatment (n = 103), followed in 98 cases by emergency coronary angiography 90 minutes after the beginning of thrombolysis. This identified 31 thrombolysis failures (32%) and led to 19 rescue angioplasties (18 successes). All patients were then scheduled for predischarge angiography. (2) Direct angioplasty, which was performed in 40 patients because of contraindications to thrombolysis (n = 23), cardiogenic shock (n = 3), diagnostic doubt (n = 7) or "ideal" conditions for direct angioplasty (n = 7). Success (defined as Thrombolysis in Myocardial Infarction [TIMI] flow greater than 1, with a residual stenosis less than 50% in the infarct-related artery) was achieved in 36 of 40 patients (90%). (3) The 7 remaining patients were given conventional medical treatment because of advanced age, contraindications to thrombolysis and angioplasty, or spontaneous reperfusion (confirmed by emergency angiography). In all, emergency angioplasty was performed in the acute phase in 39% of the 150 patients in this nonselected cohort.(ABSTRACT TRUNCATED AT 250 WORDS)

[Sudden death in heart failure. Analysis and prevention]

Sudden death is a frequent complication of heart failure occurring in 35 to 45 per cent of the cases. This multifactorial event may be of haemodynamic origin (acute heart failure, electro-mechanical dissociation) or, more often, of rhythmic origin (torsade de pointe, sustained ventricular tachycardia, ventricular fibrillation, bradycardia, asystole). Numerous structural, haemodynamic, metabolic, ionic, neurohormonal and iatrogenic factors facilitate ventricular hyperexcitability. The main predictive factors of sudden death in heart failure are the presence of coronary heart disease and of reduced left ventricular ejection fraction; the prognostic value of ventricular rhythm disorders is controverted. Prevention of sudden death begins with correcting those factors which facilitate disturbances in rhythm and conduction. Beta-blockers are effective in the post-infarction period, but there is no evidence that other drugs are useful. Identifying patients at high risk and determining the therapeutic approach that reduces this risk are still incompletely resolved problems.

[Disorders of diastolic function in chronic left ventricular insufficiency]

Abnormalities in the diastolic function of the left ventricular pump are the common determinant and, above all, the earliest manifestation of all forms of chronic left ventricular failure, whether or not the left ventricular systolic function is abnormal. Congestive signs, in particular, are directly related to abnormalities of ventricular filling. Primary diastolic dysfunction is the cause of left ventricular failure in about 40 p. 100 of the cases, but it may also be observed in almost all cardiopathies. In myocardial ischaemia the pressure-volume relation is displaced upwards owing to a slowed down, inhomogeneous and incomplete relaxation. Left ventricular hypertrophy, whether it is due to excessive pressure (arterial hypertension, aortic stenosis) or reflects a primary hypertrophic cardiomyopathy, is associated with a slowing down of ventricular relaxation and a reduction of left ventricular diastolic distensibility, even though the ventricular pump systolic function remains normal for a long time. Outside alterations in the distensibility of the ventricular muscle, ventricular dilatation alters ventricular filling by forcing the ventricle to function on the vertical part of its diastolic pressure-volume relation. Nowadays, the aged hearts is the most frequent cause of heart failure with normal systolic function. In all cases dysrhythmias and atrioventricular desynchronization act as aggravating factors. Treatment is often difficult since positively inotropic drugs or arterial vasodilators frequently have a modest or even deleterious effect.

[Converting enzyme inhibitors and cardiac insufficiency: current findings and perspectives]

Angiotensin-converting enzyme inhibitors are mixed vasodilators with a prolonged sustained effect in chronic heart failure. They also act on the reactivity of peripheral circulation, on ventricular remodelling after myocardial infarction, on myocardial hypertrophy in arterial hypertension and on ventricular hyperexcitability. They alleviate the symptoms of symptomatic heart failure, and they constitute the only treatment that has been able to improve the survival of patients with the most severe heart failure. Several studies are in progress to determine whether these drugs should be used as first-line therapy.

[Role of digitalis derivatives in the treatment of cardiac insufficiency with sinusal rhythm]

The value of digitalis in the treatment of heart failure with sinus rhythm remains controversial. It has been demonstrated that the moderate positively inotropic effect of digitalis observed after acute administration persists without tachyphylaxis. Digitalis produces symptomatic improvement, but its therapeutic quotient is low and its influence on mortality is unknown. This last point has become crucial, especially since some positively inotropic drugs increase ventricular rhythm disorders and are responsible for over-mortality among heart failure patients. In contrast, angiotensin-converting enzyme inhibitors reduce mortality in patients with severe heart failure. In short, digitalis is useful only in certain physiopathological types of heart failure where it is used electively and complements the action of angiotensin-converting enzyme inhibitors.

[Aorta-left ventricle coupling in permanent arterial hypertension using Doppler echocardiography]

We have studied 12 sustained hypertensive patients (H) (9 men and 3 women) untreated and without other heart disease than a left ventricular hypertrophy, 37 to 70 years of age (mean 56 +/- 12) and 12 normotensive subjects (N) of the same sex and 35 to 77 years of age (mean 52 +/- 16 ans). We have measured 1) arterial pressure (AP) by a standard mercury sphygmomanometer, 2) diameter of ascending aorta (AD), end diastolic left ventricular radius (r) and thickness (Th) by M mode echocardiography with 2D echo control., 3) isthmus-diaphragm pulse wave delay (PWD) from aortic velocity curves recorded in the isthmus and diaphragm aortic crossing by pulsed doppler. We derived 1) the pulse wave velocity (PWV) as PW = SL/PWD where SL is the sternal length, 2) PWV/AD ratio as an indirect index of characteristic impedance, 3) Th/r and LV mass (m) according to Teichholz formula: (table; see text) In both groups 1) m is significantly correlated with SAP (r = 0.67 p less than 0.001), PP (r = 0.61 p less than 0.001), PWV (r = 0.52 p less than 0.01) but not with PWV/AD; 2) Th/r ratio is significantly correlated with SAP (r = 0.64 p less than 0.001), PP (r = 0.63 p less than 0.001), PWV (r = 0.53 p less than 0.001) and PWV/AD (r = 0.41 p less than 0.05). Relationship between PWV and age of H is linear (r = 0.75 p less than 0.001) and shifted at left of that of N which is also linear (r = 0.061 p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

[Value of early vasodilator treatment with prazosin in chronic cardiac insufficiency]

The purpose of the present study was to find out whether the beneficial effect of prazosin in congestive heart failure persists after 2 and 6 months of treatment and whether the clinical and haemodynamic data obtained correlate with the response to treatment. Twenty-four patients of mean age 50.0 +/- 3.00 years presenting with congestive heart failure stage II (3 cases), stage III (18 cases) or stage IV (3 cases) in the NYHA functional classification were treated. All abstained from taking digitalis at least one week before treatment and were given prazosin 14.5 +/- 0.77 mg/day together with spironolactone 25 to 100 mg/day. The results of treatment were assessed by its effects on echocardiography, systolic time intervals, ejection fraction and cardiac index measured by the radioisotope method, and maximal duration of a 60-watt exercise on an ergometric bicycle. Treatment was discontinued before the 6th month in 9 out of 10 non-responders. The remaining 14 patients responded to treatment and their condition improved. Mean blood pressure rose in 6 months from 95.4 +/- 3.92 to 104 +/- 3.06 mmHg (p less than 0.05). The cardiothoracic ratio was reduced at 2 months (-0.05 +/- 0.01, p less than 0.01) and at 6 months (-0.08 +/- 0.02, p less than 0.01). Systolic time intervals were not significantly altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein and 28S ribosomal RNA fractional turnover rates in the rat heart after abdominal aortic stenosis

The rate of synthesis of myocardial proteins and ribosomal ribonucleic acid (rRNA) was measured during the development of cardiac hypertrophy in rats using a continuous intracardiac infusion of 14C-tyrosine and 3H-uridine in unanaesthetised animals. Cardiac overload was induced by abdominal aortic stenosis. Left ventricular weight and total myocardial RNA concentration were significantly increased on day 4 after aortic stenosis (+19% and +18% respectively). On day 8 left ventricular weight reached +52% whereas RNA concentration had not increased further (+13%). The fractional turnover rates were calculated using the specific activities of intracellular free tyrosine and free uracil nucleotides (precursors) and those of protein bound tyrosine and 28S rRNA bound uridine monophosphate (products) respectively. The fractional rate of synthesis of proteins and rRNA (expressed as percentage per day) increased from 24% to 45% for proteins and from 25% to 34% for rRNA and peaked by day 2. The RNA activity, expressed as gram of protein synthesised per day and per gram of total RNA, was unchanged on day 1 and reached a maximal value on day 2 (+107%). These results suggest that the pre-existing ribosomal RNA could be underutilized under control conditions and that the boosting of RNA transcription, associated with that of protein translation, is a complementary process rather than a prerequisite for the transition period leading to hypertrophy.

Screening of inotropic drugs on isolated rat and guinea pig hearts

A technique is described for screening the effects of inotropic drugs on isolated rat or guinea pig hearts perfused at constant coronary pressure and at a frequency of 6 Hz. Their performances, including function curves, were recorded using an intraventricular balloon. Both preparations became either sensitive from initially having been insensitive, or more sensitive from having been slightly sensitive at the outset, to inotropic interventions, provided the external calcium concentration was reduced to 0.25 mM for the rat and 0.50 mM for the guinea pig. The inotropic effect of drugs such as isoproterenol, forskolin, and theophylline was only slightly altered by lowering [Ca]o. Amrinone, sulmazole, and beta agonists such as xamoterol, cicloprolol, pindolol, or RU 42173 almost never caused an inotropic effect at the serum calcium concentration of 2.50 mM, whereas they did provoke a positive response at low [Ca]o. Other compounds such as ouabain, salbutamol, and pimobendan were toxic at high [Ca]o, although at reduced [Ca]o their positive effect on contractility was quite evident.