[Screening for high risk cardiac diseases in athletes]

The prevention of cardiovascular complications occurring during sporting activity requires detection of well-known pathologies which are often clinically latent but which may present with sudden death. The problem of detection and the recommendations and French laws concerning this subject are summarised in this article.

Management of heart failure in the elderly: recommendations from the French Society of Cardiology (SFC) and the French Society of Gerontology and Geriatrics (SFGG)

Heart failure, a frequent disease in the elderly, has a pejorative prognosis. Clinical diagnosis is complicated by atypical or difficult-to-interpret symptoms and by the concomitant presence of other diseases, particularly cognitive impairment, neurological disorders and diseases of the musculoskeletal system. Among the additional investigations, echocardiography remains underused. Impairment of diastolic left ventricular function is frequent. The usual laboratory tests must include calculation of the creatinine clearance, which is indispensable for dosage adjustment of certain drugs (ACE inhibitors, digoxin, spironolactone). The value of plasma natriuretic peptide assays as diagnostic tools has not been determined in elderly or very elderly populations and the plasma B-type natriuretic peptide increases with age. Comprehensive geriatric assessment is essential in order to screen for concomitant diseases and determine the patient's degree of dependence. The general objectives of treatment remain applicable to the elderly subject: improvement in the quality of life, reduction of mortality and the number and duration of hospitalisations, and slowing disease progression. In the frail elderly subject, symptom alleviation is to be the primary objective. In the absence of specific studies on elderly or very elderly subjects, most of the recommendations have been extrapolated from the data based on the evidence generated in younger populations. The dietary rules are to be more flexible than those used for younger subjects, particularly in order to prevent the risk of denutrition induced by strict salt-free diets. Special precautions for the use of heart failure drugs are due to comorbidities and the pharmacokinetic and pharmacodynamic changes related to aging. Drugs dosage increase is to be cautious and carefully monitored for adverse reactions. The therapeutic programmes in which multidisciplinary teams are involved reduce the number and duration of hospitalisations and the costs generated by the disease.

[Epidemiology and prognosis of cardiac insufficiency]

Cardiac insufficiency, the outcome in the majority of cardiac diseases, is common and serious. The frequency is rising, and the fatality, even if it has diminished thanks to various treatments, remains elevated. The epidemiology of cardiac insufficiency is relatively little known in France, despite its considerable economic impact on the health system, while this constraint is ever increasing. Some significant French statistics: the number of cardiac insufficiency cases is about 500,000, there are 120,000 new cases each year. The incidence rises from 4@1000 of males and 3@1000 of females aged between 55 and 64 years to 50@1000 of males and 85@1000 of females aged 85 to 94 years. The average age for occurrence of cardiac insufficiency is 73.5 years; two thirds of patients are over 70 years. There are about 3.5 million consultations and 150,000 hospitalizations for cardiac insufficiency every year. The average length of stay is 11 days. There are more than 32,000 deaths annually from cardiac insufficiency. The costs linked to cardiac insufficiency represent more than 1% of total medical costs. Cardiac insufficiency is a major problem for public health, and it is more and more so. This must prompt us to treat our patients better, and to undertake more preventive measures.

[Study of blood pressure, hemodynamic, ventilatory and metabolic responses to isometric exercise performed during dynamic exercise in health subjects]

The object of this study was to study the blood pressure, haemodynamic, ventilatory and metabolic changes on isometric exercise during a dynamic effort in healthy subjects. Twelve healthy subjects underwent isometric exercise by manual prehension at 40% maximal capacity under these conditions: isolated (A), five minutes after the onset of rectangular dynamic exercise on a cycle at 60% of ventilatory threshold (B) and at the fourth minute of the recovery phase of dynamic exercise (C). The blood pressure, heart rate, stroke volume and cardiac index measured by Doppler echocardiography, systemic arterial resistances, respiratory flow and respiratory rate, were measured before and after each isometric exercise. The results showed blood pressure and heart rate to increase in a similar manner during isometric exercise under all conditions. The cardiac index increased by 29.5% +/- 8.3% (p < 0.01) under condition A and by 38.1% +/- 10% (p < 0.01) under conditions C but did not change significantly under conditions B. On the other hand, the systemic arterial resistances increased by 15.5% +/- 6.5% (p < 0.05) under conditions B, decreased by 8.8% +/- 3.9% (p < 0.05) under conditions C but did not change significantly under conditions A. The respiratory flow increased under all three conditions although the respiratory rate was only increased under conditions B. The authors conclude that, in healthy subjects, the increase in blood pressure during isometric and dynamic exercise is the result of an increase in systemic resistances whereas, during isometric exercise, it is flow-dependant.

Opposite change with ischaemia in the antifibrillatory effects of class I and class IV antiarrhythmic drugs resulting from the alteration in ion transmembrane exchanges related to depolarization

It is known that class I antiarrhythmic drugs lose their antifibrillatory activity with severe ischaemia, whereas class IV antiarrhythmic drugs acquire such activity. Tachycardia, which is also a depolarizing factor, has recently been shown to give rise to an alteration of ion transmembrane exchanges which is particularly marked in the case of calcium. This leads one to wonder if the change in antifibrillatory activity of antiarrhythmic drugs caused by ischaemia depends on the same process. The change in antifibrillatory activity was studied in normal conditions ranging to those of severe ischaemia with a class I antiarrhythmic drug, flecainide (1.00 mg x kg(-1) plus 0.04 mg x kg(-1)x min(-1), a sodium channel blocker, and a class IV antiarrhythmic drug, verapamil (50 microg x kg(-1) plus 2 microg x kg(-1) x min(-1)), a calcium channel blocker. The experiments were performed in anaesthetized, open-chest pigs. The resulting blockade of each of these channels was assessed at the end of ischaemic periods of increasing duration (30, 60, 120, 180, 300, and 420 s) by determining the ventricular fibrillation threshold (VFT). VFT was determined by means of trains of diastolic stimuli of 100 ms duration delivered by a subepicardial electrode introduced into the myocardium (heart rate 180 beats per min). Ischaemia was induced by completely occluding the left anterior descending coronary artery. The monophasic action potential was recorded concurrently for the measurement of ventricular conduction time (VCT). The monophasic action potential duration (MAPD) varied with membrane polarization of the fibres. The blockade of sodium channels by flecainide, which normally raises VFT (7.0 +/- 0.4 to 13.8 +/- 0.8 mA, p < 0.001) and lengthens VCT (28 +/- 3 to 44 +/- 5 ms, p < 0.001), lost its effects in the course of ischaemia. This resulted in decreased counteraction of the ischaemia-induced fall of VFT and decreased aggravation of the ischaemia-induced lengthening of VCT. The blockade of calcium channels, which normally does not alter VFT (between 7.2 +/- 0.6 and 8.4 +/- 0.7 mA, n.s.) or VCT (between 30 +/- 2 and 34 +/- 3 ms, n.s.), slowed the ischaemia-induced fall of VFT. VFT required more time to reach 0 mA, thus delaying the onset of fibrillation. Membrane depolarization itself was opposed as the shortening of MAPD and the lengthening of VCT were also delayed. Consequently there is a progressive decrease in the role played by sodium channels during ischaemia in the rhythmic systolic depolarization of the ventricular fibres. This reduces or suppresses the ability of sodium channel blockers to act on excitability or conduction, and increases the role of calcium channel blockers in attenuating ischaemia-induced disorders.

[Evaluation of a specific French scale of activity in chronic heart failure. A national multicenter study. Group for Cardiac Insufficiency and Cardiomyopathy of the French Society of Cardiology]

Many systems have been proposed to evaluate the functional incapacity caused by chronic cardiac failure. The classification of the New York Heart Association (NYHA) is the best known. It is subjective, poorly reproducible and has a poor predictive value on effort. The authors propose a Specific French Scale of Activity with the object of a more accurate functional evaluation of cardiac failure, easier to use by the doctor and more specific to French patients and their life styles. A French multicentre study was set up in hospital departments by the French Society of Cardiology working group on Cardiomyopathy and Cardiac Failure to assess this new classification with respect to the NYHA classification and peak VO2 (Weber's classification). Eight centres participated in the study. A total of 124 patients with chronic cardiac failure and a mean age of 61 years (102 men) were included. Cardiac failure was due to ischaemic heart disease in 72 cases, hypertension in 10 cases, dilated cardiomyopathy in 40 cases and aortic regurgitation in 2 cases. Eighty-two patients underwent a double evaluation using the French Scale: 40 patients by 2 physicians and 42 patients by a physician and a nurse. Good reproducibility was found between the assessment by the 2 physicians in 35 cases (87%) and between the physician and nurse in 30 cases (71%). When compared with peak VO2, the classification was concordant in 47% of cases using the NYHA and in 61% of cases using the French Scale, with variation of one class in 40% of cases with the NYHA and 35% of cases with the French Scale. These results show good reproducibility and correspondence of classification with the exercise test which was better using the French Scale than the NYHA classification.

Efficacy of a beta-adrenergic receptor antagonist, propranolol, in preventing ischaemic ventricular fibrillation: dependence on heart rate and ischaemia duration

OBJECTIVES

To investigate the prevention of ventricular fibrillation with a beta-adrenergic receptor (beta-AR) antagonist in anaesthetized, open-chest pigs in a model of ischaemia, intended to reproduce what happens either in anginal attack or in the first hour of infarction.

METHODS

Ventricular fibrillation threshold (VFT) was determined with trains of diastolic stimuli of 100 ms duration delivered by a subepicardial electrode inserted in the area subjected to ischaemia. Ischaemia was obtained by the complete occlusion of the left anterior descending coronary artery, either near its origin during brief but increasing periods (30, 60, 90, 120, 150, 180, 240, 300 s), or half-way from its origin for a much longer time (more than 60 min).

RESULTS

During transient proximal occlusion and isoprenaline infusion (0.25 microgram/kg/min), propranolol (50 micrograms/kg plus 2 micrograms/kg/min) attenuated both tachycardia and the fall in VFT to 0 mA. The shortening of MAP duration accompanying depolarization of the fibres was concurrently slowed down, and time to fibrillation prolonged (122 +/- 15 to 262 +/- 14 s, p < 0.001). In the absence of isoprenaline infusion, propranolol exerted similar effects, but to a lesser degree, in proportion to heart rate dependent on sympathetic activity. In contrast, it became unable to raise VFT before and during ischaemia, when heart rate was kept constant by pacing. After persistent midportion occlusion, significant differences in VFT were found only at the 5th min, depending on whether heart rate was accelerated by isoprenaline (0.8 +/- 0.2 mA), left normal (1.8 +/- 0.3 mA) or slowed down by propranolol (1.6 +/- 0.3 mA). Later on, especially after 15 and 25 min of ischaemia, VFT, which was below 1.0 mA, did not appear to be influenced by the activation or blockade of beta-ARs: spontaneous fibrillations were observed in the same number in this period with or without the administration of propranolol. Beyond 30 min after occlusion, the rise in VFT, subsequent to the first irreversible cell damage, also occurred in the same way.

CONCLUSIONS

The prevention of ischaemic ventricular fibrillation by a beta-AR antagonist, judged from VFT, is easily checked experimentally when ischaemia is only transitory, especially if sympathetic activity is high. The maintenance of VFT at a relatively high level is essentially related to the depressant effect on the sinus rate. The same animal model does not give support to an effective protection in the first hour of infarction. However, the control of heart rate may also be beneficial in these circumstances by attenuating systemic haemodynamic disorders.

Prevention by calcium antagonists of profibrillatory effects of class I antiarrhythmic drugs in acute myocardial ischemia: study in pig heart in situ

Class I antiarrhythmic drugs do not decrease, but increase, the risk of ventricular fibrillation in the ischemic myocardium. On the contrary, vulnerability to fibrillation related to ischemia appears to be substantially reduced by calcium antagonists. We assessed whether the calcium antagonist diltiazem (0.50 mg/kg bolus plus 0.02 mg/kg/min infusion) could prevent the profibrillatory effect or even partially restore the antifibrillatory effect of a class I antiarrhythmic drug, flecainide (1 mg/kg bolus plus 0.04 mg/kg/min infusion) in the ischemic myocardium of anesthetized, open-chest pigs. Ischemia was obtained by completely occluding the left anterior descending coronary artery near its origin. Vulnerability to fibrillation was assessed by electrical fibrillation threshold (EFT), measured with diastolic impulses of 100 msec duration delivered at a rate of 180 beats/minute. Diltiazem did not oppose the rise in EFT induced by flecainide in the absence of ischemia (6.8 +/- 1.2 to 9.9 +/- 0.9 mA, p<0.001). It limited the fall in EFT observed under the dual influence of ischemia and flecainide (4.2 +/- 0.9 vs 1.3 +/- 0.6 mA, p<0.001). By reducing calcium entry into myocardial fibers, diltiazem delayed ischemic depolarization, as evidenced by reduced shortening of the monophasic action potential duration from 215 +/- 7 to 200 +/- 4 msec, instead of 178 +/- 6 (p<0.001), and reduced lengthening of intraventricular conduction time from 33 +/- 5 to 43 +/- 4 msec, instead of 53 +/- 4 (p<0.01). Therefore, diltiazem is likely to prevent the loss and even the reversal of the antifibrillatory properties of flecainide due to myocardial ischemia in dosages that do not adversely affect myocardial contractility or atrioventricular conduction to a large extent.

Magnesium--a profibrillatory or antifibrillatory drug depending on plasma concentration, heart rate and myocardial perfusion

BACKGROUND

The opinions on the efficacy of magnesium as an antiarrhythmic drug vary considerably. The action of magnesium on vulnerability to fibrillation was therefore investigated in anaesthetized, open-chest pigs under different conditions as regards plasma concentration, heart rate and myocardial perfusion.

METHODS

Vulnerability to fibrillation was assessed by electrical fibrillation threshold (EFT), measured with 100-ms duration diastolic impulses. These stimuli were delivered to the heart normally perfused, at a usual (90 and 120 beats/min) or accelerated (180 beats/min) rate. Vulnerability to fibrillation was also assessed at the high rate (180 beats/min) in the heart made ischaemic by complete occlusion of the left anterior descending coronary artery near its origin. EFT was then measured at the end of occlusion periods which were of increasing duration (30, 60, 90, 120 s). Monophasic action potential (MAP) duration, intraventricular conduction time, left ventricular dP/dt max (LVdP/dt max) and mean blood pressure were concurrently measured.

RESULTS

In the absence of ischaemia, 5 mumol.kg-1.min-1 magnesium i.v. infusion, which raised plasma concentration to 1.78 +/- 0.14 mmol/L, lowered EFT, measured at the rate of 116 beats/min, from 14.0 +/- 1.1 to 6.8 +/- 1.0 mA (P < 0.001), without significant variation of the other parameters. Administered as previously or in a markedly higher dose (400 mumol.kg-1 loading dose and 10 mumol.kg-1.min-1 infusion) which raised plasma concentration up to 4.84 +/- 0.52 mmol/L, magnesium significantly influenced neither EFT nor MAP duration, reduced by the high rate (180 beats/min) to 6.2-6.7 mA and 212-220 ms respectively. Under the same conditions, at the same 180 beats/min rate, ischaemia brings about a fall of EFT, from 6.9 down to nearly 0 mA, with occurrence of fibrillation, in approximately 120 s. Magnesium failed to slow this fall and to delay the onset of fibrillation. In contrast, within the minutes following the end of occlusion, magnesium increased EFT to a great extent (from 7.1 +/- 0.4 to 13.5 +/- 0.7 mA, P < 0.001), with a significant prolongation of MAP duration (212 +/- 6 to 234 +/- 8 ms, P < 0.01).

CONCLUSION

Magnesium may develop profibrillatory or antifibrillatory effects depending on plasma concentration, heart rate and myocardial perfusion.

Calcium antagonists and prevention of ventricular fibrillation induced by transient or persistent ischemia

Experimental studies have shown the limitation by calcium antagonists of the propensity to fibrillation secondary to the occlusion of a large coronary artery. However, this capacity, studied in the acute phase of infarction, is less obvious and still under debate. Ischemia was therefore produced in anesthetized, open-chest pigs by complete occlusion of the left anterior descending coronary artery according to two modes, either near its origin during brief but increasing periods (30, 60, 120, 180 s, etc) or half-way from this origin for a much longer time (60 min). The time course of vulnerability to fibrillation was monitored by ventricular fibrillation threshold (VFT), measured by trains of diastolic stimuli of 100 ms. Verapamil was administered in a 50 micrograms/kg dose followed by 2 micrograms/kg/min infusion. 1) In the case of brief proximal occlusions under pacing at a constant high rate (180 beats/min), verapamil slowed the decline of VFT from 6-8 mA to nearly 0 mA. VFT was 4.4 +/- 0.4 mA after 60 s ischemia, whereas it had already fallen to 1.8 +/- 0.3 mA (p < 0.001) in the absence of the drug. Accordingly, the onset of spontaneous fibrillation which depends on the decrease in VFT to about 0 mA was prolonged from 2-3 to 6-9 min. Bradycardia, concurrently produced by verapamil, is a factor which enhances these alterations. 2) In the case of a persistent midportion occlusion of the artery under sinus rate, fibrillations were similarly delayed by verapamil from 14-25 to 23-49 min after occlusion, but they were more numerous. VFT was lowered to critical values later, but also for a longer time. The period propitious to fibrillation was prolonged because the return of VFT to higher values reflecting hypoexcitability subsequent to the first cell injury was substantially delayed. Consequently, calcium antagonists should often prevent ventricular fibrillation when transient ischemia disappears before VFT falls to the vicinity of 0 mA. In contrast, a real benefit could not be expected from these drugs when ischemia is persistent since they then only delay fibrillations, the number of which is increased.

Ischaemia-induced loss or reversal of the effects of the class I antiarrhythmic drugs on vulnerability to fibrillation

1. In the last decade, a number of clinical observations have questioned the efficacy of certain class I antiarrhythmic drugs against ischaemia-induced ventricular fibrillation. The effects of three drugs of this class, disopyramide (Ia), lignocaine (Ib) and flecainide (Ic) on the vulnerability to fibrillation during experimental ischaemia were investigated. 2. The study was carried out in anaesthetized, open-chest pigs (n = 8 for each of the drugs, in addition to the control group, n = 6). Vulnerability to fibrillation was evaluated by measuring electrical fibrillation threshold (EFT) by means of stepwise increased intensity of wide (100 ms) diastolic impulses applied to the ischaemic tissue at a 180 beats min-1 rate. Monophasic action potential (MAP) duration and conduction time in the ischaemic region were also measured. 3. EFT determinations were performed before and during periods of ischaemia induced by complete occlusion of the left anterior descending coronary artery near its origin. Ischaemic periods of increasing duration (30, 60, 90, 120, 150 s) were induced to determine the electrophysiological changes, of EFT especially, leading to fibrillation. 4. In the absence of ischaemia, all three drugs, administered by intravenous route (1 mg kg-1 plus 0.04 mg kg-1 min-1) increased EFT to a similar extent (from approximately 7 to 10 mA), despite a 25% prolongation of conduction time. 5. During ischaemia, none of the drugs prevented the fall in EFT towards 0 mA, resulting in spontaneous fibrillation. After 30 s of ischaemia, they no longer had any capacity for raising EFT and, after 60, 90 and 120 s of ischaemia, the decrease in EFT was exacerbated. This accelerated reduction in EFT shortened the time to onset of fibrillation (after 120 s of ischaemia, 62.5% of fibrillations with flecainide instead of 12.5 under control conditions, 75% instead of 25 with lignocaine and 50% instead of 25 with disopyramide). The reduction in MAP duration due to ischaemia was also significantly accelerated (at 60 s, 178 +/- 5 ms instead of 192 +/- 4 with flecainide, 175 +/- 3 ms instead of 194 +/- 5 with lignocaine and 180 +/- 5 ms instead of 196 +/- 3 with disopyramide) and the slowing of conduction was made worse (prolongation of conduction time by 70% instead of 50). 6. In conclusion, the antifibrillatory properties normally manifested by these drugs are first suppressed, then inverted by ischaemia, depending on oxygen debt varying with severity and duration of ischaemia.

Cardiac beta-adrenoreceptor activation and ventricular fibrillation under normal and ischemic conditions

OBJECTIVES

To investigate the role of ventricular and atrial beta-adrenoceptor activation by isoprenaline in the genesis of rhythm disorders and risk of fibrillation in the healthy or ischaemic heart.

METHODS

The study was performed in anaesthetized, open-chest pigs. Electrical fibrillation threshold (EFT) of the ventricles was measured with trains of diastolic stimuli of 100 ms duration synchronized with respect to the R-waves and delivered to the myocardium by a subepicardial electrode introduced into the area which could be subjected to ischaemia. Monophasic action potential (MAP) and effective refractory period (ERP) were recorded in the same area. Ischaemia was obtained by complete occlusion of the left anterior descending coronary artery near its origin during increasing periods (30, 60, 90, 120, 150, 180, 240 s).

RESULTS

At a rate varying according to the action exerted by isoprenaline on the sinus rate, EFT decreased by about 30% in the healthy heart during the infusion of 0.5 micrograms/kg/min isoprenaline under the influence of the acceleration of cardiac beats. In the ischaemic heart, sinus tachycardia accelerated the fall in EFT and the reduction in MAP duration and resulted sooner in spontaneous ventricular fibrillation. During ventricular pacing at a constant rate of 200 beats/min, isoprenaline raised EFT by nearly 80% in the absence of ischaemia, but this rise was abolished by ischaemia, at least of no-flow type.

CONCLUSION

Tachycardia produced by activation of atrial adrenoceptors decreases EFT in the healthy heart and aggravates its fall in the ischaemic heart. Ventricular adrenoceptor activation counteracts the EFT fall related to tachycardia in the healthy heart, but not in the ischaemic heart. Therefore, the protection against ischaemic fibrillation due to beta-blockers would be essentially attributable to their action on the sinus nodes.

Possible prevention by amlodipine of ventricular fibrillation related to brief ischemia episodes

Calcium antagonists may reduce propensity to ventricular fibrillation, by altering the balance between coronary blood flow and metabolic demand, and thus may substantially prolong time to occurrence of fibrillations. This delay in the onset of fibrillation should be sufficient to prevent sudden death in the case of transitory episodes of myocardial ischemia. Therefore, this study was based on the determination of time to onset of fibrillation in an animal model of transitory ischemia. This model was achieved by the complete, but transitory occlusion of the left anterior descending coronary artery near its origin under ventricular pacing at a constant high rate (180 beats/min), in anesthetized, open-chest pigs. Amlodipine was preferred to another calcium antagonist for this study because it is among the least negatively inotropic of these drugs. It was intravenously infused at 0.02 mg.kg-1.min-1. Time to fibrillation was prolonged from 87 +/- 10 to 146 +/- 16 s (p < 0.05) with the 0.30 mg/kg dose and to 201 +/- 22 s (p < 0.05) with the 0.60 mg/kg dose, without serious impairment of blood pressure or left ventricular dP/dtmax in the absence of ischemia. Concurrently, amlodipine significantly limited the shortening of monophasic action potential duration (200 +/- 4 vs. 172 +/- 6 ms), the lengthening of conduction time (43 +/- 2 vs. 53 +/- 2 ms), and the alterations of ST segments and T waves induced by 60 s ischemic depolarization. Consequently, amlodipine might reduce the incidence of sudden death by lengthening time to onset of fibrillation beyond the duration of the ischemia, when transitory.

[Apical hypertrophic cardiomyopathy]

Apical hypertrophic cardiomyopathy was defined initially by three electrocardiographic and angiographic criteria: the presence of giant (over 10 mm) inverted T waves in leads V4 and V5 of the resting ECG; an "ace of spades" appearance of left ventricular angiography in end diastole in the right anterior oblique projection; the electrocardiographic sum RV5 + SV1 greater than 35 mm. There after, authentic cases of apical hypertrophy have been demonstrated by imaging techniques or observed anatomically without the presence of these three criteria. The authors review the epidemiological, clinical and paraclinical features of this particular form of hypertrophic cardiomyopathy.

Delay by a calcium antagonist, amlodipine, of the onset of primary ventricular fibrillation in myocardial ischemia

Calcium antagonists have been reported to counteract the increase by ischemia of vulnerability to ventricular fibrillation. This ability might be especially of interest in the prevention of sudden death subsequent to a major, but transitory, inadequacy between myocardial oxygen requirements and available coronary blood flow produced by exercise, emotion, etc., because death is then not related to irreversible damage of myocardial fibers. This study has been undertaken to examine the protective effect of a calcium antagonist on an animal model of this type of ischemia. This model used complete, but transient occlusion of the left anterior descending coronary artery near its origin during pacing at a constant high rate (180 beats/min) in anesthetized, open-chest pigs, most often resulting in fibrillation within 1-2 minutes after a progressive fall of the electrical fibrillation threshold. Amlodipine was the preferred calcium antagonist for this study because it is only moderately negatively inotropic. The results of the preventive administration of amlodipine was assessed by the time to onset of fibrillation. Amlodipine 0.30 mg/kg prolonged this time by 50-100% (p < 0.05) without appreciable impairment of blood pressure or myocardial contractility. Concurrently, amlodipine delayed the shortening of the monophasic action potential duration, the lengthening of conduction time, and the alterations of ST segments and T waves linked to ischemic depolarization. Consequently, when given experimentally before the occurrence of major, but transitory ischemia, amlodipine protected against fibrillation. Similarly, in clinical settings it ought to delay sudden death that may occur as a result of a major but transitory inadequacy between myocardial oxygen requirements and available coronary blood flow.

Change of a beneficial effect into an untoward effect by ischaemia: effect of quinidine-like drugs on vulnerability to ventricular fibrillation

The effects of three quinidine-like drugs, disopyramide, lidocaine and flecainide were investigated in anaesthetized, open-chest pigs on vulnerability to ventricular fibrillation under normal conditions and under myocardial ischaemia conditions. Vulnerability to fibrillation was evaluated by electrical ventricular fibrillation threshold (VFT), measured with 100 ms duration diastolic impulses the intensity of which was increased by steps of 1.0 or 0.5 mA. Impulses were delivered at the rate of 180 beats · min(-1). The ventricles were subjected to pacing at the same rate before the VFT determination, particularly throughout periods of ischaemia of increasing duration (30, 60, 90, 120, 150 s), separated by appropriate intervals for reproducibility of the results. Monophasic action potential (MAP) duration and conduction time were monitored in the ischaemic area under pacing. Ischaemia was obtained by complete occlusion of the left anterior descending coronary artery near its origin. The three drugs were i.v. administered in clinical dose range (1.00 mg · kg(-1) plus 0.04 mg · kg(-1) · min(-1)). In the absence of ischaemia, they increased almost equally VFT (from about 7 to 10 mA), despite 25% prolongation of conduction time. But, none of them was able to impede the increasingly marked fall of VFT caused by ischaemia: at 30 s, they had already lost any capacity for raising VFT and, beyond this time, they even aggravated its fall which led to spontaneous fibrillation when VFT approached 0 mA. The faster fall of VFT shortened time to onset of fibrillation (20 24 fibrillations for the three drugs at 150 s as against 12 24 in control period), the ischaemia-induced reduction of MAP duration (by 20%) being also hastened and slowing of conduction enhanced, given the addition of the depressant effects of ischaemia and drugs on conduction. Consequently, the antifibrillatory properties normally manifested by the studied drugs are first suppressed, then inverted by ischaemia.

Disappearance with ischaemic depolarization of the antifibrillatory activity in a sodium channel blocker and appearance in calcium channel blocker

Results obtained in the prevention of ventricular fibrillation secondary to myocardial ischaemia are unexpected. Profibrillatory properties might be manifested by Class I antiarrhythmic drugs, normally antifibrillatory. Clear antifibrillatory properties might be manifested by calcium channel blockers, the antifibrillatory effects of which are normally questionable. Therefore, the action of a Class I antiarrhythmic drug, flecainide, and of a calcium channel blocker, verapamil, on the vulnerability to ischaemic ventricular fibrillation was assessed in anaesthetized, open-chest pigs by ventricular fibrillation threshold. Ventricular fibrillation threshold was determined with trains of diastolic stimuli of 100 msec duration, delivered at a rate of 180 beats/min (near that of the ventricular tachycardia), by a subepicardial electrode inserted into the area that could be subjected to ischaemia. Before determining this threshold, ventricles were paced at the same rate, particularly during the ischaemic periods. Ischaemia was produced by complete occlusion of the left anterior descending coronary artery, either at its origin or half-way from it, over increasing periods. The monophasic action potential and conduction time were recorded in the ischaemic area. Before ischaemia, flecainide was adapted to rais the ventricular fibrillation threshold, in spite of a lengthening of the conduction time. Verapamil was devoid of any influence on these parameters. The antifibrillatory effect of flecainide disappeared with ischaemia, which reduced the ventricular fibrillation threshold down to near 0 mA, with triggering of the spontaneous fibrillation at this level: this reduction was no longer counteracted and even hastened by flecainide, becomes finally profibrillatory. Verapamil, on the contrary, delayed the fall in ventricular fibrillation threshold, maintained far from 0 mA, with prevention of fibrillation, unless the occlusion was maintained over a much longer period. Verapamil similarly delayed the shortening of the monophasic action potential duration and the lengthening of the conduction time, preceding fibrillation and leading to it. Consequently, ischaemic depolarization is apparently responsible for the loss of antifibrillatory activity in a sodium blocker, such as flecainide, and the development of antifibrillatory activity in a calcium blocker, since the sodium channel is activated only at high potentials, whereas the calcium channel is activated at lower potentials.

[Value of calcium channel blockers in the prevention of ventricular fibrillation of ischemic etiology: experimental arguments]

The prevention of ventricular fibrillation raises a special problem when related to myocardial ischaemia, since class I antiarrhythmic drugs are then ineffective and may even behave as profibrillatory agents: the usual antifibrillatory properties of these drugs which are inhibitors of sodium channel, activated at high potentials, disappear with the disappearance of the role of sodium channel caused by ischaemic depolarization. Calcium channel then replacing sodium channel, calcium channel inhibitors should tend to prevent ischaemic ventricular fibrillation. Therefore, vulnerability to ventricular fibrillation was assessed in open-chest pigs by the threshold for fibrillation electrically induced with impulses of 100 ms duration at the rate of 180 beats/min. Ischaemia was produced by total occlusion of the left anterior descending coronary artery near its origin. Electrical fibrillation threshold was measured at the end of ischaemic period of increasing duration (30, 60, 120, 180, 240, 360 s) under control conditions and after i.v. administration of verapamil (50 micrograms/kg loading dose and 2 micrograms/kg/min infusion). Unaffected by verapamil when coronary circulation was normal, fibrillation threshold was raised by the drug when lowered by ischaemia, increasingly with the prolongation of ischaemia responsible for depolarization of the fibres, up to 500%. The rise of fibrillation threshold resulted in a delay in the triggering of fibrillation which occurs when the fibrillation threshold (6-8 mA) falls down to the pacing threshold (0.3-0.4 mA). These experiments tend to confirm the positive results recently obtained in man with verapamil in the prevention of postinfarction sudden death, provided that myocardial contractility is not too much adversely affected. But, in these experiments, left ventricular dP/dt max was not reduced by more than 15%, even just after the loading dose and returned to its control values within a few minutes.

Preconditioning reduces infarct size but accelerates time to ventricular fibrillation in ischemic pig heart

Preconditioning protects the rat heart from ventricular arrhythmias. However, the mechanism of this beneficial effect and its existence in large animal models remain unknown. We submitted 49 pigs to 40 min of left anterior descending coronary occlusion and 2 h of reperfusion and assessed the incidence of ventricular fibrillation (VF) and time to VF. Monophasic action potential duration (MAPD) and ventricular fibrillation threshold (VFT) were measured throughout the experiment. Preconditioning significantly reduced infarct size but failed to reduce the incidence of VF either during the 40-min ischemic insult or the following reperfusion. Moreover, preconditioning accelerated the onset of VF during the prolonged ischemia; time to VF averaged 8 +/- 2 min in the preconditioned group vs. 18 +/- 2 min in the control group (P < 0.05). This premature peak of VF in preconditioned hearts was associated with a significant decrease of VFT and shortening of MAPD. This suggests that preconditioning does not limit the incidence of VF in the pig model. Rather, preconditioning decreases the time to VF in this species, likely through lowering of the VFT and shortening of the action potential duration.

Profibrillatory effects of lidocaine in the acutely ischemic porcine heart

Because recent clinical studies have failed to show evidence of the benefit of lidocaine in the arrhythmias occurring in the early stage of myocardial infarction and have even shown an increased mortality in patients thus treated, we investigated the value of lidocaine as a protective agent against ventricular fibrillation related to myocardial ischemia in the in situ heart of anesthetized open-chest pigs subjected to transient total occlusion of the proximal left anterior descending coronary artery (LAD) under ventricular pacing at a constant high rate. Vulnerability to the fibrillatory process induced by coronary occlusion was assessed both by time to onset of ventricular fibrillation (TF) and by electrical ventricular fibrillation threshold (EFT) determined after coronary occlusions of increasing duration (30, 60, 120, 180 s). Monophasic action potential (MAP) was recorded concurrently in the nonischemic and ischemic areas. Lidocaine, even in relatively high doses (2-4 mg.kg-1), did not prolong TF, nor did it increase EFT. On the contrary, TF was significantly shortened and EFT was significantly decreased (15-30%) at the maximal concentrations of lidocaine, with return to control values in 40-60 min. Therefore, lidocaine tends to increase the risk of ischemic ventricular fibrillation (VF): It fails to control the extreme enhancement of excitability and worsens conduction disorders, even though it decreases normal conduction only slightly. Use of lidocaine against rhythm disorders in acute myocardial infarction (AMI), is at least debatable and probably contraindicated.

Bupivacaine hastens the ischemia-induced decrease of the electrical ventricular fibrillation threshold

Myocardial ischemia sensitizes the cardiotoxic effects of bupivacaine, especially the propensity to ventricular fibrillation. To investigate this sensitization and to elucidate its mechanism, the influence of bupivacaine alone, or associated with ischemia, was studied on electrical fibrillation threshold in anesthetized, open chest pigs. Determination of fibrillation threshold was performed with impulses of 100 ms duration at the rate of 180 bpm, in the absence of ischemia and at the end of increasing periods of ischemia (30, 60, 120, 180 s) obtained by complete occlusion of the left anterior descending coronary artery close to its origin. The effect of bupivacaine (1.00 mg/kg initial dose plus 0.04 mg.kg-1.min-1 over 25 min) was compared to the control in the same animals. This effect corresponded to 1.4-1.8 micrograms/mL plasma concentrations likely to be observed in humans after regional anesthesia. Bupivacaine significantly increased the fibrillation threshold before coronary occlusion from approximately 7.0 to 9.5 mA. In contrast, during ischemia the fibrillation threshold was shifted to the left and down, with a hastening of spontaneous fibrillation. Recording of monophasic action potentials in the ischemic area revealed that conduction time was prolonged by more than 100% under the combined influence of ischemia and bupivacaine, whereas the major enhancement of excitability due to ischemia was not attenuated by bupivacine. Therefore, bupivacaine should be used with caution in the condition of ischemia, especially if heart rate is rapid. In the present experiments, tachycardia is another factor in the enhancement of bupivacaine effects on conduction.

[Demonstration of the fibrillatory effect of class I anti-arrhythmia agents based on the time of fibrillation onset and electrical threshold in myocardial ischemia]

In recent clinical studies, certain class I antiarrhythmic drugs (flecaïnide, lidocaïne) appeared to be responsible for an increase in mortality, when used to treat ventricular arrhythmias occurring after or during infarction. Experimentally, in pigs whose rate of ventricular beats was kept constant by pacing, all the studied class I antiarrhythmic drugs, disopyramide, lidocaïne and flecaïnide, proved to be to a variable degree capable of shortening time to onset of fibrillation (TOF) elicited by controlled myocardial ischemia. Fibrillation occurred at the end of the decline, under the influence of ischemia, of electrical fibrillation threshold (EFT) down to near 0 mA. The fall of EFT to this level was checked by ischemias of increasing duration to be hastened by the cited antiarrhythmic drugs. In other words, these drugs exert a profibrillatory effect in the ischemic heart.

Can anaerobic threshold be used as an end-point for therapeutic trials in heart failure? Lessons from a multicentre randomized placebo-controlled trial. The VO2 French Study Group

Anaerobic threshold (AT), proposed as a non-invasive index of exercise tolerance, independent of patient motivation, is considered more reliable than exercise duration in assessing the effect of drug therapy in chronic heart failure (CHF). However, inter-observer variation in patients may be more difficult than in normal subjects. In a multicentre study, 85 patients from 10 centres performed a total of 331 bicycle maximal tests (ramp protocols, 10 watts.min-1) with respiratory gas analysis by different systems. A central committee reviewed all the tests. Percentages of AT determination ranged from 34% to 71% depending on the method used. Apart from the respiratory exchange ratio (RER) method, which yielded the lowest rate of determination: 34%, and the crossing point (when RER = 1), which yielded the highest rate, 71%, other methods of determination, such as carbon dioxide (42%), minute ventilation (52%) or ventilatory equivalents plotted vs time (57%), did not differ in the rate of AT determination. Thus, even among trained physicians, AT determination was not reliable. The crossing point may nevertheless be a valuable index from a pragmatic standpoint, although it occurs after the actual AT. Peak oxygen uptake should remain the main end-point in assessment of exercise capacity.

[Informed consent, what information is left after a therapeutic trial?]

In order to evaluate the outcome of information given to patients included in a therapeutic trial after having signed a consent form, 77 patients (68 men, 9 women with an average age of 57.9 years) included in the IMPACT study (multicenter, randomised, double-blind protocol, the main objective of which was to assess the antiarrhythmic effect of oral administration of delayed action mexiletine in patients with a recent myocardial infarction), answered a questionnaire of 85 items. The quantity and degree of comprehension of the recalled information at the end of the trial were appreciated from the replies to 13 questions based on the definition or understanding of the most important details of the consent form and on a comprehension score with a maximum value of 14 points. The global quantity of information recalled after an interval ranging from 5 to 21 months was estimated at 60% of the information provided but the recall was not uniform according to the different elements of the consent form: the aim of the study, the concept of placebo, the nature of the active treatment, the randomisation and possible side effects were only correctly apprehended by 40 to 50% of patients: the type of patient included, the duration of the trial, the content of the gelules, the division between treatment/placebo and the concept of double-blind were known to 50 to 75% of participants: the sites of the test centres, the possibility of unmasking the "blind" are of withdrawing from the trial were correctly understood in 75 to 90% of cases. The global average comprehension score was 8.7.(ABSTRACT TRUNCATED AT 250 WORDS)

Peak oxygen uptake during exercise in mitral stenosis with sinus rhythm or atrial fibrillation: lack of correlation with valve area. A study in 70 patients

Although the haemodynamic response during submaximal supine exercise in mitral stenosis has been well described, the determinants of peak oxygen uptake during maximal upright exercise are poorly characterized and may differ in sinus rhythm and atrial fibrillation. Seventy patients with isolated mitral stenosis underwent Doppler-echocardiography and bicycle exercise with respiratory gas analysis. Forty-two patients were in sinus rhythm (Group I) and 28 in atrial fibrillation (Group II). Peak oxygen uptake was 21.3 +/- 5.6 ml.min-1.kg-1 in group I and 18.1 +/- 5.1 ml.min-1.kg-1 in group II (P < 0.05). There was no significant correlation between indices of exercise tolerance (exercise duration, ventilatory threshold, peak oxygen uptake, indexed peak oxygen uptake, peak oxygen pulse) and valve area or gradient in either group. Indexed peak oxygen uptake was not correlated to delta oxygen pulse but was linearly related (r = 0.43) to delta heart rate (delta heart rate = peak heart rate/rest heart rate) in Group I but not in Group II. Thus, in patients with mitral stenosis, no correlation was found between the mitral valve area or the gradient at rest and maximal upright exercise tolerance, suggesting that peripheral adaptation and, in sinus rhythm, chronotropic reserve, are important compensatory mechanisms.

Vulnerability to ventricular fibrillation related to ischaemia: comparison of the acute effects of beta-blockers and calcium antagonists

A comparative evaluation of beta-blockers and calcium antagonists as protective agents against ventricular fibrillation related to myocardial ischaemia, was attempted in the pig heart in situ of anaesthetized, open-chest animals, subjected to a temporary complete occlusion of the left anterior descending coronary artery near its origin. This occlusion resulted in fibrillation occurring after a time depending on the vulnerability to the fibrillatory process. As this time to onset of fibrillation does normally not exceed a few minutes, its determination could be achieved repeatedly in the course of an experiment, in the absence and presence of drugs such as beta-blockers and calcium antagonists. When propranolol (0.05 mg/kg, i.v.) and verapamil (0.05 mg/kg, i.v.) abolished tachycardia produced by isoproterenol (0.25 micrograms/kg/min), the triggering of fibrillation was delayed in either case: in animals under atrial pacing at a rate close to the sinus rate on each determination, time to fibrillation was prolonged from about 160 to 400 sec by propranolol and from 160 to 640 sec by verapamil, with a return to control values within 60 min. Under ventricular pacing at a constant high rate (180 beats/min), no change was observed in time to fibrillation after propranolol (0.025 or 0.050 mg/kg), whereas verapamil, in the same conditions and in the same doses, multiplied this time by about 4 and 6, respectively. Consequently, propranolol and verapamil are likely to protect against fibrillation immediately after i.v. injection, but the protection due to propranolol is only indirect and a consequence of bradycardia which tends to increase the polarization of the muscular fibres, whereas verapamil adds to the same influence a direct preventive action by avoiding a cellular calcium overload in these fibres, which is responsible for the depolarization and fluctuations of their membrane potential.

Attenuation of the ischaemia-induced fall of electrical ventricular fibrillation threshold by a calcium antagonist, diltiazem

Calcium antagonists have been reported to decrease the incidence of sudden death in postinfarction management and vulnerability to fibrillation secondary to experimental coronary occlusion. In order to confirm such beneficial results regarding ischaemic ventricular fibrillation, the threshold intensity for fibrillation electrically induced with impulses of 100 ms and 180 beats.min-1 was measured during the course of ischaemias obtained by total occlusion of the left anterior descending coronary artery near its origin in open-chest pigs. The variations of electrical fibrillation threshold with ischaemia duration (30, 60, 120, 180, 240, 360 s) were compared under control conditions and after i.v. diltiazem (0.50 mg.kg-1 plus 0.02 mg.kg-1.min-1 over 25 min). Electrical fibrillation threshold was not influenced by diltiazem before, but raised during ischaemia, particularly from the 60th s (1.7 to 4.0 mA), with delay in the triggering of fibrillation which occurs when the fibrillation threshold falls down to the pacing threshold (0.2 to 0.3 mA). In 6 pigs out of 8, fibrillation was even avoided in the longest of the ischaemic periods considered (360 s), for fibrillation threshold ceased falling before reaching the critical level. These experimental results obtained with diltiazem are consistent with the clinical effectiveness of calcium antagonists recently observed in the prevention of postinfarction sudden death, provided that myocardial contractility is not too much adversely affected. But, left ventricular dP/dtmax was not reduced by more than 6.8% in the present experiments.

[Comparative study of different classes of anti-arrhythmia agents on the vulnerability of ischemic ventricular fibrillation]

A comparative study of the various classes of antiarrhythmic drugs as agents protecting against ischaemia-induced ventricular fibrillation was undertaken in the pig in situ heart, in anaesthetized animals which were subjected to complete temporary occlusion of the left anterior descending coronary artery. This occlusion resulted in fibrillation after a time which varied in inverse ratio to vulnerability to fibrillation. However, as this time did not exceed a few minutes, time to onset of fibrillation could be repeatedly measured in the course of an experiment, in the absence or in the presence of an antiarrhythmic drug. Under ventricular pacing at a constant rate, 180 beats/min, all the class I antiarrhythmic drugs, flecainide, disopyramide and lidocaine, in clinical dose range, reduced time to fibrillation to a large extent (25 to 50%) at the maximum of their action, with gradual return to control values within less than one hour. The enhancement of vulnerability to fibrillation was accompanied by reduction in intraventricular conduction velocity and fibrillation rate. With the same ventricular pacing, no change was observed in time to fibrillation under the influence of propranolol or amiodarone. As for verapamil, it lengthened this time considerably, up to 600%. However, bradycardia produced in usual circumstances ensures a real protection against ischaemic fibrillation with propranolol and amiodarone and enhances protection directly exerted by verapamil.

Arrhythmogenicity of antiarrhythmic drugs and intraventricular conduction disorders: possible aggravation by myocardial ischemia--study in the porcine in situ heart

The effects of three antiarrhythmic drugs were investigated in anesthetized, open-chest pigs, in a left ventricular area, under pacing at a constant high rate (180 beats/min), in the absence and presence of ischemia. Ischemia was produced by transient complete occlusion of the left anterior descending coronary artery near its origin. In addition to the surface electrocardiogram, conduction time and monophasic action potential were recorded in the contractile fibers. In the absence of ischemia, intravenous flecainide and propafenone 2.5 mg/kg, and intravenous cibenzoline 2.0 mg/kg considerably lengthened conduction time (by 50-90%) but had no significant effect on the monophasic action potential duration. Consequently, the cited antiarrhythmic drugs enhance the prolongation of conduction time by 60% but do not limit the 30% shortening of the monophasic action potential caused by ischemia. Contrary to what was expected, they largely reduced the time to onset of the fibrillation due to ischemia from about 120 to 25 seconds. Thus, they manifested profibrillatory properties (more pronounced than those of other antiarrhythmic drugs of class I), which might be explained by their potent action on depolarization.

[Efficacy and tolerability of isoptine LP in mild to moderate hypertension. A multicenter study with 50 patients]

A multicenter open trial involving 50 hypertension patients enabled evaluation of the efficacy and tolerability of Isoptine L.P. (sustained release verapamil) in mild to moderate essential hypertension. Following a 2-week placebo run-in period, patients were given Isoptine L.P. (240 mg/24 h) as a morning dose for 3 months, with a possible dose increase (360 mg/24 h) in case of diastolic blood pressure of 95 mmHg or more at the 30-day evaluation. Blood pressure was measured by mercury sphygmomanometer and, in 20 patients, by a Dinamap type Automatic device. After 3 months of treatment, blood pressure levels in supine and standing position, measured manually and automatically, showed a highly significant decrease, with a mean fall of 18.4 mmHg for systolic (13.7 percent) and 13.2 mmHg diastolic (-14.6 percent). 67 percent of patients were responders after 1 month of treatment and 79 percent at 3 months, including one-fifth at the dose of 360 mg/24 h. Seventeen patients, i.e. 34 percent, reported one or more adverse reactions. Among these, four patients had to stop treatment, twice because of headache and twice for constipation. Adverse events seen most frequently were constipation, headache, tiredness and vomiting. No cardiac adverse events were reported with the exception of one case of atrial premature contractions. The electrocardiogram revealed significant slowing of heart rate, as well as slight prolongation of PR and QT intervals and slight widening of the QRS complex. Tolerability on the basis of laboratory parameters was good.

Role of asynchronous activation of the ventricular fibres by an ectopic pacemaker in the accidents, especially fibrillation, caused by Ic antiarrhythmic drugs

Class Ic antiarrhythmic drugs, which are known to slow down conduction in the ventricular muscle, are likely to impair synchrony in activity of the ventricular fibres. Asynchronous activation was first investigated between an ischaemic and a normal area by the simultaneous recording in anaesthetized, open-chest pigs of two left ventricular monophasic action potentials (MAPs) under ventricular pacing at a high rate of 180 beats.min-1. Asynchronous activation was then investigated in the intact myocardium according to the distance separating the recording from the pacing electrode. Furthermore, mechanical effects of left ventricular systole were observed by recording dP/dt(max) and mean arterial blood pressure during the pacing periods. Ischaemia was produced by transient complete occlusion of the left anterior descending coronary artery near its origin; as a result, activation time reached 85 ms in the ischaemic area under flecainide administered iv in a 2.5 mg.kg-1 dose instead of approximately 60 ms in the normal area for fibres equi-distant from the pacing electrode. Similar delays in activation were observed in the intact myocardium, depending on whether the explored region was close to or far from the pacing electrode. In the latter case, the difference in activation time may become markedly greater if the distance or the dose of flecainide are increased. This difference, which possibly exceeds one-third of the MAP duration (practically unchanged by flecainide), may account for the occurrence of fibrillation or the sudden loss of systole mechanical efficacy.

Calcium channel modulators and susceptibility to ischaemic ventricular fibrillation: modification of cellular calcium overload

The effects of the calcium channel modulators, Bay k 8644, infused i.v. at a rate of 2.5 micrograms/kg/min, and diltiazem, injected i.v. in a dose of 0.5 mg/kg, on the susceptibility to fibrillation induced by ischaemia, were investigated in anaesthetized, open-chest pigs. Ischaemia was produced, under ventricular pacing at constant high rate (180 beats/min), by transient complete occlusion of the left anterior descending coronary artery, near its origin. It was maintained till the triggering of fibrillation. The propensity to fibrillation was judged from the time elapsing between the onset of occlusion and the onset of fibrillation (time to fibrillation). In addition to the surface electrocardiogram, conduction time and monophasic action potential were recorded in the ventricular contractile fibres, as were dP/dtmax in the left ventricle and blood pressure in the carotid artery. At the end of a 10 min infusion, Bay k 8644 lowered to a large extent (about 40%) the time to fibrillation, which returned to its control values within the following 20 min. Conversely, diltiazem increased the time to fibrillation by a factor 4 or 5 at 5 min after its administration. This time to fibrillation remained substantially increased 25 min later. These changes were not associated with alterations in conduction time or monophasic action potential duration in the absence of ischaemia, but with significant alterations in myocardial contractility and blood pressure: in the direction of an increase with Bay k 8644 and of a decrease with diltiazem. These results are in agreement with the enhancement by Bay k 8644 and the prevention by diltiazem of cell calcium overload which is at present recognized as being the essential determinant of the fibrillatory process.

Multicentre study of the determination of peak oxygen uptake and ventilatory threshold during bicycle exercise in chronic heart failure. Comparison of graphical methods, interobserver variability and influence of the exercise protocol. The VO2 French Study Group

Assessment of the ventilatory threshold (VT) has been proposed to assess exercise tolerance more objectively, particularly in clinical trials, but reproducibility, interobserver variability and feasibility of the graphical methods for determination of VT have not been properly studied in patients with chronic heart failure (CHF). Fifty-one patients with mild to moderate CHF (mean peak oxygen uptake (VO2): 20.5 ml.min-1.kg-1) were assessed during two consecutive bicycle exercise tests within 8 days. Two graded exercise protocols were compared with stages of 30 W every 3 min (22 patients) or 10 W/min (29 patients). VT was determined separately by five trained physicians using five different graphical methods. The 'crossing method' (first crossing of the VCO2 and VO2 curves) yielded the highest rate of determination (88%) but tended to overestimate the mean VT. The VE method (disproportionate increase of ventilation relative to VO2) produced the best interobserver agreement (coefficient of variation = 78%). Peak VO2 was very highly reproducible in both exercise protocols (relative difference 2-test 1/test 1 = -0.32% for the 30 W 3 min protocol; +2.18% for the 10 W.min-1 protocol). The reproducibility of VT was slightly lower regardless of the graphical method used to determine it (relative differences varied from -3.3% to +7.3%). Therefore, peak VO2 appears more suitable than VT for assessment of exercise tolerance in CHF.

Class Ic antiarrhythmic drugs and myocardial ischaemia: study in the pig heart in situ

The effects of three Ic antiarrhythmic drugs, flecainide, propafenone and cibenzoline, were investigated in anaesthetized, open-chest pigs, in a left ventricular area, during pacing at a constant high rate (180 beats min-1), in the absence and the presence of ischaemia. Ischaemia was produced by transient complete occlusion of the left anterior descending coronary artery 1-1.5 cm from its origin. In addition to surface electrocardiogram, conduction time and monophasic action potential were recorded in the contractile fibres. Measurement of the effective refractory period was added in the absence of ischaemia. In this event, flecainide and propafenone, each in a dose of 2.5 mg kg-1 i.v. and cibenzoline, 2.0 mg kg-1, i.v., considerably lengthened (by 50-90%) conduction time, but did not affect or hardly affected the duration of the monophasic action potential or the effective refractory period. Thus, it seems that these Ic antiarrhythmic drugs enhance the prolongation of conduction time by 60% and do not prevent the 30% shortening of monophasic action potential caused by ischaemia: contrary to expectation, they produced a large reduction (from about 120 to 25 s) in the onset time of fibrillation due to ischaemia. Thus, they manifested profibrillatory properties (more pronounced than those of other class I antiarrhythmic drugs), which might be explained by their potent action on depolarization with almost total absence of action on repolarization.

[Arrhythmogenic risk of antiarrhythmic drugs: study with class Ic drugs during myocardial ischemia]

The effects of three Ic antiarrhythmic drugs were investigated in anaesthetized, open-chest pigs, in a left ventricular area under pacing at constant high (180/min) rate, outside and during an ischaemia produced by temporary complete occlusion of the left anterior descending coronary artery, 1-1.5 cm from its origin. In addition to surface ECG, conduction time and monophasic action potential were recorded in the contractile fibres. Measurement of effective refractory period was added outside the periods of ischaemia. In this event, flecainide and propafenone, in 2.5 mg/kg dose, and cibenzoline, in 2.0 mg/kg dose, i.v. injected, lengthened considerably (50 to 90%) conduction time, but did not affect or hardly affected monophasic action potential and effective refractory period. During ischaemia, they did not hinder the abbreviation of monophasic action potential (30%) and reduced to a large extent (about 120 to 25 s) the onset time of fibrillation. The profibrillatory effect of Ic antiarrhythmic drugs, certainly more pronounced than those of other antiarrhythmic drugs, might be explained by their potent action on depolarization of the contractile fibres coincident with an almost total absence of action on repolarization.

[Chronic hemolysis and mitral insufficiency after surgical mitral valvuloplasty. Treatment by valve replacement, a case report]

The authors report a case featuring a chronic increase in lactic dehydrogenase (LHD) levels, 8 years after surgical mitral valvuloplasty with residual mitral regurgitation. This increase in LDH levels was the sign of chronic haemolysis and disappeared after valve replacement with a mechanical prosthesis. This rare complication was attributed to contact between the sutures and the teflon used for mitral valvuloplasty and turbulence created by the mitral regurgitation.

Ventricular and atrial electrophysiological effects of a IC antiarrhythmic drug, cibenzoline, in the innervated dog heart. Role of sodium and calcium channels

The effects of cibenzoline, rightly known as a sodium channel inhibitor (class IC antiarrhythmic drug), were investigated in anaesthetized, closed-chest dogs, on conduction in the contractile fibres, ventricular and atrial, the His-Purkinje system and the atrioventricular node. In ventricular muscle, conduction time was measured between base and apex by two endocavitary electrodes. The other conduction times were obtained from the recording of the His bundle potentials. In addition, effective refractory period was determined by the extrastimulus method in ventricular and atrial muscle and in the atrioventricular node, and sinus rate monitored in the intervals of pacing periods. In the absence of vagal tone, cibenzoline in 4 mg.kg-1 dose prolonged conduction times in the ventricular contractile tissue, His-Purkinje system and atrial contractile tissue to a large extent, but decreasingly from the former to the latter. This prolongation was antagonized by hypernatremia (174 mmol.l-1). In contrast, conduction time in the atrioventricular node, effective refractory periods and sinus rate were very little influenced. In the presence of vagal tone, the prolongation of conduction times in the ventricular contractile tissue. His-Purkinje system and atrial contractile tissue did not differ substantially from previously. It was the same for ventricular effective refractory period. But atrial effective refractory period was then considerably lengthened, while conduction time and effective refractory period in the atrioventricular node were greatly shortened and sinus rate notably accelerated.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of isoproterenol and propranolol on pharmacologically induced depression of intraventricular conduction

The cardiac adrenergic system is known to have practically no influence on conduction velocity in the ventricles under normal conditions. The effects of isoproterenol and propranolol were investigated on depression of intraventricular conduction induced by a class IC antiarrhythmic drug, cibenzoline, in anaesthetized, closed-chest dogs. In addition to electrocardiogram for measurement of QRS duration in sinus rhythm, conduction time was measured in the ventricular contractile tissue between an electrode advanced to the apex and a pacing electrode near the base, at 400- and 200-ms pacing periods. Effective refractory period (ERP) was measured concurrently according to the extrastimulus method. After intraventricular conduction had been slowed down by cibenzoline IV administered (loading dose of 3 mg/kg plus infusion of 0.2 mg/kg/min over 15 min), isoproterenol was infused or propranolol injected by the intravenous route also (0.5 mn/micrograms/kg/min over 5 min and 0.4 mg/kg, respectively). When conduction time has been raised by 75/150% (depending on the pacing rate), isoproterenol appears to attenuate and propranolol to aggravate substantially the impairment of conduction, whereas the reduction undergone by ERP does not differ from usual. Thus, reentrant arrhythmias might be prevented by isoproterenol and triggered by propranolol. Intraventricular conduction, when depressed, therefore, is sensitive to adrenergic drugs, probably because of the enhanced influence of polarization of the fibres in the presence of a sodium conductance impairment.

Biphasic dose-response relationship observed with Bay k 8644 on atrioventricular nodal conduction inhibited by verapamil

The effects of a calcium channel blocker, verapamil, on the atrioventricular (AV) node, are antagonized by calcium, intravenously infused, so long as plasma calcium concentration does not reach 5.0 or 5.5 mmol.l-1, as previously shown. Beyond this, the antagonistic effects decrease progressively, so that there is a bell-shaped relationship between dose (or concentration) and response. The purpose of the present experiments has been to investigate a possible similar dose-response curve with a calcium channel activator, Bay k 8644. The study was carried out in anaesthetized, atropinized dogs, with cardiac pacing. The His bundle potentials were recorded by endocavitary electrodes and the AV nodal effective refractory period was measured by the extrastimulus method. Verapamil impaired AV nodal conduction and additional infusion of Bay k 8644 at a rate of 1 microgram.kg-1.min-1 partly antagonized this effect. Increasing the infusion rate of Bay k 8644 to 5 micrograms.kg-1.min-1 did not further increase but reduced the antagonism. In other experiments where infusion of calcium had partly antagonized the effect of verapamil, Bay k 8644 infused after cessation of calcium infusion did not further antagonize the effect of verapamil which even became again increasingly marked. Consequently, in the AV node depressed by a calcium channel blocker, Bay k 8644 gives rise to a bell-shaped dose-response relationship of its verapamil-antagonistic action and the reversal of this action by high doses of Bay k 8644 can be observed after both administration of either calcium or Bay k 8644 in moderate doses.

Frequency- and time-dependent depression of ventricular distal conduction by two novel antiarrhythmic drugs, cibenzoline and flecainide

The effects of two novel antiarrhythmic drugs, cibenzoline and flecainide, known to exert potent inhibitory effects on sodium channel, were investigated on intraventricular conduction in anaesthetized, closed-chest dogs. During this study, in which the heart was electrically stimulated, the pacing period was gradually reduced in the 500-200 msec range, and the pacing rate was abruptly altered (2 sec) or sustained (8 to 10 sec) in order to study the possible frequency- and time-dependency of the depression of conduction. In addition to the electrocardiogram, the conduction time was recorded in the ventricular contractile tissue between an electrode advanced to the apex and the pacing electrode positioned near the base. Effective refractory period (ERP) was concurrently measured according to the extrastimulus method, and the monophasic action potential (MAP) recorded. The drugs were infused at a rate of 0.2 mg/kg/min over a 10 min period after a 4.0 mg/kg loading dose. Conduction time was lengthened by approximately 50% at low frequencies and 100% at high frequencies. Widening of the ORS complexes paralleled this lengthening, whereas the drugs tended only to prolong ERP, without preventing its shortening induced by acceleration. Cardiac disorders were aggravated when high pacing rates were maintained for 8 to 10 sec.

Coronary-to-bronchial artery anastomosis complicated with myocardial infarction

A patient with bronchiectasis had an inferolateral myocardial infarction. Coronary arteriography revealed a large anastomosis from the left circumflex artery to the left lower lobe bronchial arteries. The relationship between the patient's myocardial infarction and possible "coronary steal" is discussed.

Role of calcium in the rate-dependent depression of atrioventricular nodal conduction in the dog heart under vagal influence

Increase in heart rate may be detrimental to atrioventricular conduction. The effects of such an increase were investigated in the paced intact dog heart, by measuring the conduction time in the atrioventricular node (obtained from the His bundle potential recording) and the effective refractory period in this node as determined by the extrastimulus method. Investigations on atrioventricular nodal conduction were performed with and without vagal influence. After central restoration of vagal tone by dextromoramide in anesthetized animals, both parameters appeared to lengthen as the heart rate rose. This lengthening became considerable at the highest rates. After blockade of cholinergic receptors by atropine, no significant change occurred when the heart rate was raised. The prolongation observed under vagal tone was enhanced by the rise in the plasma calcium concentration to 3.10 mmol X l-1 and reduced by a calcium influx inhibitor, verapamil, in 0.2 mg X kg-1 dose. These effects are related to the calcium intracellular concentration, since the rise in this concentration beyond an optimum has been demonstrated to inhibit the calcium and potassium channel.