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J C Tardif

Publications and source records attributed to J C Tardif.

At least 19 recordsLinked to original sources
PubMed2004

A method for matching the refractive index and kinematic viscosity of a blood analog for flow visualization in hydraulic cardiovascular models.

In this work, we propose a simple method to simultaneously match the refractive index and kinematic viscosity of a circulating blood analog in hydraulic models for optical flow measurement techniques (PIV, PMFV, LDA, and LIF). The method is based on the determination of the volumetric proportions and temperature at which two transparent miscible liquids should be mixed to reproduce the targeted fluid characteristics. The temperature dependence models are a linear relation for the refractive index and an Arrhenius relation for the dynamic viscosity of each liquid. Then the dynamic viscosity of the mixture is represented with a Grunberg-Nissan model of type 1. Experimental tests for acrylic and blood viscosity were found to be in very good agreement with the targeted values (measured refractive index of 1.486 and kinematic viscosity of 3.454 milli-m2/s with targeted values of 1.47 and 3.300 milli-m2/s).

Biomechanical Phenomena↗
PubMed2003

Intravascular ultrasound of the elastic pulmonary arteries: a new approach for the evaluation of primary pulmonary hypertension.

OBJECTIVE: To assess the structural and functional characteristics of pulmonary arteries by intravascular ultrasound (IVUS) in the setting of primary pulmonary hypertension, and to correlate the ultrasound findings with haemodynamic variables and mortality at follow up. DESIGN: Prospective observational study. SETTING: University hospital (tertiary referral centre). PATIENTS: 20 consecutive patients with primary pulmonary hypertension (16 female; mean (SD) age, 39 (14) years). METHODS: Cardiac catheterisation and simultaneous IVUS of pulmonary artery branches at baseline and after infusion of epoprostenol. RESULTS: 33 pulmonary arteries with a mean diameter of 3.91 (0.80) mm were imaged, and wall thickening was observed in all cases, 64% being eccentric. Mean wall thickness was 0.37 (0.13) mm, percentage wall area 31.0 (9.3)%, pulsatility 14.6 (4.8)%, and pulmonary/elastic strain index 449 (174) mm Hg. No correlation was observed between IVUS findings and haemodynamic variables. Epoprostenol infusion increased pulsatility by 53% and decreased the pulmonary/elastic strain index by 41% (p = 0.0001), irrespective of haemodynamic changes. At 18 (12) months follow up, nine patients had died. A reduced pulsatility and an increased pulmonary/elastic strain index were associated with increased mortality at follow up (12.0 (4.4)% v 16.4 (4.4)%, p = 0.03; 369 (67) v 546 (216) mm Hg, p = 0.02). CONCLUSIONS: IVUS demonstrated pulmonary artery wall abnormalities in all patients with primary pulmonary hypertension, mostly eccentric. The severity of the changes did not correlate with haemodynamic variables, and epoprostenol improved pulmonary vessel stiffness. There was an association between impaired pulmonary artery functional state as determined by IVUS and mortality at follow up.

Adolescent↗
PubMed2001

Pulsatile hemodynamics in congestive heart failure.

Pulse pressure, an indirect measure of vascular stiffness and pulsatile load, predicts clinical events in congestive heart failure (CHF), suggesting that abnormal pulsatile load may contribute to CHF. This study was designed to assess more direct measures of central pulsatile load in CHF. Noninvasive hemodynamic evaluations were performed in 28 subjects with CHF and 40 controls using calibrated tonometry of the brachial, radial, femoral, and carotid arteries along with echocardiographic assessment of left ventricular outflow tract (LVOT) diameter and Doppler flow. Characteristic impedance (Z(c)) was calculated as the ratio of DeltaP (carotid) and DeltaQ (LVOT flow) in early systole. Carotid-radial (CR-PWV) and carotid-femoral (CF-PWV) pulse wave velocities were calculated from tonometry. Augmentation index was assessed from the carotid waveform. Total arterial compliance (TAC) was calculated using the area method. Brachial pulse pressure was elevated (62+/-16 versus 53+/-15 mm Hg, P=0.015) in CHF because of lower diastolic pressure (66+/-10 versus 73+/-9 mm Hg, P=0.003). CHF had higher Z(c) (225+/-76 versus 184+/-66 dyne. sec. cm(-5), P=0.020). CF-PWV did not differ (9.7+/-2.7 versus 9.2+/-2.0, P=0.337), whereas CR-PWV was lower in CHF (8.6+/-1.4 versus 9.4+/-1.5, P=0.038). There was no difference in TAC (1.4+/-0.5 versus 1.4+/-0.6 mL/mmHg, P=0.685), and augmentation index was lower in CHF (8+/-17 versus 21+/-13%, P=0.001). CHF subjects have elevated central pulsatile load (Z(c)), which is not apparent in global measures such as augmentation index or TAC, possibly because of contrasting changes in central and peripheral conduit vessels. This increased pulsatile load represents an important therapeutic target in CHF.

Arteries↗
PubMed2001

Remodeling of atrial dimensions and emptying function in canine models of atrial fibrillation.

OBJECTIVES: Atrial tachycardia-induced remodeling (ATR) and ventricular tachypacing-induced heart failure (HF) create experimental substrates for atrial fibrillation (AF), and both have been reported to produce atrial dilation and hypocontractility. The relative importance of changes in atrial size and contractility in the two models is unknown. This study compared changes in atrial dimensions and emptying in ATR versus HF dog models and related them to AF promotion. METHODS: In ATR dogs (n=11), the right atrium (RA) was paced at 400/min for 42 days. In HF dogs (n=10), the right ventricle was paced at 240 bpm for 2 weeks, followed by 3 weeks at 220 bpm. Transthoracic echocardiography was performed at baseline and weekly thereafter. At a terminal electrophysiological study, RA effective refractory period (ERP) was recorded and AF induced repeatedly by atrial burst pacing to measure mean AF duration (DAF). RESULTS: Left atrial (LA) systolic area increased by 10.0% in ATR versus 48.2% in HF dogs (P=0.008), with significant time-dependent changes in HF (P=0.0001), but not ATR (P=0.16). LA diastolic area increased over time in both groups (P=0.004, 0.0001 for ATR and HF respectively), but increases were much larger in CHF (80.2%) compared to ATR (24.2%, P=0.0002). Similar findings were obtained for RA. Fractional area shortening (FAS) decreased by 19.4% (ATR) versus 41.8% (HF, P=0.007) in LA and 13.7% (ATR) versus 33.7% (HF, P=0.03) in RA. RA ERP correlated with DAF in ATR dogs (r=-0.79, P<0.001), but not in HF dogs (r=0.20, P=NS). DAF and diastolic areas of RA and LA were highly correlated (r=0.71, 0.77; P<0.01 for each) in HF dogs, but not in ATR dogs (r=-0.18, 0.29; P=NS). CONCLUSIONS: Remodeling of atrial size and emptying function is much greater in HF than in ATR. Whereas in ATR, electrophysiological remodeling is of prime importance in AF promotion, structural remodeling (as reflected in changes in atrial size and contraction) appears much more important in HF-induced AF.

Animals↗
PubMed2001

A novel realistic three-layer phantom for intravascular ultrasound imaging.

Intravascular ultrasound (IVUS) is an imaging modality that experienced a tremendous development over the last 20 years. Phantoms for IVUS are rare and poorly documented. The aim of this paper is to propose an original IVUS phantom that has geometries and specular textures closer to those of coronary arteries than conventional tube-like phantoms. The proposed phantom has a three-layer aspect, reproducing the intima, media and adventitia that compose the arterial wall. It is made of an agar-based compound, with water, glycerol and cellulose particles. Fourteen phantoms were quantified using IVUS. Six phantoms were evaluated by both photomacroscopy and IVUS. There was an excellent correlation between phantom dimensions evaluated by photomacroscopy and the nominal values (mold dimensions). The IVUS quantification of the phantom was closely correlated to the measurements obtained by photomacroscopy. These results demonstrate that a multilayer phantom, with known and reproducible dimensions and with realistic geometric and echographic properties has been developed.

Arteries↗
PubMed2001

Atrioventricular interval optimization and exercise tolerance.

Modern pacemakers offer many programming options regarding the AV interval including the ability to vary AV intervals depending on whether atrial activity is paced or spontaneous and to shorten AV intervals with increasing rates. To determine if optimization of these features improves exercise tolerance, 14 patients with intact sinus node function and AV block treated with dual chamber pacemakers were enrolled in a randomized double-blind crossover trial. Doppler echocardiographic measurements of cardiac index and mitral flow were assessed over a range of programmable AV intervals at rest to determine each patient's optimal AV interval. Eleven patients completed serial graded exercise tests with spiroergometry after randomly programming the AV interval three ways in a crossover manner: fixed AV interval = 150 ms without rate adaptation (150/Fixed), fixed AVinterval = 150 ms with rate adaptation (150/R), or optimized AV interval with rate adaptive AV interval shortening (optimized/R). Exercise capacity was determined by maximum oxygen uptake. Ten men and four women, age 64 +/- 8 years, were enrolled. At rest, optimization of the AVintervalimproved the cardiac index by 21% (P < 0.001) and mitral flow by 13.4% (P < 0.001) when compared to least-favorable AV intervals. During exercise, no differences in maximum heart rates were noted. Maximum oxygen uptake was increased in both groups with rate adaptive AVinterval shortening when compared tofixed AVinterval without rate adaptation: 13.9% (adjusted P < 0.04) and 14.6% (adjusted P < 0.02) in optimized/R and 150/R, respectively. No differences were noted between optimized/R and 150/R. In conclusion, rate adaptive AV interval shortening improved exercise tolerance independent of changes in heart rate. However, optimization of the AV interval with Doppler echocardiography at rest did not further improve exercise capacity.

Atrial Function↗
PubMed2001

Catheter cryoablation of the atrioventricular node in patients with atrial fibrillation: a novel technology for ablation of cardiac arrhythmias.

INTRODUCTION: Recent animal studies demonstrated the feasibility and safety of applying percutaneous catheter cryoablation technology for ablation of arrhythmogenic sites. The studies also showed that reversible "ice mapping" can be performed before creating permanent lesions. We investigated the feasibility and safety of applying this new technology in man. METHODS AND RESULTS: Cryoablation of the AV node (AVN) using a 9-French quadripolar catheter with a 4-mm electrode tip was attempted in 12 patients (mean age 67.8 +/- 11.4 years) with refractory atrial fibrillation. Whereas technical issues prevented adequate tissue contact in two patients, complete AVN block was obtained in the remaining 10 patients after 4.8 +/- 1.9 cryoapplications lasting 5.5 +/- 0.2 minutes resulting in temperatures of -58.1 degrees +/- 5.4 degrees C. In all patients with sinus rhythm at the time of the procedure, cryomapping at warmer temperatures induced reversible AVN block and allowed confirmation of a successful site before definitive ablation. Intracardiac echocardiography was performed in three patients and allowed visualization of the cryocatheter-endocardial contact and cryolesion formation. No major procedural complications were reported. After 6 months of follow-up, 8 of 10 initially successful patients remained in complete block; 1 had partial recovery of AVN conduction manifested by atrial fibrillation with a slow ventricular response, and 1 fully recovered AVN conduction. CONCLUSION: (1) Catheter cryoablation of the AVN can be performed safely in man. (2) Reversible cryomapping is feasible and may offer an advantage over radiofrequency ablation. (3) Cryocatheter-endocardial contact and cryolesion growth can be monitored with intracardiac echocardiography.

Aged↗
PubMed2001

Cardiac-directed overexpression of wild-type alpha1B-adrenergic receptor induces dilated cardiomyopathy.

Using transgenesis as a paradigm, we show here that alpha1-adrenergic receptors (alpha1AR) play an important role in cardiac homeostasis. Cardiomyocyte-specific overexpression of the alpha(1B)AR subtype resulted in the development of dilated cardiomyopathy and death at ~9 mo of age with typical signs of heart failure. Histological analyses showed the enlargement of all four cardiac chambers and cardiomyocyte disarray in the failing hearts. Transgenic animals showed increased left ventricular areas, as assessed by echocardiography. In addition, a progressive decrease in left ventricular systolic function was revealed. The abundance and activity of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2) were reduced, and the ratio of phospholamban to SERCA2 was increased. alpha-Myosin heavy chain (MHC) mRNA was less abundant in older transgenic ventricles, whereas beta-MHC was induced in the failing hearts. Titin mRNA abundance was decreased at 9 mo, whereas atrial natriuretic factor mRNA was elevated at all times. This model mimics structural and functional features of idiopathic dilated cardiomyopathy. The results of this study suggest that chronic alpha1AR activity is deleterious for cardiac function.

Animals↗
PubMed2001

Intravascular ultrasound assessment of pulmonary vascular disease in patients with pulmonary hypertension.

BACKGROUND: Measurements of pulmonary pressure and resistance are still considered to be the "gold standard" in the evaluation of pulmonary hypertension (PH), despite their limitations in predicting irreversible disease. Hemodynamic assessment also only provides a global evaluation of the pulmonary vascular bed, whereas PH is an inhomogeneous disease of the vessel wall. METHODS AND RESULTS: We assessed the value of intravascular ultrasound (IVUS) in 30 patients with suspected PH and correlated the structural changes in distal pulmonary arteries found on IVUS with conventional hemodynamic data. Plasma endothelin (ET)-1 levels and pulmonary ET-1 extraction also were measured as markers of the severity of PH. The anatomic abnormalities revealed by IVUS were more severe in the lower lobes than in the upper lobes, as evidenced by the greater percentage of wall thickness (WT), the smaller lumen diameter/WT and lumen area/total vessel area (p < 0.05 for each). IVUS anatomic indexes correlated directly with hemodynamic data (eg, with pulmonary arterial systolic pressure; r = 0.56; p < 0.001) and ET-1 levels but inversely with pulmonary ET-1 extraction. CONCLUSION: Patients with PH have greater pulmonary arterial WT that is more severe in the lower lobes than in the upper lobes. The severity of structural abnormalities found on IVUS is directly correlated with hemodynamic findings and ET-1 levels. IVUS may provide useful additional information in the assessment of patients with PH.

Adult↗
PubMed2001

Impact of residual plaque burden after balloon angioplasty in the MultiVitamins and Probucol (MVP) trial.

BACKGROUND: It has been shown in the MultiVitamins and Probucol (MVP) trial that probucol reduces angiographic lumen loss by 68% after percutaneous transluminal coronary angioplasty (PTCA). Restenosis occurred in 40% of patients not treated with probucol and in 20% of those in the probucol alone group. OBJECTIVE: To determine the morphological predictors of restenosis in patients treated with probucol. PATIENTS AND METHODS: Beginning 30 days before angioplasty, 317 patients were randomly assigned to receive probucol, multivitamins, the combined treatment or placebo. Patients were then treated for six months after angioplasty. Intravascular ultrasound (IVUS) examination was performed immediately after angioplasty and at follow-up in 94 patients (108 segments). The angioplasty operator was blinded to the IVUS results. The cross-section selected for serial analysis was the one at the angioplasty site with the smallest lumen area at follow-up. Receiver operating characteristic curves were used to determine the performance of criteria to predict angiographic restenosis at follow-up. RESULTS: In probucol-treated patients, the cross-sectional area (CSA) narrowing of 67.6% or less was the best IVUS predictor for the absence of restenosis (P=0.03). Diameter stenosis of 35% or less almost reached significance as a predictor in these patients (P=0.056). The restenosis rate when either of these predictors was met was less than 13%. Rates of repeat PTCA in patients treated with probucol were 9.7% when CSA narrowing was 67.6% or less on IVUS and 3.1% with a post-PTCA stenosis of 35% or less on quantitative coronary angiography (QCA). No predictor of the absence of restenosis in patients not treated with probucol was identified. CONCLUSIONS: The presence after balloon angioplasty of a CSA narrowing of 67.6% or less on IVUS or a diameter stenosis of 35% or less on QCA is associated, in patients treated with probucol, with extremely low rates of coronary restenosis and repeat angioplasty.

Angioplasty, Balloon, Coronary↗
PubMed2000

Randomized trial comparing intravenous nitroglycerin and heparin for treatment of unstable angina secondary to restenosis after coronary artery angioplasty.

BACKGROUND: The treatment of unstable angina targets the specific pathophysiological thrombotic process at the site of the active culprit lesion. In unstable angina due to a restenotic lesion, smooth muscle cell proliferation and increased vasoreactivity may play a more important role than thrombus formation. Therefore, the relative benefits of nitroglycerin and heparin might differ in unstable angina associated with restenosis compared with classic unstable angina. METHODS AND RESULTS: We randomized 200 patients hospitalized for unstable angina within 6 months after angioplasty (excluding those with intracoronary stents) to double-blind administration of intravenous nitroglycerin, heparin, their combination, or placebo for 63+/-30 hours. Recurrent angina occurred in 75% of patients in the placebo and heparin-alone groups, compared with 42.6% of patients in the nitroglycerin-alone group and 41.7% of patients in the nitroglycerin-plus-heparin group (P<0.003). Refractory angina requiring angiography occurred in 22.9%, 29.2%, 4. 3%, and 4.2% of patients, respectively (P<0.002). The odds ratios for being event free were 0.24 (95% CI, -0.13 to 0.45, P=0.0001) for nitroglycerin versus no nitroglycerin and 0.98 (95% CI, -0.55 to 1. 73, P=NS) for heparin versus no heparin. No patient died or suffered myocardial infarction. CONCLUSIONS: Intravenous nitroglycerin is highly effective in preventing adverse ischemic events (recurrent or refractory angina) in patients with unstable angina secondary to restenosis, whereas heparin has no effect.

Aged↗
PubMed2000

The effects of intracoronary brachytherapy on the natural history of postangioplasty dissections.

OBJECTIVES: The aim of this study was to determine the natural history of postangioplasty intravascular ultrasound (IVUS)-detected dissections and to assess the influence of intracoronary beta-radiation on dissection resolution. BACKGROUND: Intracoronary radiotherapy is considered to impair exaggerated vessel healing. Conversely, excessive healing impairment may increase the risk of complications due to unhealed dissection. Alternatively, residual dissection may represent an innocent marker of adequate therapy. METHODS: Immediate postangioplasty and six-month follow-up IVUS studies of 94 patients in the IVUS substudy of the MultiVitamins and Probucol (MVP) trial and 26 nonstented patients in the Beta Energy Restenosis Trial (BERT) were analyzed for the presence or absence of dissection. RESULTS: Of the 28 patients with postangioplasty dissections in MVP, only one had evidence of residual dissection at six months (95% confidence interval [CI] for failure rate 0.2%; 20.2%). Conversely, 9 of 16 dissections had healed in BERT (95% CI for failure rate 30.6%; 79.2%) (p < 0.0002). Nevertheless, an index based on dissection arc and length demonstrated improvement in the irradiated patients. Irradiated patients with residual dissections showed significant increase in lumen area at six-months (5.10 +/- 0.98 to 7.11 +/- 2.61 mm2, p < 0.02) not noted when there was resolution of the dissection (6.03 +/- 2.38 to 6.36 +/- 3.33 mm2, p = NS). In both groups the external elastic membrane area was unchanged at follow-up. CONCLUSIONS: Resolution appears to be the natural history of IVUS-detected dissections in most cases. Significant resolution of dissection occurs following intracoronary beta-radiation as reflected in reduced dissection index at six-months in these patients, although significant impairment of vessel wall healing was noted.

Aortic Dissection↗
PubMed2000

Reliability of mechanical and phased-array designs for serial intravascular ultrasound examinations--animal and clinical studies in stented and non-stented coronary arteries.

BACKGROUND: Both mechanical and multi-element intravascular ultrasound designs have potential advantages and limitations that may impact on their value for clinical and research purposes. Determination of the reproducibility of measurements is critical before a given system can be used in studies such as regression of atherosclerosis trials. METHODS: We performed serial intravascular ultrasound imaging with catheters using mechanical and phased-array designs in stented and non-stented coronary arteries in dogs and in patients. RESULTS: Both systems correlated well for areas (r > or = 0.90, p < 0.0001) and diameters (r > or = 0.84. p < 0.0001) in dogs and in patients. There was a slight difference between multi-element and mechanical designs for measurements of area (mean difference in dogs and in patients: -0.24 and 0.96 mm2, p < 0.055) and diameter (-0.08 and 0.16 mm, p < 0.0001). The reproducibility of the multi-element system for reanalysis of the same frames and for analysis of serial pullbacks was similar to the same measurements with the mechanical system (r > or = 0.96 for all measurements). The differences in absolute and relative variability between the mechanical and phased-array designs, both for reanalysis of same frames and serial pullbacks, were very small. CONCLUSIONS: Although multi-element and mechanical intravascular ultrasound designs are not strictly interchangeable, their similar reproducibility and the small differences in measurements demonstrate that both designs are acceptable alternatives for trials of regression of atherosclerosis. Determination of the variability for serial pullbacks of both designs was also important to assess the statistical power of such trials.

Animals↗
PubMed2000

Obstruction of left ventricular outflow tract by vegetation and periaortic abscess.

Echocardiography is the modality of choice for the noninvasive recognition of vegetations and abscesses that complicate endocarditis. Vegetation size is highly variable, and it has been suggested that large vegetations are related to a more complicated course. The case we present is unusual in that the echocardiographically detected vegetation was very large, highly mobile, and caused severe obstruction of the left ventricular outflow tract, which led to impaction and cardiac arrest.

Adult↗
PubMed2000

Prolonged distress and clinical deterioration before pericardial drainage in patients with cardiac tamponade.

OBJECTIVE: To determine whether patients with cardiac tamponade are subject to delays and clinical deterioration before undergoing echocardiography and pericardial drainage. DESIGN: Retrospective study. SETTING: The Montreal Heart Institute, Montreal, Quebec, a cardiology referral centre. PATIENTS: The charts of 50 patients who presented with tamponade were reviewed. Intervals between the appearance of symptoms, consultation, echocardiography and drainage were noted. The presence of clinical deterioration before drainage was evaluated. Causes for delays were investigated. RESULTS: Previous cardiac surgery (74%) was the most common etiology of tamponade. Symptoms were present 6.6+/-5.8 days before consultation. The delay between consultation and echocardiography was 1.2+/-2.0 days (range 0 to 12), and that between echocardiography and drainage was 0.8+/-0.9 days (range 0 to four). Patients underwent drainage 1. 9+/-2.5 days (range 0 to 16) after the initial consultation. Deterioration of the clinical status was noted in 34% of patients before pericardial drainage. An error in the initial diagnosis was present in 36% of patients; the majority of these were incorrectly diagnosed with heart failure. Another 44% of patients had no mention of either a working diagnosis in the chart at admission or the desire to rule out tamponade on the request for echocardiography. CONCLUSION: The proper diagnosis does not appear to be initially considered in up to 80% of patients who present with cardiac tamponade. Clinical deterioration occurs in approximately a third of patients during the interval between consultation and pericardial drainage.

Adult↗
PubMed2000

Insights into oxidative stress and atherosclerosis.

Compelling evidence points to oxidative stress as an important trigger in the complex chain of events leading to atherosclerosis. Randomized clinical trials have not provided definitive evidence of the beneficial effect of antioxidant vitamins. Problems associated with the use of vitamins include their potential pro-oxidant effects and the decreased absorption of natural gamma-tocopherol caused by alpha-tocopherol supplements. Probucol and amlodipine are more powerful lipophilic antioxidants than vitamin E. They also do not appear to have significant pro-oxidant properties. Probucol has been shown to prevent coronary restenosis after balloon angioplasty in clinical trials. Its high density lipoprotein-lowering effect, however, prevents it from being protective against progression of coronary atherosclerosis. Slowing or reversing the atherosclerotic process with an antioxidant likely requires the use of a powerful lipophilic antioxidant that has neutral or positive effects on serum lipids when given alone or in combination with a lipid-lowering agent.

Angioplasty, Balloon, Coronary↗