Role of tachycardia as an inotropic stimulus in man.

We examined the inotropic effect of tachycardia in nine postsurgical aortocoronary bypass graft patients (with intact cardiac innervation) and nine cardiac allograft recipients (with denervated hearts). The changes in stroke volume (SV) and velocity of circumferential fiber shortening (VCF) which accompany sudden increases and decreases in atrial pacing frequency were determined by computer-aided fluoroscopic analysis of the motion of surgically implanted midwall myocardial markers. Because the first beat after a change in rate retains the frequency characteristics of the preceding rate, we compared the first posttachycardia beat with control beats and late tachycardia beats with the first tachycardia beat; afterload and preload for each pair of beats were similar. For an increase in heart rate of 50 beats/min, SV and VCF rose 79 and 64% from the first tachycardia beat to late tachycardia beats, and SV and VCF rose 8 and 35% from control beats to the first posttachycardia beat in the innervated group. Responses in the denervated group were not significantly different from those in the innervated group. The degree of the inotropic response was positively correlated with the magnitude of the increase in heart rate (r = 0.91). The decay in augmented contractility after decreasing the rate back to control levels fits an exponential relationship with a mean t((1/2)) of 1.7 s. Thus, in conscious man, increases in heart rate represent a positive inotropic stimulus, independent of other factors influencing ventricular performance and unaffected by neural innervation, and should be considered when changes in cardiac function are interpreted during serial studies or after drug administration.

1996 AUR Memorial Award. Densitometric analysis of eccentric vascular stenoses: comparison of CO2 and iodinated contrast media.

RATIONALE AND OBJECTIVES: The authors compared the accuracies of CO2 and iodinated contrast material in the densitometric quantification of eccentric vascular stenoses. METHODS: Five precision-machined eccentric phantom stenoses of 50%, 60%, 70%, 80%, and 90% cross-sectional area narrowing were integrated into a pulsatile ex vivo flow model, imaged with digital subtraction angiography (DSA), and analyzed with densitometry. Relationships between the actual and measured (densitometric) degree of cross-sectional area narrowing were evaluated by using linear regression analysis and paired Student t tests. Comparison measurements were obtained in en face and profile projections. In addition, the effect of iodinated contrast material concentration was evaluated over a range of dilutions (47-282 mg iodine per milliliter). RESULTS: CO2 yielded significantly more accurate results than did iodinated contrast material (282 mg iodine per milliliter) in the 50%, 60%, and 70% stenosis models when imaging was performed en face (P < .005). The best overall correlation was observed with CO2 DSA when imaging in profile (slope = 0.91, intercept = 2.42% actual stenosis, r = .99). The accuracy of densitometric stenosis estimation was inversely related to the concentration of iodinated contrast material. CONCLUSION: CO2 DSA densitometry, under the conditions of these experiments, yields quantitative measures of relative cross-sectional area narrowing that are comparable with, and under some circumstances surpass, those obtained with iodinated contrast material-based DSA. In this model, CO2 was more useful than iodinated contrast material in 50%-70% stenosis when imaging in the least-optimal plane of stenosis quantification, the en face projection.

Communication between the two pleural cavities after major cardiothoracic surgery: relevance to percutaneous intervention.

The authors describe evidence of communication between the two pleural cavities after major cardiothoracic surgery (combined heart and lung transplantation, heart transplantation, and correction of complex congenital heart disease) performed in three patients. In two patients, unilateral lung biopsy caused a symptomatic bilateral pneumothorax. This was successfully treated with insertion of a single chest tube in one patient and two chest tubes in the other patient. In the third patient, simultaneous evacuation of large bilateral pleural effusions was performed by means of unilateral thoracentesis because of the presence of a common pleural cavity.