Intraaortic balloon counterpulsation enhances coronary thrombolysis induced by intravenous administration of a thrombolytic agent

OBJECTIVES

This study was designed to test the hypothesis that in the presence of moderate hypotension, intraaortic balloon counterpulsation would enhance coronary thrombolysis induced by intravenous administration of recombinant tissue-type plasminogen activator (rt-PA).

BACKGROUND

Although many studies have confirmed the efficacy of thrombolytic therapy in acute myocardial infarction, few have systematically investigated the effects of alterations in aortic pressure on coronary thrombolysis, and none have previously investigated the effects of intraaortic balloon counterpulsation on thrombolysis.

METHODS

The effects of intraaortic balloon counterpulsation on aortic pressure, coronary blood flow and coronary thrombolysis were studied in a canine model. Coronary thrombosis was induced in eight dogs by injection of radioactive blood clot through a catheter placed in the left anterior descending coronary artery. Subsequently, dogs underwent phlebotomy to decrease systolic aortic pressure to approximately 90 mm Hg. After phlebotomy, during a 15-min interval of intravenous administration of rt-PA, coronary thrombolysis and coronary flow were determined during and in the absence of counterpulsation.

RESULTS

Intraaortic balloon counterpulsation significantly increased aortic diastolic pressure. Corresponding to the increase in pressure, intraaortic balloon counterpulsation significantly increased the rate of rt-PA-induced coronary thrombolysis. Although not statistically significant, peak diastolic coronary flow tended to increase with counterpulsation.

CONCLUSIONS

These results indicate that in the presence of moderate systemic hypotension, intraaortic balloon counterpulsation enhances the rate of rt-PA-induced coronary thrombolysis.

p53 gene mutations in Chinese human testicular seminoma

Genomic deoxyribonucleic acid from 17 primary human testicular seminomas was screened for the presence of mutations in exons 5 to 8 of gene p53, using the single strand conformation polymorphism assay, followed by direct deoxyribonucleic acid sequencing. The p53 mutations in 1 allele leading to an amino acid change but a normal (wild-type) sequence in the remaining allele were identified in 4 of 17 seminomas (23.5%). Sites of mutations were in exon 5 (codon 141), exon 7 (codon 238, codon 258) and exon 8 (codon 270). The present study suggested that mutation of the p53 gene is involved in the development of human testicular seminoma as in the case of several other types of human cancers.

Mesonephric contribution to testis differentiation in the fetal mouse

Testes from 11.5-day-old mouse embryos, with and without attached mesonephroi, were cultured for 7 days. Isolated testes failed to develop well-differentiated testis cords: however, when cultured attached to a mesonephros from either a male or a female donor embryo, testes developed cords that were normal in appearance. Testes cultured next to a mesonephric region but separated from it by a permeable filter, did not develop normal cords, nor did testes grafted to fragments of embryonic limb or heart. When testes were grafted to mesonephric regions from mice carrying a transgenic marker, the marker was found in some of the peritubular myoid cells and other interstitial cells of the testis, but not in the Sertoli cells or the germ cells. We conclude that after 11.5 days post coitum, cells can migrate from the mesonephric region into the differentiating testis and can contribute to the interstitial cell population, and that this contribution is necessary for the establishment of normal cord structure. The germ cells in all cultured testes, whether or not differentiated cords were present, were T1 prospermatogonia: no meiotic germ cells were seen.

Digital subtraction angiography in the diagnosis of congenital heart diseases: analysis of 60 cases

Ninety-one IVDSA and/or IADSA examinations with 192 injections were performed in 60 patients with congenital heart disease (CHD), including 31 anatomic anomalies. Axial projection was used in 23 patients. Analysis of the results of this series showed that accurate diagnosis by DSA confirmed by cardiac surgery together with definite diagnosis by DSA were obtained in 54 cases (90%). Two cases of nondiagnosis by DSA resulted from a suboptimal DSA method; four cases of partially accurate or mistaken diagnosis determined by cardiac surgery occurred because the axial view was not used and/or the anomalies were too small to be visualized by DSA. To increase the diagnostic accuracy of DSA in CHD, an optimal method of DSA must be selected according to the position of the anomaly and the hemodynamic data, and the axial view should be used to visualize the anomaly clearly in complex cases. In addition, DSA may fail to define a mild anomaly because of its lower spatial resolution.

Marked systemic hypotension depresses coronary thrombolysis induced by intracoronary administration of recombinant tissue-type plasminogen activator

OBJECTIVES

This study was designed to test the hypothesis that the level of aortic blood pressure affects the rate and extent of coronary thrombolysis induced by intracoronary administration of recombinant tissue-type plasminogen activator (rt-PA).

BACKGROUND

Although many studies have confirmed the efficacy of thrombolytic therapy in the treatment of acute myocardial infarction, the effects of altered blood pressure on coronary thrombolysis have not been studied. Because the aortic pressure represents the coronary artery inflow pressure, first principles predict that changes in blood pressure will affect the delivery of the thrombolytic agent and thus affect thrombolysis.

METHODS

The effects of large changes in blood pressure on coronary thrombolysis were studied in a canine model. Coronary thrombosis was induced by injection of radioactive blood clot through a catheter placed in the left anterior descending coronary artery. Subsequently, 24 dogs were classified into three groups of 8 dogs each: Group 1 dogs underwent phlebotomy to adjust systolic blood pressure to 130 mm Hg; Group 2 dogs underwent phlebotomy to decrease systolic blood pressure to 75 mm Hg. Dogs in Group 3 also underwent phlebotomy to achieve a systolic blood pressure of 75 mm Hg and then received norepinephrine to increase this pressure to 130 mm Hg. After adjustment in blood pressure, all dogs received an infusion of rt-PA (0.25 mg/kg body weight) over 30 min through the left anterior descending artery catheter. In a fourth group of six dogs, the effect of altered blood pressure on the rate of coronary thrombolysis was assessed.

RESULTS

In dogs in Groups 1 and 3, the rate and extent of coronary thrombolysis were significantly increased compared with values in Group 2. In each of the six Group 4 dogs the rate of coronary thrombolysis increased when norepinephrine increased systolic blood pressure from 75 to 130 mm Hg.

CONCLUSIONS

These results indicate that a moderate increase in coronary inflow pressure increases the rate and extent of coronary thrombolysis compared with values during marked systemic hypotension.

Social support among the aged in Wuhan, China

"This study provides information on supportive social relations in a sample of 2,762 elderly people in Wuhan, China. The elderly concerned were found to be actively engaged in exchanges of social support with their families and kin. They not only receive assistance but also provide a substantial amount of help to others. These supportive ties were highly positive and satisfactory to the great majority of the respondents. Only moderate correlations were found among various dimensions of social support. These results underscore the multi-dimensional nature of social support and suggest that caution needs to be exercised in extrapolating interpersonal exchanges from social embeddedness."

Pulmonary vascular pressure-flow characteristics. Effects of dopamine before and after pulmonary embolism

We compared the general hemodynamic effects of dopamine and dobutamine in dogs with acute pulmonary hypertension complicated by a decrease in cardiac output (CO). The pulmonary hypertension was induced by injection of autologous blood clot. Emboli markedly increased mean pulmonary artery pressure (Ppa) and decreased CO (both p < 0.001). Both dopamine and dobutamine increased CO 50% (p < 0.05) and decreased pulmonary vascular resistance (PVR) (p < 0.05), calculated as (PAP - left ventricular end diastolic pressure)/CO. Mean PVR (mm Hg/L/min) decreased from 16.1 to 12.4 with dopamine and from 16. to 11.9 with dobutamine, both p < 0.05. Ventricular filling pressures were not affected. In another 12 dogs we investigated the effects of both drugs on pulmonary pressure-flow (P-Q) characteristics. P-Q characteristics were determined in dogs with normal Ppa values and in those with embolic pulmonary hypertension. The slope of the P-Q relationship defines the incremental vascular resistance and the extrapolated pressure intercept, the effective vascular outflow pressure. All P-Q relationships were described well by a linear equation. Despite significant systemic effects in both groups and despite a decrease in PVR with both drugs in embolized dogs, neither drug significantly affected pulmonary P-Q characteristics. The discrepancy between PVR and incremental resistance is explained by an incorrect assumption in PVR that the left ventricular filling pressure is the effective vascular outflow pressure. We conclude that both before and after the induction of pulmonary hypertension, both dopamine and dobutamine improve CO without affecting pulmonary vascular tone.

Coronary thrombolysis. Comparative effects of intracoronary administration of recombinant tissue plasminogen activator and urokinase

We employed a canine model of coronary thrombosis, induced by injection of radioactive blood clot, via a catheter placed in the left anterior descending coronary artery, to compare effects of intracoronary administration of recombinant tissue plasminogen activator (rtPA) and urokinase (UK) on rate and extent of coronary thrombolysis. Two doses of UK, 15,000 U/kg (UK15) and 30,000 U/kg (UK30) and two doses of rtPA, 0.25 mg/kg (rtPA.25) and 0.75 mg/kg (rtPA.75) were given. Drugs were infused over 45 min. Compared with the other regimens, rate and extent of coronary thrombolysis were significantly increased with rtPA.75. Also, despite a much higher dose of UK, coronary thrombolysis was similar with UK30 and rtPA.25. Compared with UK15, rate and extent of coronary thrombolysis were increased with rtPA.25. These results indicate that intracoronary administration of rtPA is superior to intracoronary UK in inducing thrombolysis.

Effect of low-molecular-weight heparin on recombinant tissue plasminogen activator-induced thrombolysis in canine pulmonary embolism

We employed a canine model of pulmonary embolism induced by radioactive blood clots to determine if low-molecular-weight heparin augments recombinant tissue plasminogen activator (rtPA)-induced thrombolysis. Following embolization, dogs were randomized: group 1 dogs received heparin; group 2 dogs received low-molecular-weight heparin; group 3 dogs received 1.5 mg/kg of rtPA over 45 minutes; group 4 dogs received rtPA 3 mg/kg over 45 minutes; and group 5 dogs received 1.5 mg/kg of rtPA plus low-molecular-weight heparin. Over three hours, little thrombolysis occurred in groups 1 and 2. In contrast, significant thrombolysis occurred in groups 3 to 5, 46 percent, 49 percent, and 46 percent, respectively (all p less than 0.01 compared with groups 1 and 2). We conclude that there is an upper limit to the dose-thrombolytic rate relationship with rtPA, and that low-molecular-weight heparin does not augment rtPA-induced thrombolysis.

Digital angiographic impulse response analysis of regional myocardial perfusion. Estimation of coronary flow, flow reserve, and distribution volume by compartmental transit time measurement in a canine model

A system impulse response function that describes the kinetics of radiographic contrast material transit through the coronary circulation was calculated from 175 selective digital angiograms of normal and stenotic arteries in 10 dogs during rest and hyperemia. The goal of the study was to determine if the flow and distribution volume characteristics of the epicardial coronary arteries and the myocardial microcirculation could be stimulated by specific mathematical compartments of a lagged normal density model impulse response function in which the flow/distribution volume ratio is the inverse of the mean transit time. The arterial compartment mean transit time correlated with flow (r = 0.75); however, the correlation was significantly improved in individual dogs (r = 0.83 +/- 0.13; p less than 0.005) and was highly dependent on the length of the conduit vessel. The microcirculation compartment mean transit time was distributed as two populations with respect to flow. There was a linear correlation during hyperemia (r = 0.87) and a nonlinear relation during rest, which was characteristic of an autoregulating system. Resting values of microcirculation compartment mean transit time correlated with coronary flow reserve (r = 0.84) and differed significantly between vessels that were normal and those with subcritical stenosis, critical stenosis, or total occlusion (p less than 0.01 for all comparisons). The estimated microcirculation compartment distribution volume increased from a minimum of 4.0 +/- 1.5 ml/100 g myocardium in normal vessels with resting flow to 11.2 +/- 3.5 ml/100 g during hyperemia. These data suggest that the model compartments functionally describe the physiological behavior of their anatomic analogues and permit the quantification of microcirculatory autoregulation from a single measurement at rest without provoking hyperemia.