[Photon radiation-induced structural and functional changes in the myocardium of hypertensive SHR rats]

Male rats were irradiated by a Korobkov photon light-emitting diode matrix with a maximum irradiation at 612 nm every day 1 h per day for 13 days. After a course of irradiation, the rhythmoinotropic characteristics of the cardiac muscle significantly improved. Exposure to photon radiation initiated an active rearrangement in myocytes as shown by a morphological analysis. Considerable changes were found in the structure of sarcoplasmic reticulum (SR); the area of SR profiles increased more than twofold compared to control. This suggests a proportional increase in the ability of SR to absorb calcium, due to both an increase in its buffer capacity and possibly, an improved functioning of Ca2+ ATPase of the reticulum. Probably, the photon therapy leads to the normalization of calcium homeostasis in myocytes and improvement of the characteristics of the cardiac muscle contraction-relaxation cycle. Furthermore, changes in the proportions of the myocardium capillaries (increased by 75% compared to control; p < 0.001) and the area of mitochondrial profiles of myocytes (increased by 13%; p < 0.05) were observed, which lead to more active metabolic processes and a rise in energy potential in myocardial cells after photon radiation treatment.

The effect of continuous light exposure of rats on cardiac response to ischemia-reperfusion and NO-synthase activity

Factors modulating cardiac susceptibility to ischemia-reperfusion (I/R) are permanently attracting the attention of experimental cardiology research. We investigated, whether continuous 24 h/day light exposure of rats can modify cardiac response to I/R, NO-synthase (NOS) activity and the level of oxidative load represented by conjugated dienes (CD) concentration. Two groups of male adult Wistar rats were studied: controls exposed to normal light/dark cycle (12 h/day light, 12 h/day dark) and rats exposed to continuous light for 4 weeks. Perfused isolated hearts (Langendorff technique) were exposed to 25 min global ischemia and subsequent 30 min reperfusion. The recovery of functional parameters (coronary flow, left ventricular developed pressure, contractility and relaxation index) during reperfusion as well as the incidence, severity and duration of arrhythmias during first 10 min of reperfusion were determined. The hearts from rats exposed to continuous light showed more rapid recovery of functional parameters but higher incidence, duration and severity of reperfusion arrhythmias compared to controls. In the left ventricle, the NOS activity was attenuated, but the CD concentration was not significantly changed. We conclude that the exposure of rats to continuous light modified cardiac response to I/R. This effect could be at least partially mediated by attenuated NO production.

The incidence and functional consequences of RT-associated cardiac perfusion defects

PURPOSE

Radiation therapy (RT) for left-sided breast cancer has been associated with cardiac dysfunction. We herein assess the temporal nature and volume dependence of RT-induced left ventricular perfusion defects and whether these perfusion defects are related to changes in cardiac wall motion or alterations in ejection fraction.

METHODS

From 1998 to 2001, 114 patients were enrolled onto an IRB-approved prospective clinical study to assess changes in regional and global cardiac function after RT for left-sided breast cancer. Patients were imaged 30 to 60 minutes after injection of technetium 99m sestamibi or tetrofosmin. Post-RT perfusion scans were compared with the pre-RT studies to assess for RT-induced perfusion defects as well as functional changes in wall motion and ejection fraction. Two-tailed Fisher's exact test and the Cochran-Armitage test for linear trends were used for statistical analysis.

RESULTS

The incidence of new perfusion defects 6, 12, 18, and 24 months after RT was 27%, 29%, 38%, and 42%, respectively. New defects occurred in approximately 10% to 20% and 50% to 60% of patients with less than 5%, and greater than 5%, of their left ventricle included within the RT fields, respectively (p = 0.33 to 0.00008). The rates of wall motion abnormalities in patients with and without perfusion defects were 12% to 40% versus 0% to 9%, respectively; p values were 0.007 to 0.16, depending on the post-RT interval.

CONCLUSIONS

Radiation therapy causes volume-dependent perfusion defects in approximately 40% of patients within 2 years of RT. These perfusion defects are associated with corresponding wall-motion abnormalities. Additional study is necessary to better define the long-term functional consequences of RT-induced perfusion defects.

Evaluation of myocardial perfusion and left ventricular function six months after percutaneous transmyocardial laser revascularization: Comparison of two Ho-YAG laser systems with the same wavelength, but different energy delivery and navigation systems

BACKGROUND AND OBJECTIVES

Myocardial perfusion and left ventricular function (LVF) were assessed after percutaneous transmyocardial laser revascularization (PTMR) in patients not amenable to conventional revascularization, with a comparison of two laser systems.

STUDY DESIGN/MATERIALS AND METHODS

PTMR was performed with an Eclipse laser in 15 patients, and with a Biosense DMR in 10 patients. (201)Thallium scintigraphy, coronary angiography, and ventriculography were performed at baseline and at the 7.5+/-4.3-month follow-up. All patients in the Biosense DMR group and 10 in the Eclipse group underwent NOGA mapping before PTMR and after follow-up.

RESULTS

The event-free survival rates were comparable, and the angina scores of all patients improved significantly, but more so in the Biosense DMR group than in the Eclipse group (1.2+/-1.1 vs. 2.3+/-0.9, P < 0.05). Both, the electrical activity assessed by NOGA mapping and the normalized (201)thallium uptake at redistribution improved significantly in the treated segments after Biosense DMR, while the global LVF decreased insignificantly in the Eclipse group.

CONCLUSIONS

PTMR resulted in significant improvements in the clinical symptoms, but the electrical activity improved only in the Biosense DMR group, without transforming to a better LVF.

[Effect of the He-Ne laser irradiation on resistance of the isolated heart to the ischemic and reperfusion injury]

The aim of this work was to investigate the myocardial protection against ischemia/reperfusion using low level laser irradiation (LLLI). It has been shown that pulse pressure was higher in the period of post-ischemic reperfusion as compared with the control group. It provided a better restoration of myocardial contractility as well as increasing of coronary flow in the reperfusion period. The amount of ventricular rhythm disorder episodes decreased. These effects of laser application were registered in conditions of coronary flow reduction less than 50%. One of the suggested mechanisms of laser effect is an ATP-sensitive channel activation.

Symptomatic cardiac events following radiation therapy for left-sided breast cancer: possible association with radiation therapy-induced changes in regional perfusion

Our group has demonstrated that tangential radiation therapy (RT) to the left breast or chest wall can cause perfusion changes in the anterior myocardium. We assess if RT-induced perfusion changes are associated with the development of symptoms consistent with cardiac dysfunction. Between 1998 and 2001, 114 patients were enrolled into an institutional review board-approved prospective study and had pre-RT and serial post-RT (range, 6-24 months) single photon emission computed tomography (SPECT) scans to assess changes in regional cardiac perfusion. Thirty-one patients were excluded. The incidence of cardiac symptoms in patients with and without RT-induced perfusion defects was compared using a 2-tailed Fisher's exact test. With a median follow-up of 16 months (range, 6-24 months), 10 of 83 evaluable patients had > or = 1 episode of transient chest pain, occurring 0-14 months after RT (median, 6 months). The rates of chest pain in the patients with and without new perfusion defects were 9 of 31 and 1 of 52, respectively (P = 0.0004). A similar result was found when patients were segregated based on the use of chemotherapy. Two of these 10 cases were diagnosed as pericarditis. No patient had myocardial infarction or congestive heart failure. Cardiac symptoms occur more frequently in patients with perfusion abnormalities by SPECT after RT than in patients with normal SPECT scans, suggesting that such perfusion defects may be clinically significant. One confounding factor is that women who know they have RT-induced perfusion defects may be more likely to report episode of chest pain. Long-term follow-up will be necessary to better assess the clinical significance of RT-induced perfusion defects.

Effects of amifostine on radiation-induced cardiac damage

The purpose of this study was to investigate whether administration of amifostine prior to irradiation could reduce radiation damage of the rat heart. Female Spraque-Dawley rats were randomized to receive single-dose irradiation (0-22.5 Gy) locally to the heart. Fifteen to twenty minutes before radiation exposure, the animals received either intraperitoneally administered amifostine (160 mg/kg) or buffered saline solution. At 6 months post-irradiation, cardiac function was assessed by the in vitro working rat heart preparation. The severity of interstitial and/or perivascular fibrosis in different anatomical regions of the rat heart was assessed using a semi-quantitative scoring system. Radiation exposure to doses > or = 20 Gy markedly reduced coronary flow, aortic flow and cardiac output. Administration of amifostine prior to radiotherapy afforded protection against these effects and normal cardiac output was maintained, even after 22.5 Gy. A small, non-significant, reduction in histological damage (i.e. perivascular fibrosis and interstitial fibrosis) was also apparent in animals treated with amifostine. There was a clear protective effect of amifostine on the severity and extent of macroscopic damage in lung tissue included in the cardiac irradiation field. The findings of this study suggest that a single dose of amifostine administered prior to irradiation is effective in reducing cardiac damage.

Myocardial perfusion changes in patients irradiated for left-sided breast cancer and correlation with coronary artery distribution

PURPOSE

To evaluate postradiation regional heart perfusion changes with single photon emission tomography (SPECT) myocardial perfusion imaging in 69 patients treated with tangential photon beams radiation therapy (RT) for left-sided breast cancer. To correlate SPECT changes with percent irradiated left ventricle (LV) volume and risk factors for coronary artery disease (CAD).

METHODS AND MATERIALS

Rest SPECT of the LV was acquired pre-RT and at 6-month intervals post-RT. The extent of defects (%) with a severity > 1.5 standard deviations below the mean was quantitatively analyzed for the distributions of the left anterior descending (LAD) artery, left circumflex (LCX) artery, and right coronary artery (RCA) based on computer assisted polar map reconstruction (i.e., bull's-eye-view). Changes in perfusion were correlated with percent irradiated LV receiving > 25 Gy (range 0-32%). Data on patient- and treatment-related factors were collected prospectively (e.g., cardiac premorbidity, risk factors for CAD, chemotherapy, and hormonal treatment).

RESULTS

In the LAD distribution, there were increased perfusion defects at 6 months (median 11%; interquartile range 2-23) compared with baseline (median 5%; interquartile range 1-14) (p < 0.001). There were no increases in perfusion defects in the LCX or RCA distributions. In multivariate analysis, the SPECT perfusion changes in the LAD distribution at 6 months were independently associated with percent irradiated LV (p < 0.001), hormonal therapy (p = 0.005), and pre-RT hypercholesterolemia (p = 0.006). The SPECT defects in the LAD distribution at 12 and 18 months were not statistically different from those at 6 months. The perfusion defects in the LAD distribution were limited essentially to the regions of irradiated myocardium.

CONCLUSION

Tangential photon beam RT in patients with left-sided breast cancer was associated with short-term SPECT defects in the vascular distribution corresponding to the radiation portals. Factors related to the extent of perfusion defects included the percent irradiated LV, hormonal treatment, and pre-RT hypercholesterolemia.

Effect of in vivo heart irradiation on coronary reactivity in the rat

The frequent exposure of the heart to radiation during thoracic tumor radiotherapy often results in chronic impairment of myocardial function. The aim of the present investigation was to evaluate the effect of irradiation on coronary vascular tone in rat hearts exposed in vivo to a single dose of 20 Gy gamma rays. The ability of rat hearts to respond to changes in coronary reactivity was analyzed 1, 15, 30 and 60 days following cardiac irradiation, using the Langendorff model, after perfusion of either L-nitro-arginine (LNA), an inhibitor of nitric oxide synthetase or SIN 1, a nitric oxide donor drug. LNA-induced vasoconstriction and SIN 1-induced vasodilation were lost respectively 15 days and 30 days after irradiation, and associated with smooth muscle cell alterations observed in microscopy, but without any changes in myocardial MDA levels. Thus, our results suggest that 1) endothelium may represent an early and specific radiation target, characterized by radiation-induced vascular tone dysfunctions, with no detectable microscopical changes; 2) alterations are progressive, resulting first from endothelial damage, followed by smooth muscle cell injuries. In conclusion, a local cardiac irradiation induced cellular dysfunction, characterized by a loss of coronary reactivity without changes of the lipid peroxidation index in the hearts.

Cardiac perfusion changes in patients treated for breast cancer with radiation therapy and doxorubicin: preliminary results

PURPOSE

To determine the incidence and dose dependence of regional cardiac perfusion abnormalities in patients with left-sided breast cancer treated with radiation therapy (RT) with and without doxorubicin (Dox).

METHODS

Twenty patients with left-sided breast cancer underwent cardiac perfusion imaging using single photon emission computed tomography (SPECT) prechemotherapy, pre-RT, and 6 months post-RT. SPECT perfusion images were registered onto 3-dimensional (3D) RT dose distributions. The volume of heart in the RT field was quantified, and the regional RT dose was calculated. A decrease in regional cardiac perfusion was assessed subjectively by visual inspection and objectively using image fusion software. Ten patients received Dox-based chemotherapy (total dose 120-300 mg/m(2)), and 10 patients had no chemotherapy. RT was delivered by tangent beams in all patients to a total dose of 46-50 Gy.

RESULTS

Overall, 60% of the patients had new visible perfusion defects 6 months post-RT. A dose-dependent perfusion defect was seen at 6 months with minimal defect appreciated at 0-10 Gy, and a 20% decrease in regional perfusion at 41-50 Gy. One of 20 patients had a decrease in left ventricle ejection fraction (LVEF) of greater than 10% at 6 months; 2/20 patients had developed transient pericarditis. No instances of myocardial infarction or congestive heart failure (CHF) have occurred.

CONCLUSIONS

RT causes cardiac perfusion defects 6 months post-RT in most patients. Long-term follow-up is needed to assess whether these perfusion changes are transient or permanent and to determine if these findings are associated with changes in overall cardiac function and clinical outcome.

Thallium-201 scintigraphy is not predictive of late cardiac complications in patients with Hodgkin's disease treated with mediastinal radiation

PURPOSE

To assess whether abnormalities depicted by Thallium-201 scintigraphy can predict the occurrence of late cardiac complications in patients with Hodgkin's disease treated with mantle field radiation therapy.

METHODS AND MATERIALS

Thallium scintigraphy was performed in 49 patients at a median of 75 months after initial treatment (range 28-208 months). Initial treatment consisted in chemotherapy, given to two-thirds of the patients and mantle field radiation, delivered to all patients, using a 25-MV linear accelerator. Myocardial perfusion defects were observed in 78% of patients on thallium scintigraphy. These patients had their cardiac status reassessed at a median follow-up of 13.5 years after treatment.

RESULTS

Forty-two patients were assessable, as data on the cardiac status were missing in 7 patients. The majority of patients received at least 40 Gy, and 75% of them were treated with one field per day. The median follow-up of patients is 13.5 years (range 9-24.5). Eleven cardiac complications were observed in 9 patients (coronary artery disease [n = 2], conduction-system abnormalities [n = 3], valvular defects [n = 5], and congestive heart disease [n = 1]). The median 15-year actuarial incidence of cardiac complications was 21% (95% confidence interval of 9-40%). The positive and negative predictive value of thallium scintigraphy was 19% and 77%, respectively. The univariate analysis showed that the extent of left ventricle exposure to irradiation was an adverse prognostic factor, and chemotherapy administered before mantle field irradiation was of borderline significance.

CONCLUSION

Thallium scintigraphy is not predictive of late cardiac complications. The extent of left ventricle exposure to radiation and possibly chemotherapy given before radiation treatment are adverse prognostic factors.

[Mechanism of laser radiation action at tissue and cellular levels]

The paper describes the action of low-intensity laser radiation (LILR) and high-intensity one (HILR) on biological tissues. LILR produces its action on cells by changing the membranous formations-receptors and ion channels. At cardiac surgery, HILR stimulates uncontractile myocardial elements, by inducing the secretion of biologically active substances and the activation of enzyme systems that ensure the implementation of neoangiogenesis in the ischemic myocardium.

A photothrombotic ring stroke model in rats with sustained hypoperfusion followed by late spontaneous reperfusion in the region at risk

In clinical thromboembolic stroke, spontaneous late recanalization is a common feature, but one which has been very sparsely studied experimentally. This study aimed at enabling the study of spontaneous reperfusion and exploring its consequences by modifying a recently developed photothrombotic-stroke model that focuses on the region-at-risk located within an ischemic ring-locus. The exposed crania of male Wistar rats (280-340 g) were subjected to a ring-shaped (5.0 mm outer diameter and 0.35 mm thick) laser-irradiation beam (514.5 nm; 0.89 W/cm2) for 2 min simultaneously with intravenous erythrosin B (17 mg/kg) infusion for 30 s. Transcardial carbon-black perfusion experiments revealed a ring-shaped cortical perfusion deficit at 4 h post-irradiation, which progressively increased at 10, 24, and 48 h, at which time the whole region-at-risk was pale with single distal branches of the middle cerebral artery being extensively narrowed, but not occluded. At 72 h, spontaneous reperfusion was observed in the region-at risk, which was even more pronounced at 7 and 28 days. Cortical cerebral blood flow (cCBF), measured by laser-Doppler flowmetry, was distinctly reduced at 2 min post-irradiation and further decreased slightly during 4 h of recording to ca. 24% of baseline values at the ring locus and 40% in the region-at-risk. In the region-at-risk, cCBF flow values were 23-30% of the baseline at 2448 h post-irradiation, followed by a relative cCBF increase to 71 and 77% at 72 and 96 h post-irradiation. Brain water content in the ischemic part of the cortex increased steadily from 4 to 48 h post-irradiation; at 72 h, it leveled off and returned to control values at 7 days. In conclusion, by employing a laser beam in the shape of a thin ring, critically sustained cCBF reduction was followed by late, consistent spontaneous reperfusion in the region-at-risk in this novel photochemically induced stroke-in-evolution model.

Microwave ablation of myocardial tissue: the effect of element design, tissue coupling, blood flow, power, and duration of exposure on lesion size

INTRODUCTION

The biophysical properties of microwave electromagnetic radiation suggest that it may be an alternative to radiofrequency (RF) energy for ablation of arrhythmias resistant to treatment using RF ablation.

METHODS AND RESULTS

The aim of this study was to characterize lesions produced using simple element designs in a blood superfused ovine tissue model to simulate endocardial ablation. The effect of tissue bath flow, duration of microwave exposure, and changes in forward power on lesion size were examined using a modified monopole element. Lesion size increased with increasing duration of exposure and increasing forward power (P < 0.05). Lesion depth was 0.7+/-0.7 mm after 30 seconds and 11.5+/-1.9 mm after 360 seconds. Lesion depths at 61, 71, and 80 W were 6.4+/-3.7, 8.9+/-2.0, and 11.9+/-1.2 mm, respectively. Altering flow within the bath from 3 to 5 L/min did not significantly change lesion size.

CONCLUSION

Simple element designs can be used to produce a range of lesions from very small sizes to lesions that are transmural in the ventricle. The temperature half-time for microwave ablation is far greater than that of RF ablation. Like RF lesions, the lesions produced by microwave ablation have greater width than depth. Deep penetration of lesions into the ventricular myocardium can only be achieved with these elements by producing lesions of perhaps unnecessarily large volume.

Does blood flow through holmium:YAG transmyocardial laser channels?

BACKGROUND

Early reports indicate that transmyocardial laser revascularization improves symptoms in patients with refractory angina. However, there is little experimental evidence of whether blood flow through channels is the mechanism of action.

METHODS

Endocardial channels were made in the distribution of the left anterior descending coronary artery in canine hearts (n = 5) using a holmium:yttrium-aluminum garnet laser. Hearts were excised acutely while perfused in a retrograde fashion from a second dog so that the aortic valve always remained closed. The proximal left anterior descending coronary artery was ligated. To measure direct transmyocardial blood flow, colored microspheres were injected into the left ventricular chamber.

RESULTS

The number of spheres per gram of tissue in the channel region was significantly higher than in the control region (low load, 302.5 +/- 169.0 versus 41.8 +/- 59.4; high load, 208.4 +/- 138.3 versus 5.8 +/- 11.7; both, p < 0.05). However, the estimated regional blood flow through the channels was extremely low (<0.01 mL/g/min. In the chronic setting (n = 4) (2-week survival), no flow as detected through the channels, and the endocardial entry points were closed.

CONCLUSIONS

Transmyocardial blood flow does not appear to occur through channels made with the holmium:yttrium-aluminum garnet laser. It remains to be determined whether this is the case with other types of lasers.

Mechanisms of coronary hyperconstriction in response to serotonin induced by X-irradiation in miniature pigs: increased constrictive response of medial smooth muscle

Experimental and clinical studies suggest that X-irradiation to the coronary artery may enhance vasoconstrictive response. This study aimed to clarify the effect of X-irradiation on the vasomotor response of porcine coronary artery. X-ray (15 Gy) was selectively irradiated to the left anterior descending coronary artery (LAD) in 14 Göttingen miniature pigs. The coronary vasomotor responses to serotonin at the irradiated site (LAD) and the control site (the left circumflex artery; LCX) were assessed by quantitative arteriography before and 1 h and 1, 2, and 4 weeks after X-irradiation. At 2 weeks, endothelium-dependent vasodilation in response to substance P was also evaluated arteriographically in vivo. At 2 weeks, isometric tension studies were performed to evaluate the constrictive responses of medial muscle strips and endothelium-dependent relaxation. Coronary vasoconstriction in response to serotonin was enhanced 1 week after, and further augmentation was noted 2 and 4 weeks after X-irradiation. Endothelium-dependent vasodilation in response to substance P in vivo was preserved 2 weeks after X-irradiation. Coronary arteriography showed no organic stenosis at the irradiated site. In vitro studies demonstrated that medial muscle strips of the irradiated site showed hypercontraction in response to serotonin and that endothelium-dependent relaxation in response to serotonin and substance P was preserved at the irradiated site. A histological study revealed no appreciable changes of the endothelial cells or intimal thickening.(ABSTRACT TRUNCATED AT 250 WORDS)

[Changes in intracellular regeneration and the indices of endocrine function and cardiac microcirculation in exposure to decimeter waves]

An electron-microscopic study of rabbit heart with experimental myocardial infarction revealed that extracardiac exposure to decimetric waves (DW) activated intracellular regeneration in the myocardium. This was associated with enhanced circulation and endocrine activity in the heart. Most pronounced regeneration was registered in adrenal exposure, the effect of the parietal exposure being somewhat less.

[The adrenergic regulation of cardiomyocyte electrophysiological activity, cardiac biochemical function and coronary blood flow in rats with incorporated 131I]

The study was made of the rat heart isolated according to Langendorf and right auricles. Intraperitoneal injections of 2.5 MBq/kg 131I were performed. Electrophysiological and biomechanical myocardium response to stimulation of alpha and beta-adrenoreceptors with isoprenalin and phenylephrine hydrochloride was analyzed. Postradiation modification of adrenergic control in animals with incorporated 131I appeared as reduced functional response of cardiomyocytes and intact heart to beta-adrenoagonist and enhanced response to alpha-agonist was detected.

In vitro assessment of cardiac performance after irradiation using an isolated working rat heart preparation

The effect of irradiation on cardiac function was assessed using an isolated working rat heart preparation. The animals were given single doses of X-rays in the range 15-30 Gy to their hearts. Cardiac output (CO = aortic flow + coronary flow), heart weight and body weight were followed for a period of 10 months after treatment. Irradiation led to a decrease in cardiac function. This reduction was dose-dependent and progressive with time after treatment. The shape of the Frank-Starling curves constructed for irradiated hearts suggests a loss of contractile function of the myocardium. Coronary flow rates measured in 'working' hearts and in 'Langendorff' hearts were not significantly changed by the irradiation treatment. The isolated working rat heart preparation proved to be a simple and suitable animal model for the investigation of irradiation-induced cardiotoxicity.

Radiation effects on left ventricular function and myocardial perfusion in long term survivors of Hodgkin's disease

We evaluated systolic and diastolic indices of left ventricular performance by radionuclide angiocardiography and myocardial perfusion with exercise/rest thallium scintigraphy in 16 patients previously irradiated for Hodgkin's disease. These commonly used indices of left ventricular (LV) performance included LV ejection fraction (LVEF) as a measure of systolic function, and LV peak filling rate (PFR) as a measure of diastolic function. The presence of coronary artery disease (CAD) was evaluated by ECG treadmill testing (13 patients) and by quantitative planar thallium scintigraphy (12 patients). Patients were 16-38 years old (mean 24.9 +/- SD 6.2) at the tim eof irradiation, and were evaluated 2.5-21.5 years (mean 9.3 +/- 6.3) after radiation therapy (RT). RT was delivered with beam energies of 2-18 MV, equally weighted AP-PA mantle fields with both fields treated daily for most patients (13 patients), and fraction sizes of 1.5-2.0 Gy. Six patients received radiation to th entire cardiac volume, most commonly via left-sided partial transmission lung blocks (PTLB). Patient data were analyzed according to the volume of heart treated. Individuals who had the entire cardiac volume irradiated were assigned to group I (N = 6), and those patients who had some portion of the heart shielded throughout treatment comprised group II (N = 10). In this series, no perfusion defects were evident in either group by quantitative planar thallium scintigraphy. Mean LVEF for all patients studied was 60% (normal LVEF greater than or equal to 50%). Patients in group I had a lower mean LVEF than those in group II, 55 +/- 4% versus 63 +/- 6% (p = 0.01). Mean PFR for all patients studied was normal at 3.5 EDV/sec (normal PFR greater than or equal to 2.54 EDV/sec). Patients in group I had a lower mean PFR than those in group II, 3.0 +/- 0.6 vs 3.8 +/- 0.7 EDV/sec (p = 0.04). Thus, patients irradiated to large cardiac and pulmonary volumes had lower LVEF and PFR within the normal range compared to patients who had some portion of the cardiac volume shielded. These differences are statistically significant in the relatively small groups studied but do not appear to be associated at the present time with clinically significant effects.

Morphological and functional changes in the rat heart after X irradiation: strain differences

The hearts of mature male rats of the Wistar and Sprague-Dawley strains were locally irradiated with single doses of 17.5 and 20.0 Gy of X rays, respectively. These two dose levels had previously been shown to result in a comparable latent period between irradiation and the death of rats of these two strains from cardiac failure. Morphological changes in the myocardium and modifications in cardiac function were assessed in the animals at 28, 70, and 100 days after irradiation. The first radiation-induced change which was observed in the myocardium was a rapid decline in capillary density and a loss of alkaline phosphatase activity by the capillary endothelial cells. The capillary density was reduced to approximately 50% of that of unirradiated control values at 28 days and to approximately 40% of the control values between 70 and 100 days after irradiation. The loss of enzyme activity was also detected at 28 days. Examination of histological sections showed an increase by 70 days in the areas with negative enzyme activity up to approximately 70% of the myocardium. The reduction in capillary density and the loss of enzyme activity occurred before any marked pathological changes were seen in the myocardium. The pathological lesions seen in the myocardium at 100 days after irradiation were qualitatively and quantitatively the same in the two strains of rat. Measurements of cardiac output in Sprague-Dawley rats showed a gradual decline in output after irradiation; however, measurements in Wistar rats showed a progressive increase in cardiac output over the same period of time. It was shown by rubidium extraction that there was an increase in the percentage of the total cardiac output distributed to the ventricular muscle of Sprague-Dawley rats, while similar measurements in Wistar rats showed no significant change. In spite of the marked strain differences observed in cardiac output and rubidium extraction, blood perfusion per gram of ventricular muscle was apparently not modified in both strains of rat after irradiation. These findings indicated that the correlation between morphological effects after irradiation and the functional expression of damage is highly complex.

Vascular complications of thorium dioxide

Vascular complications occurring late after exposure to thorium dioxide (thorotrast) are described in two patients. One patient had both cerebral andmyocardial infarcts and died at age 25 years. Necropsy disclosed both adventitial and intimal fibrosis of the left carotid artery and greater than 75 per cent cross-sectional area luminal narrowing of both the left main and left anterior descending coronary arteries. The other patient, a 33 year old man, had no cerebral symptoms in life but total obstruction of the right carotid artery secondary to a thorotrastoma was found at necropsy. Vascular complications due to thorotrast appear to represent consequences of chronic alpha irradiation.