Polymorphic ventricular tachycardia in patients with vasospastic angina--clinical and electrocardiographic characteristics and long-term outcome

There have been few clinical studies exploring the characteristics of spontaneous polymorphic ventricular tachycardia (VT) during a vasospastic angina attack. During a 4-year recruitment period, Holter ECG recordings were monitored for 42+/-24 h during a drug-free period in 60 consecutive patients with vasospastic angina (VSA) and of these, 8 patients had at least one episode of polymorphic VT during monitoring. Ischemic ST segment elevation was immediately preceded the spontaneous polymorphic VT in all 8 patients, 4 of whom had silent coronary vasospasm. Immediately before the onset of polymorphic VT, both R-on-T and long-short sequences were observed in 4 of the 8 patients and ST wave alternans were recorded in 2 patients. VT exhibited a pattern of torsade de pointes in 4 of the 8 patients. Five patients underwent electrophysiologic testing during a drug-free asymptomatic phase, and polymorphic VT was induced in 2 of the 5 patients, with one developing ventricular fibrillation. During a follow-up period of 73+/-17 months, there was a significant difference in the incidence of sudden death between patients with and without VT (2/8 cases [25%] vs 0/52 [0%]; p<0.01). Thus, vasospastic attacks, even if asymptomatic, that immediately precede the development of polymorphic VT may be associated with a repolarization abnormality and an increased risk of sudden death.

Assessment of noninvasive markers in identifying patients at risk in the Brugada syndrome: insight into risk stratification

OBJECTIVES

The aim of this study was to compare the use of various noninvasive markers for detecting risk of life-threatening arrhythmic events in patients with Brugada syndrome.

BACKGROUND

The role of conduction disturbance in arrhythmogenesis of the syndrome is controversial, whereas it is well established that repolarization abnormalities are responsible for arrhythmias. The value of noninvasive markers reflecting conduction or repolarization abnormalities in identifying patients at risk for significant arrhythmias has not been shown.

METHODS

We assessed late potentials (LP) using signal-averaged electrocardiography (ECG), microvolt T-wave alternans (TWA), and corrected QT-interval dispersion (QTD) in 44 consecutive patients who had ECGs showing a pattern of right bundle branch block and ST-segment elevation in leads V1 to V3 but structurally normal hearts. The patients were compared with 30 normal individuals.

RESULTS

Eleven patients were excluded from data analysis because of an absence of ECG manifestations of Brugada syndrome at the time of the tests. A history of life-threatening events defined as syncope and aborted sudden death was present in 19 of 33 patients (58%); in 15 of the 19 patients, stimulation induced ventricular fibrillation or polymorphic ventricular tachycardia. The LP were present in 24 of 33 patients (73%); TWA were present in 5 of 31 patients (16%); and a QTD >50 ms was present in 9 of 33 patients (27%). The incidence of LP in Brugada patients was significantly (p < 0.0001) higher than in the controls, whereas incidences of TWA and QTD were not significantly different. Multivariate logistic regression analysis revealed that the presence of LP had the most significant correlation to the occurrence of life-threatening events (p = 0.006).

CONCLUSIONS

Late potentials are a noninvasive risk stratifier in patients with Brugada syndrome. These results may support the idea that conduction disturbance per se is arrhythmogenic.

Correlation of genetic etiology with response to beta-adrenergic blockade among symptomatic patients with familial long-QT syndrome

Mutations in any of the five genes KCNQ1, KCNH2, KCNE1, KCNE2, and SCN5A can be responsible for familial long QT syndrome (LQTS), an arrhythmogenic disorder that entails a high risk of sudden death. beta-Adrenergic blocking agents are the first therapeutic choice, and 80% of patients treated with these agents show symptomatic relief; however the remaining 20% do not respond well. We previously performed a nationwide analysis of familial long QT syndrome (LQTS) in Japan and identified 32 mutations in the KCNQ1 and KCNH2 genes. In the present retrospective study, we found that patients carrying mutations in the KCNQ1 gene responded better to beta-adrenergic blocking agents than those with KCNH2 mutations (12 of 13 vs 1 of 5; P = 0.0077, Fisher's exact test). This is a good example of the power of genetic diagnosis to direct the selection of appropriate therapy for patients with diseases of heterogeneous genetic etiology.

Diagnosis of carotid artery atheroma by magnetic resonance imaging

Atheroma appears as a very low signal intensity area on 2-dimensional time-of-flight (TOF) magnetic resonance (MR) images, and its components have various signal intensities on spin-echo (SE) images. The present study investigated atheroma of the carotid arteries in 37 subjects with risk factors (63+/-10 years of age; 19 men) by magnetic resonance imaging (MRI). On 2-dimensional (2D) TOF images, the carotid arteries were clearly demonstrated in all cases and atheroma was detected in 23 patients. The most common location of atheroma was at the origin of the internal carotid artery. There was vascular remodeling in all patients with atheroma. 2D-TOF images showed 97% agreement with ultrasonography. SE images clearly demonstrated atheroma in all 23 patients with atheroma. All patients with atheroma showing high signal intensity on T1-weighted images had hyperlipidemia. These findings indicate that the 2D-TOF imaging method is useful for detecting atheroma and SE-images are useful for its characterization.

Evaluation of flow volume and flow patterns in the patent false lumen of chronic aortic dissections using velocity-encoded cine magnetic resonance imaging

In 21 patients with chronic aortic dissections and proven patent false lumens, the flow volume and flow patterns in the patent false lumens was evaluated using velocity-encoded cine magnetic resonance imaging (VENC-MRI) and the relationship between the flow characteristics and aortic enlargement was retrospectively examined. Flow patterns in the false lumen were divided into 3 groups: pattern A with primarily antegrade flow (n=6), pattern R with primarily retrograde flow (n=3), and pattern B with bidirectional flow (n=12). In group A, the rate of flow volume in the false lumen compared to the total flow volume in true and false lumens (%TFV) and the average rate of enlargement of the maximum diameter of the dissected aorta per year (deltaD) were significantly greater than in groups R and B (%TFV: 74.1+/-0.07 vs 15.2+/-0.03 vs 11.8+/-0.04, p<0.01; deltaD: 3.62+/-0.82 vs 0 vs 0.58+/-0.15 mm/year, p<0.05, respectively). There was a significant correlation between %TFV and deltaD (r=0.79, p<0.0001). Evaluation of flow volume and flow patterns in the patent false lumen using VENC-MRI may be useful for predicting enlargement of the dissected aorta.

A novel SCN5A mutation associated with idiopathic ventricular fibrillation without typical ECG findings of Brugada syndrome

Mutations in the human cardiac Na+ channel alpha subunit gene (SCN5A) are responsible for Brugada syndrome, an idiopathic ventricular fibrillation (IVF) subgroup characterized by right bundle branch block and ST elevation on an electrocardiogram (ECG). However, the molecular basis of IVF in subgroups lacking these ECG findings has not been elucidated. We performed genetic screenings of Japanese IVF patients and found a novel SCN5A missense mutation (S1710L) in one symptomatic IVF patient that did not exhibit the typical Brugada ECG. Heterologously expressed S1710L channels showed marked acceleration in the current decay together with a large hyperpolarizing shift of steady-state inactivation and depolarizing shift of activation. These findings suggest that SCN5A is one of the responsible genes for IVF patients who do not show typical ECG manifestations of the Brugada syndrome.

[Treatment of choice and long-term prognosis for ventricular arrhythmias]

Treatment of choice and long-term prognosis of the patients with ventricular arrhythmias are described in terms of prevention of sudden cardiac death and/or recurrence of life-threatening arrhythmias(ventricular tachycardia and ventricular fibrillation). 1) As to the long-term prognosis of ventricular tachyarrhythmias, presence of organic heart disease and degree of cardiac dysfunction are major determining factors. 2) The prognosis of patients with ventricular arrhythmias depends on how sudden cardiac death and life-threatening arrhythmias can be prevented. Among various methods, the electrophysiological test and its guided-therapy for antiarrhythmic drugs are now believed to be the most effective method for the prediction and prevention of the life-threatening events. We propose that the signal averaged electrocardiography is the best screening method as non-invasive approach for the selection of patients undergoing the electrophysiological test. 3) There are still certain limitations as to the prediction of sudden cardiac death and/or prevention of recurrent life-threatening arrhythmias by antiarrhythmic drug treatments in the certain numbers of patients depending on their basal cardiac disease and functional impairment. At present, catheter ablation procedure and implantable cardioverter defibrillator are the choice of the treatment in these cases. 4) In addition to conventional antiarrhythmic drugs, the treatment for the basal cardiac condition is mandatory for the long-term prognosis in the patients with ventricular arrhythmias.

Voltage-shift of the current activation in HERG S4 mutation (R534C) in LQT2

OBJECTIVE

Recently, a novel missense mutation (R534C) in the S4 region of human ether-a-go-go-related gene (HERG) was identified in one Japanese LQT2 family. The S4 region presumably functions as a voltage sensor. However, it has not yet been addressed whether the S4 region of HERG indeed functions as a voltage sensor, and whether these residues play any role in abnormal channel function in cardiac repolarization.

METHODS

We characterized the electrophysiological properties of the R534C mutation using the heterologous expression system in Xenopus oocytes. Whole cell currents were recorded in oocytes injected with wild-type cRNA, R534C cRNA, or a combination of both.

RESULTS

Clinical features--QTc intervals of all affected patients with R534C mutation in HERG are prolonged ranging from 460 to 680 ms (averaged QTc interval > 540 ms). One member of this family had experienced sudden cardiac arrest, and other suffered from recurrent palpitation. Electrophysiology--Oocytes injected with R534C cRNA did express functional channels with altered channel gating. Kinetic analyses revealed that the R534C mutation shifted the voltage-dependence of HERG channel activation to a negative direction, accelerated activation and deactivation time course, and reduced steady-state inactivation. Quantitative analyses revealed that this mutation did not cause apparent dominant-negative suppression. Computer simulation--Incorporating the kinetic alterations of R534C, however, did not reproduce prolonged action potential duration (APD).

CONCLUSIONS

The data revealed that arginine at position 534 in the S4 region of HERG is indeed involved in voltage-dependence of channel activation as a voltage sensor. Our examination indicated that HERG current suppression in R534C mutation was the least severe among other mutations that have been electrophysiologically examined, while affected patients did show significant QT prolongation. This suggest that another unidentified factor(s) that prolong APD might be present.

[The effects of propofol anesthesia with or without the use of nitrous oxide on the intraoperative involuntary movement, the postoperative awareness and vomiting]

The authors investigated the effect of anesthesia with nitrous oxide and propofol on intraoperative involuntary movement, muscle relaxant usage, postoperative nausea and vomiting, the total amount of propofol used, and recovery time from anesthesia. Eighty-eight patients for gynecological surgery were randomly divided into group PE: propofol/epidural (n = 44), and group PEG: propofol/epidural/nitrous oxide (n = 44). The frequency of postoperative nausea and vomiting were assessed at 24-h postoperatively by blinded observers. There were significant decreases of the mean amounts of propofol and muscle relaxant used between group PEG and group PE. The authors found no correlation between the use of nitrous oxide and intraoperative involuntary movement, subsequent development of postoperative quality of awareness, recovery time, nausea and vomiting. We recommend PEG method for gynecological surgery rather than PE from an economical viewpoint because it is associated with the reduction of mean propofol and muscle relaxant used.

Non-dipolarity of heart potentials estimated by magnetocardiography in normal subjects

We studied non-dipolarity characteristics during ventricular excitation in normal adults and children by magnetocardiography (MCG) by recording magnetic field on the thorax. The source and currents of the electrical dipole from the onset up to 60 ms of ventricular excitation were analyzed in 16 adults and 5 children. A single equivalent current dipole (ECD) was estimated by Sarvas' formula for the sphere model at 1 ms intervals. The non-dipole value (NDV) was calculated from the magnetic field strength at each recording point and theoretically estimated by ECD, representing an index for the non-dipolarity. At 32-34 ms from the beginning of QRS, the mean NDV was a minimum in all subjects suggesting at least a non-dipole component during this period. High NDV (over 5%) were present in most subjects in both the early and late phase compared to this period. Thirteen of 16 adults had a high NDV in the early phase (9.3 +/- 3.0%, mean +/- SD) and all 16 subjects had a high NDV in the late phase (21.5 +/- 10.5%). All 5 children had high NDV in both the early (10.5 +/- 5.4%) and late phases (16.8 +/- 7.9%). A single ECD estimation by MCG showed a relatively low non dipolar component and MCG could be applied to the clinical evaluation of cardiac excitation in both normal and pathological conditions.

Significance of abnormal root mean square voltages in signal averaged electrocardiogram as a reliable predictor of sustained ventricular tachycardia

The late potential is useful to predict patients with sustained ventricular tachycardia (VT). However, because positive predictive value for sustained VT is low, the validity of late potential for screening the patients to be studied by electrophysiological tests was not high. We examined 923 cases, including 63 cases of sustained VT. When we separated patients showing abnormal values of the root mean square voltage of the QRS end part 40 milliseconds (RMS40) into four groups, there was a tendency of a higher incidence of sustained VT with lower value of RMS40. When we conducted electrophysiological tests on 121 cases without sustained VT, it turned out a high induction rate of sustained VT in patients with low RMS40 values (RMS40 < 10 microV, 67%; < 20 microV, 30%; 20 microV, < or = 5%). We conclude abnormally low value (less than 10 microV) of RMS40 can be useful for screening the late potential-positive cases who are high risk for inducible sustained VT.

Genomic organization and mutational analysis of HERG, a gene responsible for familial long QT syndrome

Familial long QT syndrome (LQTS) is characterized by prolonged ventricular repolarization. Clinical symptoms include recurrent syncopal attacks, and sudden death may occur as a result of ventricular tachyarrhythmias. Three genes responsible for this syndrome (KVLQT1, HERG, and SCN5A) have been identified so far, and mutations have been reported on the basis of partially characterized genomic organization. To optimize the search for HERG mutations, we have determined the genomic structure of HERG and investigated mutations in LQTS families. Human genomic clones containing the HERG gene were isolated from a human genomic library by using reverse-transcribed polymerase chain reaction (RT-PCR) products from this gene as probes. We determined exon/intron boundaries and flanking intronic sequences by using primers synthesized on the basis of the HERG cDNA sequence available in the DNA database. HERG was shown to consist of 15 exons spanning approximately 19 kb on chromosome 7q35. Subsequently, we synthesized oligonucleotide primers to cover the entire coding region and searched for mutations in 36 Japanese LQTS families. When genomic DNA from each proband was examined by the PCR/single-strand conformation polymorphism technique followed by direct DNA sequencing, five novel mutations were detected. Each mutation was present in affected relatives of the respective proband. This work should increase the efficiency of screening mutations associated with HERG.

Supernormal conduction in a case of Mobitz type II atrioventricular block

A 52-year-old woman exhibited Mobitz type II atrioventricular block with right bundle branch block and 1:1 atrioventricular conduction at or slower than 80 beats/min. Electrophysiologic study revealed transient HV interval block followed by recovery from the block at shorter coupling intervals without prolongation of the H1H2 and H2V2 intervals, suggesting true supernormal conduction. Isoproterenol enhanced the supernormal conduction, with shortening of blocked intervals and recovery of atrioventricular conduction, while atropine caused their less marked enhancement. Linking (ie, retrograde concealment of the impulse to the distal His bundle region through the blocked right bundle branch) is considered a possible mechanism of supernormal conduction in this case.

Demonstration of Purkinje potential during idiopathic left ventricular tachycardia: a marker for ablation site by transient entrainment

During VT of QRS morphology with right bundle branch block and left axis deviation in a patient without obvious structural heart disease, entrainment by pacing from the right ventricular outflow tract and high right atrium was demonstrated. During entrainment of VT, a Purkinje potential preceding the QRS and recorded at the left ventricular mid-septum was activated by orthodromic impulses in the reentry circuit. The interval between the Purkinje potential and the earliest left ventricular activation was decrementally prolonged with shortening of pacing cycle length. Radiofrequency energy was applied to this site, resulting in successful elimination of VT. Therefore, the Purkinje potential represented activation by an orthodromic wavefront in the reentry circuit, while the orthodromically distal site to this potential showed an area of slow conduction with decremental property.

Increase in heart rate after radiofrequency catheter ablation is mediated by parasympathetic nervous withdrawal and related to site of ablation

To assess the mechanism for the increased sinus rate after radiofrequency catheter ablation performed for atrioventricular nodal reentrant tachycardia (AVNRT), we studied heart rate variability before and after radiofrequency catheter ablation in 17 patients with AVNRT and in 38 patients with an accessory pathway. The accessory pathway was located at the left ventricular free wall, the right ventricular free wall, or the posterior interventricular septum. An increased sinus rate was observed in patients with AVNRT or with the accessory pathway at the posterior septum or left free wall after radiofrequency ablation. In these groups, high-frequency power, root mean square of successive difference and percent of adjacent cycles that were more than 50 ms apart, all of which are indices reflecting parasympathetic nervous activity, were decreased. The ratio of low-frequency to high-frequency power reflecting sympathovagal balance, was increased in patients with AVNRT or with an accessory pathway at the posterior septum or left free wall. Increases in sinus rate were correlated with decreases in high-frequency power, and percent of adjacent cycles more than 50 ms apart that the increase in heart rate was due to parasympathetic nervous withdrawal.

[A case of giant hepatocellular carcinoma successfully treated by arterial administration of SMANCS]

A 68-year-old male was referred to our hospital for the precise examination of a giant hepatic tumor detected in a mass survey. The lesion occupied most of the right hepatic lobe, further advancing to the medial segment of the left lobe. However, hepatic functions were well preserved (ICG K = 0.141). Considering the characteristic images of the lesion with positive anti-HCV and high titer of PIVKA II (0.860 AU/ml), the diagnosis was hepatocellular carcinoma. First arterial administration of SMANCS was performed on May in 1994, followed by 6 successive procedures with an interval of about 2 months (total dosage 36 mg), resulting in remarkable tumor shrinkage and tumor marker normalization. On January in 1995, a metastatic lesion to the right rib was controlled by 2 mg of SMANCS administered to the intercostal artery combined with radiation therapy (60 Gray). Frequent administrations of SMANCS caused no serious complications, and tumor feeders were well preserved. Therefore, arterial administration of SMANCS is thought to be one choice for the therapy of giant HCC with good functional reserve.

Catheter ablation for the common type of atrioventricular nodal reentrant tachycardia

Radiofrequency (RF) catheter ablation of the slow AV nodal pathway was attempted in 34 patients with common type of AV nodal reentrant tachycardia (AVNRT). Radiofrequency energy of 18-32 watts was applied for 30-60 seconds at sites exhibiting atrial-slow pathway potentials or slow potentials. These potentials were recorded at the mid or posterior septum, anterior to the coronary sinus ostium. A mean of two radiofrequency applications successfully eliminated AVNRT in all patients. The incidence of junctional ectopy was significantly higher during 34 effective applications of radiofrequency energy than during 36 ineffective applications (100% versus 17%). Thus, the recording of atrial-slow pathway potentials or slow potentials, and the development of junctional ectopy can be used as a marker for successful ablation. Slow AV nodal conduction was eliminated in 22 patients and persisted without inducible AVNRT in 12. None of the patients had recurrences of AVNRT over a mean follow-up interval of 12 months, and all had preserved AV conduction. Long-term follow-up studies with an electrophysiological method confirmed that the ablation was effective. Transient AV block was observed in only 1 patient, and no major complications were noted. Thus, radiofrequency catheter ablation of the slow AV nodal pathway is highly effective and safe, with a low rate of complication, for the treatment of common type of AVNRT.

Malignant fibrous histiocytoma of the esophagus

A 78-year-old man presented with an esophageal polyp that was confirmed by immunohistochemistry and electron microscopy to be malignant fibrous histiocytoma. The tumor was comprised of a proliferation of spindle-shaped cells admixed with bizarre giant cells. These tumor cells were immunoreactive for smooth muscle actin, vimentin, alpha-1-anti-chymotrypsin and CD68. Electron microscopic examination revealed the myofibroblastic and histiocytic features of the tumor cells. No elements of epithelial or myogenic differentiation were found in the tumor. Malignant fibrous histiocytoma of the esophagus is extremely rare, with 10 cases being documented so far in the literature. The differential diagnosis of pleomorphic tumors of the esophagus is discussed.

Induction of polymorphic ventricular tachycardia by programmed ventricular stimulation in vasospastic angina pectoris

This study was designed to examine the ventricular vulnerability of patients with vasospastic angina. Fourteen patients (mean age 57 +/- 9 years) with vasospastic angina underwent electrophysiologic testing during the asymptomatic phase (baseline) and after the relief of acetylcholine-induced spasm with isosorbide dinitrates. Twenty patients without structural heart disease served as a control group. By programmed ventricular stimulation, polymorphic ventricular tachycardia (VT) was induced at baseline in 6 of 14 patients, with 1 patient developing ventricular fibrillation and 7 of 14 patients developing repetitive ventricular responses. After isosorbide dinitrate, polymorphic VT was induced in only 1 patient who had ventricular fibrillation at baseline. Repetitive ventricular responses were induced in 3 of 5 patients who had VT at baseline and in 4 of the 7 patients with repetitive ventricular responses at baseline. There was a significant difference in the incidences and severity of induced ventricular arrhythmias between the 2 phases (p <0.01). Among 20 control subjects, repetitive ventricular responses were induced only in 6 patients, but no VT was induced. There was a significant difference in the incidence of induced ventricular arrhythmias and VT at baseline between the vasospastic angina and control groups (p <0.001 and <0.01, respectively). Thus, patients with vasospastic angina had increased ventricular vulnerability, even during the symptom-free period without ischemic events, which could predispose to the development of life-threatening arrhythmias aggravated by vasospastic attacks.

[Tricuspid and mitral regurgitation due to congenital hypoplasia of atrioventricular valves in the aged: a case report]

A 76-year-old woman with a history of repeated right-sided cardiac failure during the past 2 years presented with tricuspid and mitral regurgitation due to congenital hypoplasia of atrioventricular valves. Two-dimensional echocardiography demonstrated enlarged right atrium and right ventricle, and discoaptation between the leaflets. Color Doppler echocardiography revealed severe tricuspid regurgitation through the gap between the leaflets. Autopsy showed congenital hypoplasia of the leaflets and the chordae tendineae in the tricuspid and mitral valvular apparatus.

A case of cardiac sarcoidosis with remarkable atrophy of the left ventricular septum on two-dimensional echocardiography

Sarcoidosis is a multisystem granulomatous disorder of unknown etiology which mainly affects the lungs, skin, the lymphoreticular system, and the heart. We report a case of cardiac sarcoidosis in which a remarkably thin ventricular septum was demonstrated on two-dimensional echocardiography.

Long-term follow-up of the reproducibility of carotid sinus hypersensitivity in patients with carotid sinus syndrome

The reproducibility of carotid sinus hypersensitivity to carotid sinus massage was studied in the long-term follow-up of 8 patients with carotid sinus syndrome. A cardioinhibitory response was induced in 7 patients, while a vasodepressor response was found in the remaining patient. The 7 patients were treated with dual-chamber pacemaker implantation and the remaining patient was treated with propranolol. All of the patients remained asymptomatic during a follow-up period of 48 +/- 11 months. Carotid sinus massage during the follow-up period in patients with a cardioinhibitory response revealed asystolic intervals of 3 s or longer in 4 patients and in 3 patients at the second and third follow-up examinations, respectively, although there were no significant differences in the ventricular asystolic intervals between before, and 34 +/- 11 months and 48 +/- 11 months after treatment. However, each patient showed a wide variation in asystolic intervals. The differences in asystolic intervals between prior to treatment (first) and the third test were significantly greater than those between the first and the second test (2.4 +/- 1.2 s vs 0.7 +/- 0.6 s; p < 0.05). The one patient with a vasodepressor response had a decreased systolic blood pressure greater than 50 mmHg by carotid sinus massage at all three occasions. In conclusion, most patients with carotid sinus syndrome showed abnormal and variable responses to carotid sinus massage during long-term follow-up period although there was no recurrence of symptoms after treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Generation of active oxygens, cell deformation and membrane potential changes upon UV-B irradiation in human blood cells

The generation of peroxides (presumably hydrogen peroxide) by UV-B irradiation of human blood cells was detected. Non-fluorescent dihydrorhodamine 123 (DHR) is oxidized to fluorescent rhodamine 123 (R123) by H2O2 or peroxides with a stoichiometry of 1:1 in the presence of exogeneous peroxidase, and the fluorescence of R123 within the cells was measured using flow-cytometry. UV irradiation gave rise to changes in the cellular volume and the membrane potential, whose extent and direction were dependent on the type of blood cells. The production of peroxides (H2O2) in polymorphonuclear leukocytes is the largest among blood cells at the lower dose (< 0.1 J/cm2), and the production decreases with an increase in the dose, while the production in platelets is the smallest at the lower dose, but above 0.4 J/cm2 it increases suddenly so that at the higher dose (1.2 J/cm2) it amounts to 3.3 x 10(-16) mol/cell. For monocytes and lymphocytes, the production increases gradually with the increase in the dose.