An arrhythmia classification system based on the RR-interval signal

OBJECTIVE

This paper proposes a knowledge-based method for arrhythmic beat classification and arrhythmic episode detection and classification using only the RR-interval signal extracted from ECG recordings.

METHODOLOGY

A three RR-interval sliding window is used in arrhythmic beat classification algorithm. Classification is performed for four categories of beats: normal, premature ventricular contractions, ventricular flutter/fibrillation and 2 degrees heart block. The beat classification is used as input of a knowledge-based deterministic automaton to achieve arrhythmic episode detection and classification. Six rhythm types are classified: ventricular bigeminy, ventricular trigeminy, ventricular couplet, ventricular tachycardia, ventricular flutter/fibrillation and 2 degrees heart block.

RESULTS

The method is evaluated by using the MIT-BIH arrhythmia database. The achieved scores indicate high performance: 98% accuracy for arrhythmic beat classification and 94% accuracy for arrhythmic episode detection and classification.

CONCLUSION

The proposed method is advantageous because it uses only the RR-interval signal for arrhythmia beat and episode classification and the results compare well with more complex methods.

Ventricular pre-excitation in the general population: a study on the mode of presentation and clinical course

OBJECTIVE

To describe the mode of presentation and the clinical course of patients with ventricular pre-excitation (Wolff-Parkinson-White (WPW) syndrome), with special emphasis on asymptomatic cases in the general population.

METHODS

Over an eight year period (1990-97) a prospective population based survey of cases with WPW pattern was conducted in a defined population in north west Greece (340 000 inhabitants). ECGs with WPW pattern were obtained from a widespread pool of ECGs within the health system.

RESULTS

During the study period, 157 cases with WPW pattern were identified (49 female, 108 male). Ages ranged from infants to 84 years, mean (SD) 49.1 (21.0) years in female and 39.6 (20.6) years in male subjects (p < 0.01); 78 (49%) had no history of syndrome related symptoms. Asymptomatic subjects (n = 77; 24 female, 53 male) were older than symptomatic subjects (mean age 46.7 (21.0) v 38.5 (20.6) years, p < 0.03). Documented supraventricular tachycardia was recorded in 27 patients (17%) and atrial fibrillation in 12 (8%) (mean age at first episode 31.2 (18.3) and 51.6 (20.7) years, respectively, p < 0.01). During follow up (mean 55 months) no case of sudden death occurred. Three asymptomatic subjects reported episodes of brief palpitation.

CONCLUSIONS

WPW pattern is more common, and diagnosed at a younger age, in men than in women. About half the patients with WPW pattern on ECG are asymptomatic at diagnosis and tend to remain so thereafter. No sudden cardiac death occurred during the study period.

Outcome of patients with congestive heart failure treated with standard versus high doses of enalapril: a multicenter study. High Enalapril Dose Study Group

OBJECTIVES

We sought to prospectively and randomly compare survival with clinical and hemodynamic variables in patients with congestive heart failure (CHF) treated with standard versus high doses of enalapril.

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors produce hemodynamic and symptomatic benefits in patients with CHF, but there is still controversy about the optimal dose in this clinical setting.

METHODS

Two hundred and forty-eight patients with advanced CHF (age 56.3+/-12 years) were randomized to receive a maximal tolerated dose of enalapril, up to 20 mg/day in group 1 (mean dose achieved 17.9+/-4.3 mg/day, n = 122) and 60 mg/day in group 2 (mean dose achieved 42+/-19.3 mg/day, n = 126).

RESULTS

At enrollment, patients in group 1 were in New York Heart Association (NYHA) functional class 2.6+/-0.7 and had a mean systolic blood pressure (SBP) of 117+/-18 mm Hg, a mean heart rate (HR) of 85+/-16 beats/min and a left ventricular ejection fraction (LVEF) of 20.0+/-9.8%. In group 2, patients were in NYHA class 2.6+/-0.7; their SBP was 118+/-17 mm Hg, HR 83+/-15 beats/min and LVEF 18.8+/-8.1%. There were no significant differences in these characteristics between the two groups of patients at enrollment. After 12 months of follow-up, 22 (18%) of 122 patients in group 1 and 23 (18%) of 126 patients in group 2 had died (p = 0.995, with 80% power of the study to detect a delta difference of 13%). The NYHA class was the same (1.9+/-0.7) in both groups; SBP was 111+/-16 and 111+/-17 mm Hg, HR 77+/-12 and 79+/-13 beats/min and LVEF 31+/-19% and 30+/-12% in groups 1 and 2, respectively. These differences were not statistically significant. The study had a power of 80% to detect (p = 0.05) the following changes: 13% in death rate, 0.25 units in NYHA class, 6 mm Hg in SBP, 5 beats/min in HR and 6% in LVEF.

CONCLUSIONS

No significant differences were found in survival and clinical and hemodynamic variables between patients receiving standard and those receiving high doses of enalapril.

Maintenance of sinus rhythm after atrial defibrillation

The long-term results of 356 episodes of atrial defibrillation by DC shock carried out in 250 patients are reviewed. In 78 per cent of the cases, atrial fibrillation recurred by the end of 12 months in spite of the administration of quinidine or procainamide or propranolol, singly or combined. However, when no antidysrhythmic drugs were used the recurrence rate was higher at all periods of observation and 100 per cent at the end of 12 months. The difference in the overall results between the untreated group and the treated groups with the exception of the propranolol group is significant (p less than 0.05). In addition, the propranolol group showed an obviously reduced recurrence rate at 1 month, but afterwards the results tended to approximate those in the untreated group. The period during which sinus rhythm could be maintained in patients who underwent valve operations was on the whole the same as in patients who did not have heart surgery. However, in a small number of patients sinus rhythm was maintained for longer periods after mitral valve replacement than before it. Sinus rhythm was maintained for significantly longer periods when atrial fibrillation lasted less than 1 year than when it had been present for more than 1 year (p less than 0.001). It is concluded that there is justification for a judicious antidysrhythmic prophylaxis after atrial defibrillation.

PAF-acetylhydrolase activity of Lp(a) before and during Cu(2+)-induced oxidative modification in vitro

In human plasma with no detectable lipoprotein (a) (Lp(a)) levels, platelet-activating factor acetylhydrolase (PAF-AH) is associated with low density lipoprotein (LDL) and high density lipoprotein (HDL) with a distribution of 70 and 30%, respectively. We used a density gradient ultracentrifugation procedure to study the distribution of PAF-AH among lipoproteins in plasma containing Lp(a). Lp(a) was migrated as a broad band in the density region of d = 1.050-1.100 g/ml, independently of its isoform size. In plasma with Lp(a) levels 30-40 mg/dl or 80-100 mg/dl the PAF-AH activity migrated in this density region was 4 or 9% higher as compared to plasma having Lp(a) levels < 8 mg/dl (P < 0.05 or P < 0.02, respectively). Enrichment of plasma with the dense LDL5 subfraction, significantly increased the enzyme activity distributed in this density region. The physicochemical properties of the Lp(a)-associated PAF-AH activity were similar to those reported for the LDL-associated enzyme. However, the kinetic constants in small Lp(a) isoforms were significantly higher compared to large ones. Isoform F had apparent Km = 117 +/- 9 mumol/l and Vmax = 94 +/- 5 nmol/mg protein per min, and isoform S2/S3 had apparent Km = 36 +/- 9 mumol/l and Vmax = 25 +/- 5 nmol/mg protein per min. Removal of apolipoprotein (a) (apo(a)) from Lp(a) by reductive cleavage with dithiothreitol, slightly affected the amount of PAF-AH existing on Lp(a) since, only 15 +/- 5% of the total enzyme activity dissociated from its particle after density gradient ultracentrifugation. During Cu(2+)-induced Lp(a) oxidation, the PAF-AH activity decreased from 10.90 +/- 2.30 nmol/mg per min to 2.57 +/- 0.56 nmol/mg per min 4 h after the initiation of the oxidation (P < 0.001). The apparent Km of the enzyme remained essentially unchanged during oxidation, whereas Vmax was significantly decreased from 58.6 +/- 7.8 nmol/mg protein per min to 38.2 +/- 8.7 nmol/mg protein per min (P < 0.03). An extensive hydrolysis of the endogenous phosphatidylcholine (PC) to lysophosphatidylcholine (lyso-PC) was observed during Lp(a) oxidation, since the Lyso-PC/sphingomyelin molar ratio at the end of oxidation (0.55 +/- 0.09) was significantly higher than that before oxidation (0.19 +/- 0.01, P < 0.001). Our results show that the existence of Lp(a) in plasma alters the distribution of PAF-AH among the other lipoproteins. Apo(a) seems to affect the association of the enzyme with Lp(a) but does not bind itself to PAF-AH. During Lp(a) oxidation, the PAF-AH activity decreases whereas an extensive hydrolysis of the endogenous PC to Lyso-PC is observed which is possibly due to the PAF-AH activity.

Treatment of refractory unstable angina in geographically isolated areas without cardiac surgery. Invasive versus conservative strategy (TRUCS study)

AIMS

We compared invasive (on-site coronary angioplasty or emergency air-ambulance transfer for bypass grafting surgery) vs conservative (persistent medical treatment) strategies in the management of refractory unstable angina in geographically isolated hospitals without cardiac surgical facilities.

METHODS AND RESULTS

One hundred and forty eight randomized patients with refractory unstable angina were compared on an intention-to-treat basis. Outcomes (invasive vs conservative): (a) in hospital: stabilization (96% vs 43%, P=0.0001), non-fatal myocardial infarction (2.6% vs 4.2%, P=ns), death (1.3% vs 8.3%, P=0.046), combined outcome (3.9% vs 12.5%, P=0.053) and hospitalization (11.4+/-6.3 vs 12.4+/-8.0 days, P=ns). (b) 30-days follow-up: non-fatal myocardial infarction (2.6% vs 4.2%, P=ns), death (2.6% vs 11.1%, P=0.030) and combined outcome (5.3% vs 15.3%, P=0.031). (c) 12 month follow-up: non-fatal myocardial infarction (3. 9% vs 4.2%, P=ns), death (3.9% vs 12.5%, P=0.053), combined outcome (7.9% vs 16.7%, P=ns), re-admissions for unstable angina: (17.1% vs 23.6%, P=ns), late coronary angioplasty: (15.8% vs 11.1%, P=ns) and (d) late coronary bypass grafting: (7.9% vs 12.5%, P=ns).

CONCLUSION

Invasive treatment of patients with refractory angina in remote areas without surgical back-up results in significant in-hospital stabilization and a reduction in major events in-hospital and at 30 days. Coronary angioplasty in stand-alone units and air-transfer of these patients seems safe.

Some observations on the mechanism of pressure related atrial fibrillation

In order to investigate the effect of atrial pressure on the propensity of the atria to fibrillate and the mechanism of this association, the right atrial pressure was changed acutely by transfusion-bleeding in 12 anaesthetized open-chest dogs. Under various atrial pressures the conduction time was measured between two pairs of hook electrodes positioned on the two atrial appendages respectively. The effective refractory period was measured by continuous pacing of the right atrium at a 250 ms cycle length at double threshold intensity and interpolating a progressively earlier stimulus after each eighth paced beat. The propensity of fibrillation was studied by rapid (450 min-1) pacing of the atria at double threshold intensity for 10 s at different atrial pressures. At a high (> or = 14 mmHg) atrial pressure the conduction time (45.7 +/- 14.2 ms) was significantly (P < 0.01) longer, the effective refractory period (157.9 +/- 15.2 ms) significantly (P < 0.01) longer and the atrial fibrillation (11/19 or 57.9%) significantly (chi 2 = 9.95, P < 0.001) more common than at a low (< or = 10 mmHg) pressure (35.2 +/- 11.6, 146.2 +/- 12.4, 3/24 or 12.5%, respectively). Analysis of variance showed that the probability of atrial fibrillation was significantly affected by the atrial pressure but not by either the conduction time or the effective refractory period. The findings suggest that an increase in right atrial pressure by acute volume overload prolongs the inter-atrial conduction time and right atrial refractoriness and increases the propensity of the atria to fibrillate by rapid atrial stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial pressure and experimental atrial fibrillation

A possible profibrillatory effect on the atria of an elevated atrial pressure and the site of atrial stimulation was examined. In 15 anesthetized dogs, right or left atrial or biatrial pacing was applied at a high rate (300-600/min) for 5 seconds at double threshold intensity under a wide range of atrial pressures achieved by venous or arterial transfusion or bleeding. Induction of atrial fibrillation in 236 of 1,971 pacing runs was associated with a significantly higher (P < 0.001) atrial pressure (21.6 +/- 12.2 mmHg, mean +/- SD) than maintenance of sinus rhythm (16.8 +/- 11.1 mmHg in 1,735 of 1,971 pacing runs). Stimulation of the right atrium resulted in atrial fibrillation more frequently than left atrial or biatrial stimulation, with biatrial stimulation less frequent than right or left atrial stimulation. The induction of atrial fibrillation was related to the atrial pressure and to the site of stimulation but not to the pacing rate or the prepacing heart rate. The prepacing heart rate, associated with failure to induce sustained atrial fibrillation, was higher than that associated with atrial fibrillation in 12 of 15 experiments (significantly in 6) and not significantly lower in 3 of 15. Atrial fibrillation lasting 1 minute or more was more frequently associated with simultaneous stimulation of both atria than of either atrium alone. Thus, an elevated atrial pressure may facilitate the induction of atrial fibrillation. The site of stimulation also plays an important role for both the induction and maintenance of atrial fibrillation in this model.

Acute changes in blood pressure as a cause of cardiac arrhythmias

The effect of an acute change in blood pressure (BP) on ventricular ectopic activity and the influence of antiarrhythmic agents on this effect were examined in 24 patients. In 11 patients with premature ventricular complexes (PVCs), the BP was temporarily reduced by a sodium nitroprusside drip. In all of them the incidence of PVCs was reduced (or annihilated) by the induced hypotension. In 13 patients without ventricular ectopic activity, a metaraminol drip was given until either a PVC appeared or the systolic BP reached 200 mmHg, or symptoms appeared. In 12 cases at least one PVC appeared and in 8 of them the total number of PVCs was 13 or more, usually in the form of bigeminy. The repetition of the test following quinidine administration (serum quinidine level 1.7 +/- 0.5 ng ml-1) in 6 cases did not change this pattern, with one exception. It prevented the appearance of idioventricular accelerated rhythm in one case in whom this rhythm had been induced by the hypertension provocative test before the quinidine administration. All cases, in whom the test failed to induce more than 3 PVCs, had no cardiac problem at all. Six of the 8 cases in whom the test induced 13 or more PVCs had organic cardiac disease or palpitation. Other arrhythmias observed on BP elevation, were supraventricular extra beats, nodal escape rhythms and atrioventricular block. In one case with cardiomyopathy, the BP elevation was associated with early signs of heart failure that subsided quickly. In conclusion, acute elevation on BP may be associated with the generation of PVCs and its reduction with their reduction or disappearance.

Idiopathic dilated cardiomyopathy: lack of association with hepatitis C virus infection

OBJECTIVE

To determine whether there is an association between hepatitis C virus (HCV) infection and dilated cardiomyopathy in a well defined area of north western Greece; such an association has been reported elsewhere.

DESIGN

Evaluation of consecutive patients with chronic HCV infection for the presence of clinical or subclinical manifestations of dilated cardiomyopathy by history, physical examination, and non-invasive laboratory procedures (ECG, chest x ray, and echocardiography) before the initiation of interferon alpha treatment; investigation for HCV infection markers in patients with dilated cardiomyopathy by enzyme and immunoblot assays (antibodies to HCV) and the reverse transcriptase polymerase chain reaction (HCV RNA).

SETTING

A tertiary referral centre for patients with chronic hepatitis and dilated cardiomyopathy.

PATIENTS

102 patients with well defined chronic HCV infection and 55 patients with well established dilated cardiomyopathy were evaluated.

MAIN OUTCOME MEASURES

The need for HCV testing in patients with dilated cardiomyopathy, or follow up for heart disease in patients with chronic HCV infection.

RESULTS

None of the patients with chronic HCV infection had clinical or subclinical evidence of dilated cardiomyopathy from history and laboratory findings. None of the patients with dilated cardiomyopathy was positive for antibodies to HCV or viraemic on HCV RNA testing.

CONCLUSIONS

The study neither confirms the findings of other investigators, nor indicates a pathogenic link between HCV and dilated cardiomyopathy. For this reason, at least in Greece, testing for HCV in patients with dilated cardiomyopathy or follow up for heart disease in HCV patients appears unnecessary. Genetic or other factors could be the reason for this discrepancy if previously reported associations between HCV and dilated cardiomyopathy or hypertrophic cardiomyopathy were not coincidental.

Segmental wall motion abnormalities alter vulnerability to ventricular ectopic beats associated with acute increases in aortic pressure in patients with underlying coronary artery disease

OBJECTIVE

To evaluate whether patients with coronary artery disease are susceptible to pressure related ventricular arrhythmias, and if so to identify possible risk factors.

DESIGN

Interventional study.

METHODS

Metaraminol was given to 43 patients undergoing coronary arteriography for ischaemic heart disease to increase their aortic pressure, provided their systolic blood pressure was < 160 mm Hg and they were in sinus rhythm, without any ventricular ectopic activity (or with fewer than six ventricular ectopic beats a minute) during a five minute control period.

RESULTS

During the metaraminol infusion, systolic aortic pressure rose from 131 (15) to 199 (12) mm Hg (mean (SD)). Ventricular ectopy appeared (or ventricular ectopic beats increased by > 100%) in 13/43 patients. Ventricular ectopy was not related to age, sex, presence of hypertension, history of myocardial infarction, use of beta blockers, positive exercise test, number of vessels diseased, or heart rate change during metaraminol infusion. There was a strong relation between the appearance of ventricular arrhythmia and segmental wall motion abnormalities: 1/19 (5.3%, 95% confidence interval 0.1% to 26.0%) without abnormality; 2/12 (16.7%, 2.1% to 48.4%) with hypokinesia; and 10/12 (83.3%, 51.6% to 97.1%) with akinesia or dyskinesia, chi 2 = 22.7, p < 0.001). Ejection fraction was also a significant but not independent risk factor.

CONCLUSIONS

Patients with segmental wall motion abnormalities are predisposed to ventricular ectopic beats during an increase in systolic aortic pressure. This could be explained by associated electrophysiological inhomogeneity. The presence of mechanical inhomogeneity, as may occur in postinfarction akinesia or dyskinesia, may affect the aortic pressure above which ventricular arrhythmias appear.

Clinical characteristics and follow-up of patients with chest pain and normal coronary arteries

The authors identified 160 men and women from all 3,700 patients with anginal pain between 1990 and 1994 who were subsequently found to have normal coronary arteries at diagnostic cardiac catheterization with follow-up to the present (mean follow-up 2.5 years). The group comprised 50 women and 110 men. Mean age was significantly greater in women (53.1 +/- 7.7 vs 47.2 +/- 9.2 years, p<0.001). Forty percent of the women but only 10% of the men had a positive exercise test. At follow-up, a larger proportion of patients continue to experience chest pain (95 patients, 59%) of whom 65 patients (41%) continue antianginal therapy. Furthermore one patient suffered a sudden cardiac death and two patients had a nonfatal myocardial infarction. Of patients referred with chest pain, women were more likely to have normal coronary arteries, compared with men. All patients have an excellent prognosis. A large proportion of women had a positive exercise test in the absence of coronary artery disease. On the other hand, morbidity remains high in these patients, despite the reassurance of a normal-appearing coronary arteriogram.

High blood pressure and ventricular arrhythmias

Here we review the blood pressure-ventricular arrhythmia relationship. An increase in blood pressure, by any means, may induce ventricular arrhythmias both experimentally and in patients with a history of ventricular ectopic beats. Conversely, a decrease in blood pressure may eliminate ventricular arrhythmias due to other causes. The increased pressure is sensed in the ventricles. Both systolic and diastolic loading may induce important electrophysiological changes. However, an increase in systolic pressure may induce ventricular ectopy even though the left atrial pressure remains low; on the other hand, raising the atrial pressure does not induce ectopic rhythms unless associated with an increase in arterial pressure. This phenomenon (mechanoelectrical association or contraction-excitation feedback) seems to be a direct one not mediated by either ischaemia or adrenergic stimulation. Both refractoriness and intraventricular conduction are affected by mechanical loading, although the direction of change depends on several factors. The mechanism of pressure-related arrhythmias remains obscure. Triggered activity due to early after-depolarizations is one possibility. Ventricular arrhythmias observed in chronic hypertension might be a clinical manifestation of mechano-electrical association, especially when they occur in conjunction with acute blood pressure elevations. Several antihypertensive agents with different mechanisms of action also have an antiarrhythmic effect. Extensive research to establish the antiarrhythmic effectiveness of antihypertensive treatment in cases with ventricular arrhythmias is still warranted.

Arrhythmogenic effect of high blood pressure: some observations on its mechanism

An increase in aortic pressure is a reproducible way of causing ventricular ectopic rhythms. This study sought to determine whether it is the aortic pressure per se or the concommitant increase in afterload or preload that has a direct arrhythmogenic effect. Experiments were carried out in 17 anaesthetised dogs. For each 10 s period the pressure and the presence of a ventricular arrhythmia (at least one ectopic beat) were noted. In nine animals an aortic valve gradient was created (and released). The results were compared to those obtained by impeding the aortic flow at the ascending aorta. The mean systolic left ventricular pressure was significantly higher in the arrhythmia associated periods in 8/9 experiments when there was an aortic valve gradient and in 5/9 experiments when there was not. In 4/9 experiments the mean aortic pressure associated with arrhythmia was significantly lower with an aortic valve gradient than when there was no gradient and no arrhythmia. In 7/9 of these experiments, coronary sinus flow was measured volumetrically during the manoeuvres applied. The coronary flow was significantly lower when there was neither arrhythmia nor aortic valve gradient than when there was an arrhythmia (with or without an aortic valve gradient). In another eight experiments a pressure reservoir in the aorta was either raised or lowered while another pressure reservoir in the left atrium was moved in the opposite direction. Thus the mean aortic pressure could be increased while the left atrial pressure was decreased and vice versa. If the left atrial pressure was taken into account, the mean difference of the aortic pressure from its expected value, derived from the aortic v left atrial pressure regression equation, was significantly higher when there was an arrhythmia than it was when there was no arrhythmia in all eight experiments. On the other hand, the mean difference in the left atrial pressure from its expected value was significantly higher when there was an arrhythmia in 1/8, lower in 2/8 and not significantly different in 5/8 experiments. It is concluded that when the blood pressure is raised, it is the increase in afterload rather than an increase in aortic pressure itself or in the preload that has an arrhythmogenic effect on the ventricles.

For debate . . . Individual contributions to multiauthor papers

The curricula vitae of four candidates for a professorial appointment at Athens University were examined to estimate the actual contribution of each candidate to the papers of which he was a coauthor. A total of 879 research papers by the four candidates were analysed in terms of the number of authors, the sequence of names, and the year of publication. The four authors presented 364, 349, 96, and 70 papers. If an equal contribution of all coauthors is assumed, the actual number of papers (all papers divided by the number of authors), is about 106, 83, 28, and 26, respectively, so that the rank of the four candidates did not change. On the assumption that the contribution was related to the candidate's position in the order of the coauthors' names, the numbers of papers were corrected to 84, 95, 26, 33 using one statistical method and to 88, 94, 28, 31 using another. These assumptions may not be valid, however, especially as the last author may be more important than the intermediate ones. It is suggested that the journals require authors to state their specific contribution to a paper, such as original idea, planning, collecting data, writing up, etc.

Platelet aggregatory response to platelet activating factor (PAF), ex vivo, and PAF-acetylhydrolase activity in patients with unstable angina: effect of c7E3 Fab (abciximab) therapy

OBJECTIVE

Platelet activation and aggregation is a dominant feature in the pathophysiology of unstable angina. The final step of platelet aggregation is mediated through the platelet integrin glycoprotein IIb/IIIa (GP IIb/IIIa), while abciximab (ReoPro) is one of the most potent inhibitors of this receptor. Platelet-activating factor (PAF) is a potent platelet agonist which is degraded and inactivated by PAF-acetylhydrolase (PAF-AH). The plasma form of PAF-AH is associated with lipoproteins. We studied the platelet response to the aggregatory effect of PAF, ex vivo, in relation to the plasma PAF-AH activity in 32 patients with unstable angina, as well as the effect of abciximab therapy on the above parameters.

METHODS

Thirty two patients with unstable angina and 25 sex- and age-matched healthy controls participated in the study. On the day of admission (day 1) 17 patients received a bolus of abciximab (0.25 mg/kg) followed by a 12-h infusion (10 micrograms/min). Platelet aggregation to both PAF and ADP, in platelet rich plasma, was successively studied in both patients receiving abciximab or remaining untreated. The plasma and HDL-associated PAF-AH activity was also determined at the same times.

RESULTS

In the untreated patients, the PAF EC50 values were significantly lower on the day of admission, whereas the maximal percentage of aggregation was significantly higher compared to controls (p < 0.01 for both comparisons). Similar behaviour of the platelets was observed in the aggregatory effect of ADP. This aggregatory response was not significantly altered 4 days, 7 days or 1 month afterwards. In the 17 patients who received abciximab, platelet aggregation to both PAF and ADP was inhibited by 90 +/- 5 and 96 +/- 3%, respectively, 1 h after bolus. At 2 and 3 days after treatment, platelet aggregation to both agonists was significantly recovered being similar to controls. However, it was fully restored 6 days after bolus, still being significantly higher compared to controls (p < 0.01 for PAF and p < 0.003 for ADP). The total plasma PAF-AH activity in both patient groups was not different from that of controls, whereas the HDL-associated PAF-AH activity was significantly lower. The total plasma or HDL-associated enzyme activity was not altered at any time interval studied, and it was not influenced by abciximab.

CONCLUSIONS

The increased aggregatory response of platelets to PAF and the low plasma levels of HDL-cholesterol and HDL-associated PAF-AH activity in patients with unstable angina may contribute to the severe atherosclerosis and to acute thrombosis found in these patients. Abciximab therapy may protect platelets from PAF action in vivo the first days after drug administration, but it fails to permanently restore the enhanced aggregatory response observed.

Use of vibrational angioplasty for the treatment of chronic total coronary occlusions: preliminary results

The aim of the study was to investigate the feasibility and clinical safety of vibrational angioplasty in the treatment of chronic total coronary occlusions and evaluate the clinical and angiographic factors that are predictive of the procedural success and complications of the procedure. Seventy-eight patients with chronic total occlusions (>3 months) resistant to conventional techniques were treated by vibrational angioplasty using a variety of conventional guidewires. Lesions were successfully crossed in 67 (85.9%) cases and antegrade flow was achieved in 59 (75.5%). Major complications (myocardial infarction and tamponade) occurred in two (2.5%) patients, but no fatalities ensued. Angiographically detectable dissections were seen in 23 (29.5%) patients but only resulted in vessel compromise and reclosure in 5 cases. Multiple stepwise logistic regression analysis identified the duration (<6 months, P = 0.008) and the length of the occlusion (<15 mm, P = 0.03) as independent predictors of final success and the age of the patient (<55 years, P = 0.006) as the only independent predictor of procedural complications. Vibrational angioplasty is a safe technique useful in the treatment of chronic coronary occlusive disease. Patients in whom the procedure is likely to prove most successful may be easily identified by clinical and angiographic features (duration and length of occlusion).

Direct current shock and digitalis. A clinical and experimental study

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Effect of acute hypertension on the cardiac rhythm. Experimental observations

An acute increase in blood pressure (BP) may be associated with the genesis of ventricular ectopy. Fourteen anesthetized dogs were examined to find out whether the critical pressure that causes an arrhythmia may be an index of the tendency of the myocardium to generate ectopic rhythms. An acute change in BP was produced 321 times using an arterial pressure reservoir or aortic obstruction or a metaraminol infusion or, inversely, arterial bleeding. Each time the BP was increased, cardiac arrhythmias appeared and each time the BP was decreased the cardiac arrhythmias disappeared. The most common type of arrhythmia was ventricular ectopy (123/167 acute BP increases), usually in a form of bigeminy. The next most common rhythm disturbance was atrioventricular block (32/167 acute BP increases), especially when a constant rate was achieved by atrial pacing. The BP above which an arrhythmia appeared varied greatly among different animals (189.0 +/- 55.1 mmHg, means +/- SD). It was significantly (p less than 0.01) reduced (-29.0 +/- 17.1 mmHg) following coronary ligation and significantly (p less than 0.05) raised (+/- 41.6 +/- 38.7 mmHg) following lidocaine administration. The incidence of ventricular ectopy on increasing the BP was significantly higher at low heart rates in ten experiments, lower in two and not significantly different in 14. The incidence of premature ventricular complexes, the degree of atrioventricular block and the PR interval in first-degree atrioventricular block, whenever these rhythm disorders appeared, were a function of the BP level. It is concluded that an acute increase in BP may cause rhythm disturbances, usually in the form of ventricular ectopy and/or atrioventricular block.(ABSTRACT TRUNCATED AT 250 WORDS)

Susceptibility of the right and left canine atria to fibrillation in hyperglycemia and hypoglycemia

The objective of this study was to investigate the changes in the refractory period and in the susceptibility to fibrillation of canine atria associated with different levels of glycemia, and the differences in these parameters between the two atria. In 20 anesthetized, open-chest dogs weighing 24 kg, the effective refractory period was measured by atrial pacing with a run of 8 stimuli (S1-S1 350 ms) followed by a progressively earlier S2 until no stimulation of the atrial tissue occurred. The susceptibility to fibrillation was assessed by applying DC at 2, 3, and 4 V for 3 seconds, 7 times each, on the atrial appendage. If fibrillation occurred and persisted for 3 minutes, a transthoracic synchronized shock was delivered (200 J). The refractory period and the susceptibility to fibrillation were assessed under normoglycemia first, and then under hypo and hyperglycemia, in the right and left atrium successively, in random order. The incidence of induced atrial fibrillation in the right atrium was: hypoglycemia 31.96% (132 of 413 attempts); normoglycemia 24.11% (81 of 336; p < 0.05); and hyperglycemia 20.23% (85 of 420). Results for the left atrium were hypoglycemia 52.06% (215 of 413); normoglycemia 40.18% (135 of 336; p < 0.005); and hyperglycemia 32.86% (138 of 420; p < 0.05). Sustained atrial fibrillation (> 3 minutes) occurred significantly more often under hypo rather than hyperglycemia and stimulated the left rather than the right atrium. The refractory period was shortest under hypoglycemia in the left atrium and longest under normo or hyperglycemia in the right atrium.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct current shock and antidysrhythmic drugs

A review is given of 457 episodes of atrial fibrillation that occurred in 318 patients and were treated by DC shock. Antidysrhythmic drugs, such as quinidine, procainamide, and propranolol, given singly or in combination, were used concomitantly in 389 instances, and DC shock alone was given in 68 instances. The combined effects of quinidine and DC shock, and of procainamide and DC shock were studied in the experimental animal.Combined DC shock and drug therapy gave a higher conversion rate than DC shock alone, and a statistically significant difference was found in respect of the group of patients receiving procainamide and propranolol together (p<0.01). Antidysrhythmic drugs failed on the whole to reduce the incidence of DC shock-induced dysrhythmias. However, the incidence of certain digitalis and DC shock-induced dysrhythmias was significantly less when propranolol and procainamide were given as pretreatment than when procainamide or quinidine was given alone (p<0.01). In animal experiments, quinidine had no protective action against digitalis and DC shock-induced ectopic tachycardias. Clinical and experimental observations suggest that the cardiotoxicity of these drugs may be enhanced by DC shock. Immediate or delayed post-shock rhythm disorders can be drug related and, therefore, great caution should be exercised in the use of antidysrhythmic drugs in conjunction with DC shock therapy.

Cardiac involvement in collagen diseases

The purpose of this study is to evaluate the early morphological and functional abnormalities of the heart in patients with collagen disease. The study population was free of risk factors for coronary artery disease and without any clinically evident cardiac manifestations. In 62 patients with collagen disease (25 with progressive systemic sclerosis, 19 with systemic lupus erythematosus, 15 with rheumatoid arthritis, three with dermatomyositis) and in 40 healthy subjects an echocardiographic study was performed. Echocardiographic examination from the apical four-chamber view was performed at rest and during the end of a 3 min isometric exercise with handgrip. Global and regional ejection fraction of the left ventricle were calculated. In the group with progressive systemic sclerosis the left ventricular mass index was significantly higher than in the control group (110.78 +/- 48.61 vs 82.18 +/- 28.46 g.m-2) and the ejection fraction (53.61 +/- 7.95%) was the lowest of all groups (control: 61.47 +/- 8.52%, systemic lupus erythematosus: 59.04 +/- 8.58%, rheumatoid arthritis: 62.38 +/- 6.88%). Regional ejection fraction analysis revealed a major dysfunction of the proximal segment of the interventricular septum, in all groups. During isometric exercise, the global and regional ejection fraction did not change significantly, although differences between groups disappeared. In rheumatoid arthritis, mitral and aortic valve leaflet separation appeared to be reduced. In the group with systemic lupus erythematosus, mild abnormalities were noticed, although the mean age and duration of the disease were the smallest compared with the other groups. In conclusion, patients with progressive systemic sclerosis mainly present left ventricular hypertrophy with a reduced ejection fraction while rheumatoid arthritis patients show a predominant valve dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

An epidemiological study of symptomatic paroxysmal atrial fibrillation in northwest Greece

AIM

Although atrial fibrillation (AF) is the most commonly sustained arrhythmia, information about its incidence in the general population is sparse. Even more sparse is information on an important variety of AF, paroxysmal AF. The aim of this study is to assess the frequency of new cases of symptomatic paroxysmal AF per year ('incidence') in a general unselected population and to compare other epidemiological features with chronic AF patients.

METHODS AND RESULTS

Over a 4 year period, we conducted a prospective, population-based survey of cases of AF in a defined geographical area with a known population size stratified for age and sex. Sources of identification were the two hospitals which serve the area and all the primary care settings. Patients with AF of less than 7 days duration were characterized as paroxysmal AF and all others as chronic AF. During the study period we identified 1551 patients with chronic AF (51.7% male, mean age 71 +/- 10.4 years and 48.3% females, mean age 73.1 +/- 10.8 years) and 443 patients with paroxysmal AF (59.6% male, mean age 59.6 +/- 13.3 years and 40.4% female, mean age 65.2 +/- 10.1 years). There was no underlying cardiovascular disease in 15.6% and 32.3% of patients with chronic and paroxysmal AF, respectively. The mean annual occurrence of new cases of paroxysmal AF was 6.2/10,000/year, and was higher (P<0.01) for men (7.2/10,000/year) than for women (5.3/10,000/year). The frequency of new paroxysmal AF cases rises with age, reaching a peak at 70-79 years and then declines.

CONCLUSIONS

We conclude that paroxysmal AF is a relatively common arrhythmia, the occurrence of which increases with age and is more frequent in younger men than in women. Patients with chronic AF are older and more often have underlying heart and other disease than patients with paroxysmal AF.

Platelet aggregability to platelet activating factor at rest and after exercise in patients with coronary artery disease

The platelet response to the aggregatory effect of platelet-activating factor (PAF) in relation to blood PAF levels, serum PAF-acetylhydrolase (PAF-AH) activity and to their lipidaemic profile, was studied in 44 patients with coronary artery disease undergoing exercise tests. The PAF EC50 values in 21 patients with positive exercise test results were found to be significantly decreased at rest compared with 21 normal subjects (12.6 +/- 3.9 nM and 24.9 +/- 11.7 nM respectively) (P<0.0001). Moreover, the maximal percentage of aggregation to 50 nM PAF was found to be significantly increased (20.0 +/- 4.3% vs 13.5 +/- 3.6%, respectively) (P<0.0001). By contrast, the PAF EC50 values and the maximal percentage of aggregation in 23 patients with negative exercise test results were not statistically significantly different from the control group (25.2 +/- 11.4 nM and 14.1 +/- 4.7%, respectively). At the end of exercise, the PAF EC50 values and the maximal percentage of aggregation did not change in any group, and there were no significant differences in the whole-blood PAF levels either at rest or at the end of exercise. In patients with positive exercise test results, the PAF-AH activity at rest was significantly higher compared with the control group (37.2 +/- 8.0 nmol.ml(-1).min(-1) vs 32.4 nmol.ml(-1).min(-1), (P<0.03), whereas the enzyme activity did not differ in patients with negative exercise test results compared to controls (33.6 +/- 6.1 nmol.ml(-1).min(-1)). There was no change in PAF-AH activity during exercise in any group. The enzyme activity was positively correlated to the serum total and low density lipoprotein (LDL) cholesterol levels in the control group and in patients with negative exercise test results, whereas no correlation was found between PAF-AH activity and total or LDL cholesterol levels in patients with positive exercise test results.