Additively manufactured Ti-6Al-4V thin struts via laser powder bed fusion: Effect of building orientation on geometrical accuracy and mechanical properties.

Porous metal lattice structures have a very high potential in biomedical applications, setting as innovative new generation prosthetic devices. Laser powder bed fusion (L-PBF) is one of the most widely used additive manufacturing (AM) techniques involved in the production of Ti6Al4V lattice structures. The mechanical and failure behavior of lattice structures is strongly affected by geometrical imperfections and defects occurring during L-PBF process. Due to the influence of multiple process parameters and to their combined effect, the mechanical properties of these structures are not yet properly understood. Despite the major commitment to characterize and better comprehend lattice structures, little attention has been paid to the impact that single struts have on the overall lattice properties. In this work, the authors have investigated the tensile strength and fatigue behavior of thin L-PBF Ti6Al4V lattice struts at different building orientations (0°, 15°, 45°, and 90°). This investigation has been focused on the effect that microstructural defects (particularly porosity) and actual surface geometry (including surface texture and geometrical errors such as varying cross-section shape and size) have on the mechanical performances of the struts in relation to their building direction. The results have shown that there is a tendency, particularly for low printing angles, of fatigue life to decrease with decreasing of the building angle. This is mainly due to the surge in surface texture and loss in cross-sectional regularity. On the other hand, the monotonic tensile test results have shown a low sensitivity to these factors. The strut failure behavior has been examined employing dynamic digital image correlation (DIC) of tensile tests and scanning electron imaging (SEM) of the fracture surfaces.

Fatigue and biological properties of Ti-6Al-4V ELI cellular structures with variously arranged cubic cells made by selective laser melting.

Traditional implants made of bulk titanium are much stiffer than human bone and this mismatch can induce stress shielding. Although more complex to produce and with less predictable properties compared to bulk implants, implants with a highly porous structure can be produced to match the bone stiffness and at the same time favor bone ingrowth and regeneration. This paper presents the results of the mechanical and dimensional characterization of different regular cubic open-cell cellular structures produced by Selective Laser Melting (SLM) of Ti6Al4V alloy, all with the same nominal elastic modulus of 3GPa that matches that of human trabecular bone. The main objective of this research was to determine which structure has the best fatigue resistance through fully reversed fatigue tests on cellular specimens. The quality of the manufacturing process and the discrepancy between the actual measured cell parameters and the nominal CAD values were assessed through an extensive metrological analysis. The results of the metrological assessment allowed us to discuss the effect of manufacturing defects (porosity, surface roughness and geometrical inaccuracies) on the mechanical properties. Half of the specimens was subjected to a stress relief thermal treatment while the other half to Hot Isostatic Pressing (HIP), and we compared the effect of the treatments on porosity and on the mechanical properties. Fatigue strength seems to be highly dependent on the surface irregularities and notches introduced during the manufacturing process. In fully reversed fatigue tests, the high performances of stretching dominated structures compared to bending dominated structures are not found. In fact, with thicker struts, such structures proved to be more resistant, even if bending actions were present.

Atrial fibrillation in elite athletes.

INTRODUCTION: Atrial fibrillation (AF) is a rare event in people younger than 25 years of age, but is probably more frequent in competitive athletes. We analyzed the presence of AF, paroxysmal or chronic, in a population of young elite athletes, including previous Olympic and World champions, who were studied for arrhythmias that endangered their athletic careers. METHODS AND RESULTS: From 1974 to June 1977, 1,772 athletes identified with arrhythmias (1,464 males and 308 females; mean age 21 years) underwent individualized work-ups. Among these, 146 (122 males and 24 females; mean age 24 years) were young elite athletes. They were studied from 1985 to 1997, with a mean follow-up of 62 months. Of the 146 young elite athletes, 13 (9%) had AF (paroxysmal in 11 and chronic in 2); all were male. The paroxysmal AF occurred during effort (n = 7), after effort (n = 1), or at rest (n = 3) and was reinduced by transesophageal pacing or endocavitary electrophysiologic testing under the same clinical circumstances. AF was the cause of symptoms in 13 (40%) of 22 young elite athletes with long-lasting palpitations. Five young elite athletes had a substrate for AF: Wolff-Parkinson-White syndrome (WPW) in 3, arrhythmogenic right ventricular dysplasia (ARVD) in 1, healed myocarditis in 1, and was considered idiopathic in 8. All elite athletes are alive with a mean follow-up of 62 months and 7 continue in their sports: 3 after radiofrequency catheter ablation (of WPW in 2 and AF with maze-type nonfluoroscopic approach in 1) and 4 after a period of de-training. CONCLUSIONS: AF, occurring in young elite athletes and affecting only males, is one of the most frequent causes of prolonged palpitations and is reproduced easily by transesophageal atrial pacing or electrophysiologic testing. AF may be a cause of disqualification from sports eligibility, but may disappear if the athletic activity is stopped for an adequate period of time, if trigger mechanisms are corrected (i.e., WPW), or if the substrate is modified.

Cardiac arrest and sudden death in competitive athletes with arrhythmogenic right ventricular dysplasia.

Arrhythmogenic right ventricular dysplasia (ARVD) is a predisposing factor for sport-related cardiac arrest (CA), sudden cardiac death (SD), and life-threatening ventricular tachyarrhythmias (VT). The aim of this study was the assessment of athletes with ARVD, particularly the CA survivors. From 1974 to January 1996, 1642 competitive athletes (aver. 25.5 yr.), 136 of whom were top level athletes (TLA), were studied for important arrhythmic manifestations. All athletes underwent an individualised study protocol including a series of non invasive and invasive diagnostic techniques. One hundred and one athletes (90 males, 11 females, aver. 25.9 yr.) were diagnosed as being affected by ARVD on the basis of the WHO/ISFC criteria. The same percentage (about 6%) of ARVD is present in both the general arrhythmic athletes population and in the subgroup of TLA. Prevalence of ARVD among athletes with CA or SD is high (respectively 23% and 25%), confirming the observation that ARVD is one of the major causes of SD in Italian athletes. All CA were athletic activity related, indicating the potentiality of exercise as a cause of electrical destabilisation in subjects with ARVD. In athletes with documented ARVD intense sport activity has to be proscribed. In athletes at risk of CA or SD an aggressive treatment, ICD implantation and RF catheter ablation must be taken into consideration.

Life-threatening tachyarrhythmias in athletes.

The arrhythmias in competitive athletes may be classified as "benign," "paraphysiological" due to prolonged athletic training, or "pathological" due to hemodynamic effects on the athletic performance-risk-arrhythmogenic substratum. Pathological arrhythmias include life-threatening forms that are severe enough to produce symptoms (presyncope, syncope, cardiac arrest) during athletic activity. These forms are in particular rapid VT, VF, torsades de pointes, preexcited atrial fibrillation, sinus atrial and AV block. Our study population includes 766 competitive athletes, mean age 21.1 years (74 top international level), investigated with a cardioarrhythmological work-up for symptoms and for arrhythmias from 1974 to June 30, 1991. Three leading categories, represented by 16 aborted sudden death, 8 sudden death, and 7 induced VF (by EES or TAP) athletes, are described. All athletes with life-threatening arrhythmias, previously as asymptomatic or with minor symptoms had an arrhythmogenic substratum due to underlying silent cardiopathy or primary arrhythmic disorders. Athletic activity can be regarded as a trigger of electrical destabilization.

Long-term follow-up of patients with inducible supraventricular tachycardia treated with flecainide or propafenone: therapy guided by transesophageal electropharmacologic testing.

We report our experience with flecainide and propafenone therapy for inducible supraventricular tachycardias and paroxysmal supraventricular tachycardias due to atrioventricular (AV) nodal reentry or the Wolff-Parkinson-White syndrome. We performed an electropharmacologic test (ET) that consisted of first inducing a clinical arrhythmia by transesophageal atrial pacing (TAP) protocol. This was followed by intravenous drug administration and TAP reevaluation, either after acute intravenous administration or in oral steady-state. We used ET with flecainide and/or propafenone to study 2 groups of patients at least 3 years before the long-term clinical observation period. The first group was comprised of 58 patients with reciprocating tachycardias--due to AV node reentry in 17 (29.3%) and anomalous pathway in 41 (70.7%). Twelve (29.3%) of the latter had reciprocating tachycardias, 15 (36.6%) had atrial fibrillation, and 14 (34.2%) had both arrhythmias. During ET, flecainide was administered to 42 patients, and the ET was considered positive in 28 (66.7%). Propafenone was administered to 32 patients, with positive results in 15 (46.9%). In 15 patients, both flecainide and propafenone were tested, 8 receiving flecainide after a negative ET with propafenone, and 7 receiving propafenone after a negative ET with flecainide. In the first group, the ET was positive in 7 (87.5%), and in the second group, it was positive in 3 (42.9%). In a follow-up of 40.1 +/- 11 months, 38 (65.5%) patients had positive outcomes, 5 (8.6%) had to stop receiving the drugs because of side effects, 3 (5.2%) stopped because of inefficacy, and 12 (20.7%) dropped out.(ABSTRACT TRUNCATED AT 250 WORDS)

Electropharmacological testing by transoesophageal atrial pacing in inducible supraventricular tachyarrhythmias. A good approach for selection of long-term anti-arrhythmic therapy.

Sixty-eight patients with disabling episodes of inducible supraventricular tachyarrhythmia were tested electropharmacologically by transoesophageal atrial pacing. Using this technique we induced clinical arrhythmia in 67 (98.5%); 26 (38.8%) had a reciprocating tachycardia due to AV node reentry and 41 (61.2%) a by-pass tract. In the latter we induced a reciprocating tachycardia in 12 (29.3%), atrial fibrillation in 25 (36.5%) and both in 14 (34.2%). We then performed an anti-arrhythmic drug test and a transoesophageal reevaluation either after acute intravenous drug administration or during oral steady state. Altogether we tested 111 drugs or a combination of drugs before the results were considered positive; all patients tolerated the procedure well and were discharged with the drug or combination of drugs judged effective. At follow-up of 16.6 +/- 8.5 months, 42 patients (62.7%) were symptom-free, 17 (25.3%) had minor and non-disabling relapses, six (9%) stopped the drug because of inefficacy (1-1.5%) or side effects (5-7.5%); two (3%) dropped out. We conclude that electropharmacological testing with transoesophageal pacing constitutes a very good approach for inducible supraventricular tachyarrhythmias: it permits selection of optimal long-term anti-arrhythmic treatment and is well tolerated, only slightly invasive and without adverse effects.

[Supraventricular reentry tachycardia and athletic fitness]. / Tachicardia da rientro sopraventricolare ed idoneità sportiva.

Paroxysmal supraventricular reciprocating tachycardias (PSRT) which are due to a different type of reentry including the atrioventricular reentry circuit of Wolff-Parkinson-White (WPW) syndrome, may disturb the professional career of an athlete. Moreover even severe episodes of preexcited atrial fibrillation of WPW may occur. PSRT in athletes may present various clinical consequences: unimportant symptoms, or severe hemodynamic effects on the athletic performance particularly during sports activity at intrinsic high risk. The athletes are evaluated by clinical protocol which includes Holter monitoring ergometric test, echocardiography study, thyroid check and transesophageal electrophysiologic study at rest and during exercise. The arrhythmological study should be carefully performed in order to exclude an underlying heart disease, to study electrophysiological mechanisms and possible hemodynamic effect sports activity relate of the inducible and clinical tachyarrhythmias. Sometimes, these PSRT may disappear after interruption of athletic activity because of modifications of electrophysiological conditions related to the sports activity.

[Cardiac rhythm in athletes: a Holter study of top level and ex-professional football players]. / Ritmo cardiaco nell'atleta: studio con Holter in calciatori "top level" ed ex calciatori professionisti.

The study we performed aimed at identifying the arrhythmological pattern in the football player. Between 1984 and 1989, 50 top level football players (group A) from the National Olympic team and from the National A team, average age 24.2 years (min. 19, max. 32), underwent Holter monitoring. The recordings were carried out in different environmental conditions according tot he programmes of the team and the number of recordings depended on how long each football player stayed in the National team. Moreover, 40 trainers (group B) from the Italian football teams, average age 38.4 years (min. 32, max. 57), all of whom had formerly been professional high-level football players practising intensive physical exercise for professional reasons, underwent one 24 h Holter monitoring. RESULTS. Group A: 2621 hours of monitoring were able to be analysed in 48/50 football players. Sinus node pauses greater than or equal to 1750 ms were found in 21/48 (43.7%) with a maximum of 3740 ms on altitude in 1/21, second degree atrioventricular block in 8/48 (16.7%) with a maximum of 5400 ms on altitude in 1/8, supraventricular ectopic beats in 13/48 (27%), ventricular ectopic beats in 26/48 (54.1%) which were complex (cl. Lown greater than or equal to 3) in 7/26. Group B: 882.30 hours of monitoring were able to be analysed in 39/40 former football players. Sinus node pauses greater than or equal to 1750 ms were found in 18/39 (46.1%) with a maximum of 2280 ms in 7/18, second degree atrioventricular block in 1/39 (2.6%) with a maximum of 2400 ms, supraventricular ectopic beats in 32/39 (82%), ventricular ectopic beats in 24/39 (61.5%) which were complex in 5/24.(ABSTRACT TRUNCATED AT 250 WORDS)