Intermediate-term results of Phase I Food and Drug Administration Trials of buttoned device occlusion of secundum atrial septal defects

Outcomes of Device Closure of Atrial Septal Defects

Several devices have been designed and tried over the years to percutaneously close atrial septal defects (ASDs). Most of the devices were first experimented in animal models with subsequent clinical testing in human subjects. Some devices were discontinued or withdrawn from further clinical use for varied reasons and other devices received Food and Drug Administration (FDA) approval with consequent continued usage. The outcomes of both discontinued and currently used devices was presented in some detail. The results of device implantation are generally good when appropriate care and precautions are undertaken. At this time, Amplatzer Septal Occluder is most frequently utilized device for occlusion of secundum ASD around the world.

The Journey of an Indian Pediatric Cardiologist : Dr. K. C. Chaudhuri Lifetime Achievement Award/Oration at AIIMS, New Delhi, September 2017

The life journey of an Indian pediatric cardiologist, who bestowed considerable attention to the development of new knowledge and train/teach physicians around the world while providing care of patients with heart disease over a 45-y period, is reviewed. This appraisal focuses particular attention on the scientific contributions to the literature. These include spontaneous closure of physiologically advantageous ventricular septal defects, various issues related to a congenital heart defect namely, tricuspid atresia and transcatheter and, interventional pediatric cardiac procedures.

Late migration of a Sideris septal occluder device for closure of atrial septal defect into the left atrium with mitral valve obstruction

The transcatheter closure of atrial septal defects provides an alternative to surgery, and various devices, such as the Sideris buttoned device, have been prescribed. Late complications have been rare and have not yet been reported within 2 years of implantation. This report presents a case of delayed migration of a Sideris buttoned device occurring 6 years after successful implantation. In conclusion, this report provides a reminder of the need for careful long-term follow-up of patients receiving transcatheter closure of atrial septal defects, particularly in cases involving the implantation of early-generated devices.

The anaesthetist and the cardiac catheterisation laboratory

Interventional cardiology is an innovative and expanding field. Anaesthetists are increasingly involved in managing complex congenital and acquired heart lesions in the cardiac catheterisation laboratory. This article provides an overview of common lesions encountered in the cardiac catheterisation laboratory, the anaesthetic management of patients with congenital and acquired heart lesions, the procedures performed and the complications encountered during such procedures.

Five-year clinical and echocardiographic evaluation of the Das AngelWings atrial septal occluder

BACKGROUND

The late outcome of patients treated with atrial septal occluder devices remains incompletely defined. The purpose of this study was to assess the late outcome (range 4-7 years postprocedure) of patients in whom the Das AngelWings septal occluder device was implanted in the atrial septum. We report the clinical and echocardiographic outcome, at an average of 5 years following the procedure, of patients treated with the Das AngelWings device used to close either a secundum atrial septal defect (ASD) or a patent foramen ovale (PFO).

METHODS

Thirty-two patients underwent successful percutaneous closure of an atrial septal closure, patent foramen ovale, or fenestration in the lateral tunnel of their Fontan with the Das AngelWings device between June 1995 and March 1998 at Duke University Medical Center. Two of the 32 patients were lost to follow-up. The remaining 30 patients were divided into 3 groups based on indication for device implantation. Group 1 consisted of 14 patients with a secundum ASD and predominantly left-to-right atrial shunting. Group 2 consisted of 8 patients who had a PFO and who suffered a thromboembolic event. Group 3 (compassionate use) consisted of 10 patients with multiple comorbid medical problems with predominantly right-to-left shunting at the atrial level causing hypoxemia. Eight of the patients in group 3 were severely ill at the time of device implantation. The 2 remaining patients in group 3 underwent AngelWings implantation for closure of right-to-left shunting through a Fontan fenestration. Mean follow-up was 59 months.

RESULTS

There was no device embolization. No patient in the ASD or PFO/stroke group had a clinical complication. By radiographic examination, 2 of 27 patients had evidence of fracture of the nitinol framework at 2-year follow-up. Residual shunting was present in 44% at 24 hours, 20% at 1 year, and 18.8% at 2 years by use of Doppler color flow imaging and/or microcavitation echocardiographic studies. Mild mitral regurgitation caused by the AngelWings device occurred in 1 patient. One patient in the compassionate use group had a subsequent neurologic event. Five of the 10 patients in the compassionate use group died of comorbid illnesses in follow-up, none directly related to device complications.

CONCLUSION

The late clinical outcome of secundum ASD and PFO/stroke patients in this study demonstrates that Das AngelWings closure of the atrial septum is effective and safe. These data are encouraging with respect to the expanding use of other percutaneously implanted ASD occlusion devices, although late clinical safety and efficacy data are needed for the specific devices being implanted.

Transcatheter closure of atrial septal defects with the Amplatzer septal occluder--a Japanese clinical trial

This study reports the results of a Japanese clinical trial of transcatheter closure of atrial septal defects (ASD) using the Amplatzer septal occluder (ASO). Thirty-five patients with secundum ASD underwent transcatheter closure using the ASO at a median age of 12.9 years (range, 3.2-29.2 years) and a median weight of 39.2kg (range, 11.6-65.1 kg). The ASO was successfully implanted in 34 patients. The mean ASD diameter of the 34 patients measured by transesophageal echocardiography was 11.7 +/- 4.2mm (range, 5.0-20.8mm) and the mean balloon stretched diameter was 16.8 +/- 4.2 mm (range, 9-25 mm). The mean ASO size was 16.9 +/- 4.3 mm (range, 9-26mm). Complete closure rate at 1 day and 1 year after closure was 91% and 97%, respectively. One patient developed a transient second-degree atrioventricular block during the implantation procedure. No other complications occurred. Transcatheter closure of ASD using the ASO is effective and safe.

Non-surgical closure of atrial septal defect

BACKGROUND

Recently many devices for the transcatheter closure of atrial septal defect (ASD) were developed in the world. Several ASD closing devices, such as Clamshell device, buttoned device, ASD occluder system (ASDOS), Angel Wings, are not fully acceptable from a practical point of view. We reported the clinical trials of transcatheter closure of ASD for Clamshell double umbrella device and Amplatzer septal occluder (ASO) in Japan.

METHODS

Clamshell devices were implanted in 11 patients. Clinical trials for ASO device were carried out in 34 patients in Japan. We reported the results of 17 patients in National Children's Hospital.

RESULTS

Clamshell devices were implanted in all of the patients successfully. Minimal residual shunt was present in four patients (36%), 1 year after the procedure by Doppler color flow imaging. Nine of 11 umbrellas demonstrated fracture of the stainless steel arm. Arm fracture occurred between 1 week and 12 months after implantation. The implantations of ASO device were successful in all of the 17 patients. Sixteen out of 17 (94.1%) had complete closure in the average observation period of 5.5 months. Complications were minimal and transient.

CONCLUSIONS

With respect to complete closure rate, easy manipulation, and complication rate, ASO is the best transcatheter ASD closure device among all the devices at the present time.

Centering-on-demand buttoned device: its role in transcatheter occlusion of atrial septal defects

Since the initial design and description of the buttoned device, it has undergone a number of design changes. Introduction of radiopacity in the knot (button) made it easier to visualize and document that buttoning has indeed occurred. Introduction of two buttons has markedly decreased the unbuttoning rate with potential for eliminating it. A centering mechanism was then incorporated into the device, which allowed closure of larger defects and use of smaller-sized devices. For some unknown reason, unbuttoning rate no longer occurs since the introduction of this device. The centering-on-demand (COD) device also appears to have increased the effective occlusion rates. At the present time, however, no long-term follow-up data are available to assess the long-term efficacy of the new device. Experience in a larger number of patients and evaluation of follow-up data are necessary to confirm the safety and efficacy observed in the small cohort reported in this review.

Transvenous closure of moderate and large secundum atrial septal defects in adults using the Amplatzer septal occluder

The aim was to determine the feasibility of using the Amplatzer septal occluder for closure of moderate and large secundum atrial septal defects in adults. Fifty patients aged 16-76 years (mean +/- SD, 40 +/- 15.5), underwent successful device implantation. Flow ratios of 1.4-8.5 (mean +/- SD, 2.6 +/- 1.6) were calculated. The defects were: centrally placed (n = 31), antero-superior with partial or total deficiency of aortic rim (n = 19), multiple (n = 3) and with aneurysmal septum (n = 23). They measured 4-25 mm (median 14) on echocardiography and balloon sized 7-31 mm (median 19.5). Devices of 7-34 mm (median 20) were implanted. Patient follow up for 1 month (50/50 patients), 3 months (40/50) and 12 months (13/50), achieved respective rates of 90%, 92% and 98% of complete occlusion. In one patient a transient atrioventricular block (2:1) developed, and one had a transient STT elevation. One female had an episode of 30 min loss of vision over the lateral aspect of the left eye 3 months after implantation. In conclusion, transvenous occlusion of secundum atrial septal defects with the Amplatzer septal occluder in adults is safe, and can be performed without significant complications. Large defects, defects with a very deficient or absent aortic rim, defects with an aneurysmal septum as well as some multiple defects can be closed with an almost 100% early complete occlusion rate. This makes the procedure an alternative to surgery for selected adult patients.

Early ECG abnormalities associated with transcatheter closure of atrial septal defects using the Amplatzer septal occluder

Conduction abnormalities and arrhythmias may occur in patients following secundum atrial septal defect (ASD) closure using the Amplatzer septal occluder (ASO). Therefore, the aim of this study was to prospectively perform ambulatory ECG monitoring to assess the electrocardiographic effects of transcatheter closure (TCC) of ASD using the ASO device. From 5/97 to 3/99, 41 patients with secundum ASD, underwent TCC using the ASO device at a median age of 9.2[emsp4 ]y. (0.5-87[emsp4 ]y.) and median weight of 34[emsp4 ]kg (5. 6-88[emsp4 ]kg.). Ambulatory Holter monitoring was performed pre- and immediately post TCC. Holter analysis included heart rate (HR), ECG intervals, supraventricular ectopy (SVE), ventricular ectopy (VE), and AV block. No change in baseline rhythm was noted in 37 patients (90%). Changes in AV conduction occurred in 3 patients (7%), including intermittent second degree AV block type II, and complete AV dissociation post closure. SVE was noted in 26 patients (63%) post closure, ranging from 5-2207 supraventricular premature beats (SVPB), including 9 patients (23%) with non-sustained supraventricular tachycardia (SVT), 3 of whom had short runs of SVT prior to closure. A significant increase in post-closure number of SVPB per hour (p=0.047) was noted. No significant difference was noted in PR interval, ventricular premature beats per hour, or QRS duration.

CONCLUSIONS

Based on ambulatory ECG analysis, TCC of ASD with the ASO device is associated with an acute increase in SVE and a small risk of AV conduction abnormalities, including complete heart block. Long term follow-up studies will be necessary to determine late arrhythmia prevalence and relative frequency compared with standard surgical ASD repair.

Experience in one centre using the buttoned device for occlusion of atrial septal defect: comparison with the Amplatzer septal occluder

We report our experience using the buttoned device to close defects within the oval fossa and probe-patent oval foramens, comparing the findings with those obtained with the Amplatzer septal occluder. From 1992 to 1997, we used the buttoned device to close defects in 73 consecutive patients, 64 with defects in the oval fossa and nine with patent foramens. We compared this experience with a further series of 62 patients seen from 1997 to 1999 in whom the Amplatzer septal occluder was used. Successful implantation was achieved in three-quarters of those with septal defects in whom the buttoned device was used, in all of those in whom the buttoned device was used for patent foramens, and in nine-tenths of those in whom closure was attempted using the Amplatzer occluder. Immediate surgery was needed in 3 patients in whom a buttoned device was used, one because of embolization and two with residual shunts and a straddling device. Similar immediate surgery was needed to retrieve one embolized Amplatzer occluder. During follow-up, surgery was needed in a further 7 patients, all having had insertion of a buttoned device, because of atrial perforation in one and a significant residual shunt in the remainder. At late follow-up, the rate of complete occlusion was 69% in the patients in whom the buttoned device was used to close a septal defect, 100% when the buttoned device was used for patent foramens, and 95% in those treated with the Amplatzer occluder. Our experience shows that the Amplatzer occluder produced a significantly higher rate of occlusion for larger defects, and with a shorter fluoroscopy time than the buttoned device. The Amplatzer septal occluder, therefore, is our preferred device for closure of defects within the oval fossa.

Transcatheter occlusion of complex atrial septal defects

Percutaneous device occlusion of secundum atrial septal defects (ASDs) is becoming an accepted alternative to surgical closure. This method allows us to evaluate patients with complex conditions for treatment. From a total of 70 patients with ASD evaluated for percutaneous closure, we selected for analysis 28 who had complex conditions. The mean age was 36+/-23 yr (range, 4-72). Six had heart failure, and of these six, three had atrial fibrillation. At cardiac catheterization, the pulmonary pressure was 47+/-24 mm Hg, and the QP/QS was 1.7+/-0.4; two patients had bidirectional shunt and systemic pulmonary pressure. Two patients received a buttoned device and 26 an Amplatzer septal occluder. The groups of patients with complex conditions were separated into the following groups. Group I (n = 4) underwent combined treatment of associated anomalies. Two patients had pulmonary stenosis, one had mitral stenosis, and one had an aortic root-left atrium fistula. They were treated in or during with the same procedure by combined transcatheter techniques (balloon valvuloplasty and fistula occlusion) before ASD occlusion. Group II (n = 9) had multiple defects (cribiform or two separate holes). They were treated with a single device in five instances and with two separate devices in four cases. Group III (n = 14) had large (32+/-3 mm) single defects. Nine of them underwent successful implantation using a device 33+/-3 mm in diameter; in the remaining five patients the device was removed because of instability. Group IV (n = 3) had residual defects after previous partial device occlusion. All three defects were successfully occluded with a second device. No movement or interference with the first device was observed. Group V (n = 6) had severe pulmonary hypertension (86+/-16 mm Hg). Immediately after ASD occlusion we observed significant relief in these patients (67+/-14 mm Hg; P<0.01). There were no major complications; all 23 patients with successful implants were discharged without symptoms 2-7 days later; one patient with atrial fibrillation recovered sinus rhythm. The follow-up (8+/-5 mo) Doppler echo study showed complete ASD occlusion in 22 patients and a peak pulmonary pressure of 30+/-14 mm Hg. We conclude that transcatheter occlusion of ASDs is an effective and safe treatment for patients with complex anatomic or physiopathologic conditions, as evaluated by short-term follow-up.

Results of transvenous occlusion of secundum atrial septal defects with the fourth generation buttoned device: comparison with first, second and third generation devices. International Buttoned Device Trial Group

OBJECTIVES

The purpose of this study was to assess safety and effectiveness of the fourth generation buttoned device in dosing atrial septal defects (ASDs) and to test the hypothesis that introduction of double button reduces unbuttoning rate without reducing effectiveness.

BACKGROUND

Because of the high unbuttoning rate (7.2%) with first, second and third generation buttoned devices, the device was modified (fourth generation) so that there were two radiopaque spring buttons 4 mm apart on the button loop attached to the occluder.

METHODS

During a four-year period ending in September 1997, 423 patients, ages 1.5 to 80 years (median 16 years), underwent closure of ASD at 40 medical centers around the world.

RESULTS

The ASD size varied between 5 and 30 mm (median 17 mm). The device size varied between 25 and 60 mm. Unbuttoning occurred in 4 (0.9%) of 423 patients. Effective occlusion, defined as no (n = 343) or trivial (n = 34) residual shunt on echo-Doppler studies performed within 24 h of the procedure, was demonstrated in 377 patients (90%). Thus, the unbuttoning rate (0.9 vs. 7.2%) decreased (p<0.01) while effective occlusion rate (90 vs. 92%) remained unchanged (p>0.1) with this device, compared with earlier generation devices. During follow-up from one month to five years (23+/-15 months), 21 (5%) of 417 patients required surgical (n = 12) or transcatheter (n = 9) reintervention, mostly to treat significant residual shunt. In the remaining patients there was gradual reduction and disappearance of the residual shunt. No wire integrity problems were observed.

CONCLUSIONS

These data suggest that the fourth generation buttoned device is as effective as earlier generation devices, but without significant unbuttoning. Follow-up results remained good, with a reintervention-free rate of 89% at five years.

Transcatheter closure of atrial septal defect with a CardioSEAL device

Transcatheter closure of an interatrial septal defect (ASD) with a CardioSEAL device was successfully performed on 12 Taiwanese children. There were five boys and seven girls, aged from 3.6-13.9 (8.3+/-3.2) years and with body weight of 15-57 (33.7+/-14.7) kgs. After one year of follow-up studies, which included physical examination, ECG, chest X-ray and echocardiography, complete closure of ASD was achieved in nine (75%) patients. Two children with a trivial residual shunt were asymptomatic and without audible cardiac murmur. A girl had a small residual left to right atrial shunt by color Doppler echocardiography, but without audible cardiac murmur. There were no immediate or intermediate complications. Transcatheter implantation of the CardioSEAL device is a safe and proper treatment for children with non-complicated small to medium secundum ASD.

Interventional pediatric cardiology: device closures

Surgical treatment of various septal defects has been long established. With the advances in transcatheter therapy dilatation techniques for valvular stenosis and vascular obstruction have become established procedures. Closure of septal defects in the catheterization laboratory has also been introduced; some of these have come into regular use in current practice. In 1967, Porstmann et al reported the use of Ivalon plug to close patent ductus arteriosus (PDA). Since then, several devices have been used including Rashkind PDA ocluder (not being used now), Gianturco coils, detachable coils (for small PDA), CardioSEAL and other umbrella devices and Amplatzer PDA occluder. Closure rates vary from 95-98% in most series, however, some of these devices are very expensive, more so, when compared to the cost of surgical ligation of PDA. Catheter closure of secundum atrial septal defect (ASD) has also been done by various devices like clamshell device, Sideris Buttoned device, ASDOS device, Amplatzer device and cardioSEAL. So far no device has been accepted as ideal for every case, however, Amplatzer device has been used most extensively. Issues such as completeness of endothelialisation, incidence of late arrhythmias, endocarditis remain uncertain. However, in select population of ASD cases with a central secundum defect, device closure is being used increasingly. Device closure of ventricular septal defect remains challenging and controversial and is probably available to a small group of children with defects that are difficult to close surgically and involve higher risk.

Sudden death in patients after transcatheter device implantation for congenital heart disease

To explore whether transcatheter intracardiac devices increase risk for sudden death, we analyzed patient and device-related variables with a case-control design. Sudden death was defined as unexpected death with abrupt onset and rapid deterioration. Cases included all patients known to have died suddenly after device closure at our institution, using 3 large databases. Controls (2:1), matched on year of procedure, were chosen randomly from the same databases. Data were obtained from medical record review. Of 777 patients who received implants between February 1989 and February 1999, 9 were known to have died suddenly (1.2%). In 27 cases and controls, diverse defects were occluded: atrial (n = 16), ventricular (n = 4), Fontan fenestration (n = 4), or other (n = 3). Cases were more likely to have had a history of serious arrhythmias (p = 0.008), severe valve regurgitation (p = 0.03), > or =1 cardiac surgery (p = 0.009), and multiple devices (p = 0.03). Cases were somewhat more likely to have pulmonary hypertension (p = 0.09), ventricular dysfunction (p = 0.09), and nonatrial septal defects (p = 0.10). Patients were less likely to have device arm fractures (p = 0.05). The following were not related to sudden death: age, weight, gender, low systemic cardiac index, end-diastolic pressure, major noncardiac disease, serious adverse events, maximum device size, malposition, and residual leak. This study suggests that sudden death was more likely to occur in device-implanted patients who had severe underlying cardiac disease and/or multiple devices. No other device-related variables were associated with sudden death.

The echocardiographic diagnosis, characterization, and extraction guidance of cardiac foreign bodies

Echocardiography is ideal for localizing cardiac foreign bodies and for characterizing associated cardiac and vascular injury before and during extraction. We report 5 cases of traumatic and iatrogenic cardiac foreign bodies that illustrate the central role of transthoracic and transesophageal ultrasonography in the management of these patients.

Transcatheter closure of atrial-septal defects and patent foramen ovale in adults: optimal anatomic adaptation of occlusion device

BACKGROUND

For transcatheter closure of atrial-septal defects, different occlusion systems are available. The purpose of this study was to examine the clinical feasibility of the ASD Occlusion System (ASDOS, Dr Osypka GmbH, Grenzach-Wyhlen, Germany) and to evaluate the short- and long-term results.

METHODS AND RESULTS

The study was composed of 20 consecutive patients with atrial-septal secundum defect (n = 13) or patent foramen ovale (n = 7). The device implantation was successful in all patients. For optimal closure of the defect, left atrial and right atrial umbrellas of different sizes were required in 10 of 20 patients. No major short- or long-term complications occurred. During the mean follow-up period of 13.9 +/- 5 months, 5 strut fractures without dislocation were observed, and in 8 (40%) of 20 patients transesophageal echocardiography revealed a small residual shunt.

CONCLUSION

The ASDOS double umbrella system is suitable for transcatheter closure of interatrial defects in selected patients. This system showed a high procedural safety and has the unique advantage of individual adaptation of the occluding device on the defect anatomy that results in high closure effectiveness.

Definitive percutaneous treatment of Lutembacher's syndrome

Definitive percutaneous treatment of a patient with Lutembacher's syndrome was successfully accomplished using the Amplatzer septal occluder to close a secundum atrial septal defect and the Joseph mitral balloon catheter to dilate rheumatic mitral valve stenosis. Transcatheter therapy is an effective alternative to surgery in selected patients with Lutembacher's syndrome. Cathet. Cardiovasc. Intervent. 48:199-204, 1999.

[Interventions in congenital heart disease and their sequelae in adults]

The advancements of cardiac surgery over the last decades led to larger numbers of patients with operated congenital heart diseases surviving into adulthood. In Germany it is estimated that over 120,000 adults have operated congenital heart diseases. Five to 7% of them will need yearly hospital admissions. Interventional procedures are additional tools used to treat these patients with various sequelae or residua (Table 1). In the following review we concentrate on 2 different interventional procedures: dilatation and stent implantations for treatment of stenosis and the different devices used for the closure of shunt lesions. For congenital valvular pulmonary stenosis, balloon dilatation is the therapy of choice regardless the age of the patient. Stent implantation for the treatment of peripheral pulmonary stenosis (e.g., after previous systemic pulmonary shunts) can decrease the need for redo surgery, which is accompanied with increased risk. Stent implantations proved also to be useful to treat stenoses after Mustard patch in patients with transposition of the great arteries, after Fontan procedures or dealing with the rare pulmonary venous stenosis. In contrast, dilatation of bioprosthesis and conduit stenosis are not promising. Balloon dilatation of valvular aortic stenosis is an accepted therapy in childhood up to adolescents. Table 2 compares a surgical series including many infants with critical aortic stenosis with a series of balloon dilatation in children and another one in adults regarding lethality, complications, and results. Table 3 illustrates the immediate and late results of balloon dilatation of aortic coarctation in 3 different studies. The high recurrence rate in infants made clinicians refrain from taking this age group for balloon dilatation. In children and adult patients, good results are reported (75% reduction of gradients). The complication rate is low (2.3 to 3.3%) and aneurysm formation rate seldom (1 to 7%). Stenosed aorto-pulmonary collaterals will rarely need balloon dilatation. Surgical closure of atrial septal defect is a low risk procedure with a very low rate of residual shunts (2%). Of the 5 available devices for transcatheter closure of atrial septal defect Type II, only 2 occluders are in use in Germany, the Clamshell and the Amplatzer device. The largest clinical studies of the different systems, their efficacy, complications and residual shunt rate are presented in Table 4. For the deployment of these occluders a TEE is always needed. There are many more systems in clinical use to close the patent arterial duct (PDA) (Table 5). The Ivalon plug as well as the Rashkind device have probably only historical value. Different types of coils (Gianturco, Cook detachable, PFM) are now in use worldwide. The reason for their widespread use, besides their easy application, is the fact that most coils are relatively cheap and need only small sheaths for deployment. Their further evaluation identified a residual shunt rate of 5% as well as a number of complications (embolization, hemolysis, stenosis of the left pulmonary artery) in 0 to 6%. For the large PDA the Amplatzer device has recently been introduced. An additional indication for the use of the different occluding devices are aorto-pulmonary collaterals, venovenous fistulae, pulmonary or coronary artery fistulae. Aorto-pulmonary collaterals are often associated with complex cardiac lesions and occasionally appear after palliative procedures. An excellent cooperation between adult and pediatric cardiologists is needed in order to offer the group of adults with congenital heart diseases an adequate and comprehensive management.

Recent advances in interventional pediatric cardiovascular disease

Transcatheter therapy in children with congenital or acquired heart disease is a challenging, innovative, and constantly evolving field. In this article we review the various "nonsurgical" techniques that are currently available, with a discussion of their applications and an update on the recent advances in the field of interventional cardiology.