Functionless retained pacing leads in the cardiovascular system. A complication of pacemaker treatment

Upper Extremity Deep Vein Thrombosis and Asymptomatic Vein Occlusion in Patients With Transvenous Leads: A Systematic Review and Meta-Analysis

Aims: The presence of transvenous leads for cardiac device therapy may increase the risk of venous thromboembolisms. The epidemiology of these complications has not yet been determined systematically. Therefore, this study aims to determine (I) the incidence of symptomatic upper extremity deep vein thrombosis (UEDVT) and (II) the prevalence of asymptomatic upper extremity vein occlusion in patients with transvenous leads, both after the initial 2 months following lead implantation.

Methods: PubMed, EMBASE, and Cochrane Library were searched until March 31, 2020 to identify studies reporting incidence of UEDVT and prevalence of asymptomatic vein occlusion after the initial 2 months after implantation in adult patients with transvenous leads. Incidence per 100 patient years of follow-up (PY) and proportions (%) were calculated to derive pooled estimates of incidence and prevalence.

Results: Search and selection yielded 20 and 24 studies reporting on UEDVT and asymptomatic vein occlusion, respectively. The overall pooled incidence of UEDVT was 0.9 (95% CI 0.5–1.4) per 100PY after 2 months after lead implantation. High statistical heterogeneity was present among studies (I² = 82.4%; P = < 0.001) and only three studies considered to be at low risk of bias. The overall pooled prevalence of asymptomatic upper extremity vein occlusion was 8.6% (95% CI 6.0–11.5) with high heterogeneity (I² = 81.4%; P = <0.001). Meta-regression analysis showed more leads to be associated with a higher risk of UEDVT.

Conclusion: Transvenous leads are an important risk factor for symptomatic UEDVT, which may occur up to multiple years after initial lead implantation. Existing data on UEDVT after lead implantation is mostly of poor quality, which emphasizes the need for high quality prospective research. Asymptomatic vein occlusion is present in a substantial proportion of patients and may complicate any future lead addition.

Clinical Trial Registration: (URL: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020178136, Identifier: PROSPERO 2020 CRD42020178136).

Frequency and clinical impact of retained implantable cardioverter defibrillator lead materials in heart transplant recipients

End-stage heart failure patients with implantable cardioverter-defibrillator (ICD) with/without cardiac resynchronization therapy (CRT-D) often require heart transplantation (HTPL) as a last-resort treatment. We aimed to assess the frequency and clinical impact of retained ICD lead materials in HTPL patients. In this retrospective single center study, we examined the clinical records and chest radiographs of patients with ICD and CRT-D who underwent HTPL between January 1992 and July 2014. Of 40 patients with ICD and CRT-D at HTPL, 19 (47.5%) patients had retained ICD lead materials within the central venous system. Retained ICD lead materials following HTPL were more frequently noted in patients with longer implantation durations until HTPL. None of the patients underwent extraction procedures after HTPL. All patients were asymptomatic and did not exhibit significant complications or death related to the retained ICD lead materials. Seven (7/40, 17.5%) patients without any retained ICD lead materials underwent magnetic resonance imaging (MRI) during the follow-up period (median, 29.5 months); none of the patients with retained lead materials were given MRI. Considering the common use of MRI in HTPL patients, further studies on the prophylactic extraction of retained ICD lead materials and safety of MRI in these patients are needed.

Septic Pulmonary Embolism Caused by Infected Pacemaker Leads After Replacement of a Cardiac Resynchronization Therapy Device

BACKGROUND Cardiac resynchronization therapy (CRT) has been demonstrated to reduce morbidity and mortality in patients with advanced, drug-refractory heart failure. Procedure-related mortality is less than 1% in larger studies. Approximately10% of CRT patients have to undergo surgical revision because of infections, dislocations, or unacceptable electrical behavior manifested as high threshold, unstable sensing, or unwanted phrenic nerve stimulation. CASE REPORT A 70-year-old man with symptomatic congestive heart failure underwent implantation of a biventricular pacemaker on the left anterior chest wall in 2003 and pulse generator exchange in August 2009. The patient responded well to CRT. At follow-up, the pacing system functioned normally. In September 2009, in the context of a predialysis program, an abdominal computed tomography (CT) scan was performed in another hospital for assessment and evaluation of chronic kidney disease. This procedure was complicated with peripheral thrombophlebitis that was managed appropriately with complete recovery. Eight months later (May 2010), the patient was admitted to our hospital with fever, anemia, and elevated infection parameters. During admission, blood cultures grew Staphylococcus epidermidis. The chest X-ray, lung perfusion scintigraphy, and CT scan depicted pulmonary embolism and infarction. The right ventricular lead threshold was found to be increased to 7 volts with unsuccessful capture. Echocardiography demonstrated vegetations on leads. The entire pacing system was explanted, but the patient expired few days later following percutaneous removal due to multiorgan failure. CONCLUSIONS In heart failure, replacement of the CRT device may be complicated by bacterial endocarditis. As noted from this case report, sudden elevation of the pacing lead threshold should prompt thorough and immediate investigation to unravel its causes, not only the electrical characteristics but also the anatomical features.

Foreign bodies in the heart

BACKGROUND

Foreign bodies in the heart are rare, may reach the heart by different ways, and cause serious complications. X-ray, computerized tomography, and echocardiography are main diagnostic modalities. Foreign body can be removed surgically, percutaneously or can be managed conservatively. In this work, we analyzed 100 published cases of a foreign body in the heart and 4 cases that were identified in our hospital.

METHODS

We searched the literature for foreign body in the heart and found 100 published previously cases. Additional 4 cases were identified in our echo laboratory. A total series of 104 patients with a foreign body in the heart were analyzed for the etiology, clinical presentation, symptoms, complications and management.

RESULTS

Mean patients' age was 46, there were more men than woman 73 versus 31 [P < 0.00005]. The most common foreign bodies were parts of inferior vena cava filters and devices implanted for relieving hydrocephalus. Foreign bodies in the heart were symptomatic in 56% of patients. Right heart chambers were occupied more often. A total of 20% presented within the first 24 hours and 30% of patients presented years after the penetration of the foreign body. A majority of foreign bodies reached the heart by migration [88%]. Mortality was reported in 4 patients [3.8%]. Here 54% of the patients underwent surgical and 29% percutaneous removal of the foreign body, while 14% were followed conservatively.

CONCLUSION

Foreign bodies in the heart may present with a wide variety of symptoms. Physicians should be aware of this rare and peculiar complications which may be fatal. Larger devices may result in more severe complications.

Transvenous removal of pacing and implantable cardiac defibrillating leads using single sheath mechanical dilatation and multiple venous approaches: high success rate and safety in more than 2000 leads

AIMS

The aim of the present study was to describe a 10 years single-centre experience in pacing and defibrillating leads removal using an effective and safe modified mechanical dilatation technique.

METHODS AND RESULTS

We developed a single mechanical dilating sheath extraction technique with multiple venous entry site approaches. We performed a venous entry site approach (VEA) in cases of exposed leads and an alternative transvenous femoral approach (TFA) combined with an internal transjugular approach (ITA) in the presence of very tight binding sites causing failure of VEA extraction or in cases of free-floating leads. We attempted to remove 2062 leads [1825 pacing and 237 implantable cardiac defibrillating (ICD) leads; 1989 exposed at the venous entry site and 73 free-floating] in 1193 consecutive patients. The VEA was effective in 1799 leads, the TFA in 28, and the ITA in 205; in the overall population, we completely removed 2032 leads (98.4%), partially removed 18 (0.9%), and failed to remove 12 leads (0.6%). Major complications were observed in eight patients (0.7%), causing three deaths (0.3%).

CONCLUSION

Mechanical single sheath extraction technique with multiple venous entry site approaches is effective, safe, and with a good cost effective profile for pacing and ICD leads removal.

Bacteremia caused by late-infected pacemaker lead--a case report

A 73-year-old man with bradycardia and atrial fibrillation underwent implantation of a transvenous pacemaker system on the left anterior chest wall in 1995. Six years later, he was admitted for bacteremia from coagulase-negative Staphylococcus. Repeated treatment employing antibiotic therapy was ineffective. The infected electrode was removed under cardiopulmonary bypass. His electrode had become firmly encased with fibrous tissue within the right ventricle and atrium. It was removed under direct vision during complete cardiac arrest. The postoperative course was uneventful and there has been no recurrence after 1 year.

The postmodern heart: war veterans' experiences of invasive cardiac technology

BACKGROUND

The consequences of war and medical discourse have historical connections to pacemaker technology. Understanding these consequences is important because war veterans, medicine and cardiac technology have a shared history that continues into the present. The incidence of Australian war veterans needing cardiac pacemakers has increased many-fold in recent years, due to advancing age. This need was recognized by the Australian Department of Veteran Affairs and a cardiac programme was established in the veteran hospital that was the setting for this study.

AIM

This paper reports on a study aimed at capturing the interest and sensitizing the practice of nurses involved in the care of war veterans and other health care consumers who have been diagnosed as requiring a cardiac pacemaker. The study sought to answer the question, 'How does the war veteran experience his body in relation to invasive cardiac technology?'.

METHOD

The research was guided by the principles of interpretive interactionism, and used unstructured interviews with eight male war veterans. The data were collected in 2000.

FINDINGS

Thematic and content analysis revealed five themes: emotional knowing; the medical encounter; belief in the myth of miracle; technological constraint; and the altered heart. The findings indicated that the human dimension was characterized by experiences of ambivalence, inner conflict, powerlessness and suffering.

CONCLUSION

Nursing is at the interface of science and patient care, and this study contributes to nursing knowledge by focusing on a previously unresearched topic, namely embodied interactions between war veterans and invasive cardiac pacemakers. Within a highly technical area such as cardiology, nurses can still work around the technology and keep patients as their primary focus, thus promoting quality care. A humanistic rather than a technological focus locates nurses between patients and cardiac technology. In this in-between location, nurses are not an extension of cardiac technology but a valuable source of information, education, and counselling.

Is there an adverse outcome from abandoned pacing leads?

BACKGROUND

Indications for extraction of an abandoned pacemaker lead (APL) are controversial. The purpose of this study was to determine whether or not APLs should be extracted in the absence of pacemaker-related problems.

METHODS AND RESULTS

We retrospectively reviewed, from 1977 through 1998, all patients with retained, non-functional leads and identified 433-266 males and 167 females. Mean age at initial pacemaker implantation was 68[emsp4 ]years. These patients received a total of 259 atrial and 948 ventricular leads. Of the total of 1,207 leads, 611 became non-functional. A total of 531 non-functional leads were abandoned, of which 18 were later extracted: one APL in 345 patients, two in 78, and three in 10. Indications for new lead placement when non-functional leads were abandoned included capture and/or sensing failure (243), lead recall (177), lead fracture (86), pacing system replacement to the contralateral side (11), accommodating patient growth (5), pacemaker function upgrade (5), replacement with implantable cardioverter defibrillator (ICD, 2), interference with ICD (1), and unknown (1). Complications that were associated with pacemakers were found in 24 patients (5.5%)-pacemaker system infection (8 patients) and venous occlusion at the time of a subsequent procedure of new lead placement when APLs had already been in place (16) which resulted in APL extraction (7) or transfer of the pacemaker system to the contralateral side (9). Neither venous thrombosis nor other complications were found in the remaining 409 patients (94.5%). The incidence of complications was higher in patients with three APLs than in patients with two or fewer APLs (40% vs. 4.7%, P=1x10(-6)), in patients with four or more total lead implantations than in patients with three or fewer total lead implantations (26.2% vs. 0. 6%, P<1x10(-10)), and in patients with three or more procedures of new lead placements than in patients with two or fewer procedures of new lead placements (36.4% vs. 3.9%, P=1x10(-10)). Patients with complications were younger than those without complications both at the time of initial pacemaker implantation (59+/-16 vs. 68+/-17 y, P=0.01) and when non-functional leads were abandoned (63+/-15 vs. 71+/-16 y, P=0.04). Mean numbers of APLs, total leads implanted, and procedures of new lead placement were significantly larger in patients with complications than in those without complications (1.58+/-0.78 vs. 1.2+/-0.44, 4.96+/-1.23 vs. 2.66+/-0.8, and 2.13+/-0.85 vs. 1.25+/-0.53, P=0.03, 4x10(-9) and 4x10(-5), respectively).

CONCLUSIONS

1. With only 5.5% of patients having had pacemaker-related complications, the adverse outcome of APL is small. 2. Clinical clues to the possible occasion for pacemaker-related complications include three or more APLs, four or more total leads, three or more procedures of new lead placement, and a younger age at initial pacemaker implantation. 3. Patients with a large number of APLs, total lead implantations, and procedures of new lead placement should be carefully observed to detect possible pacemaker-associated complications.

Peripheral pulmonary migration of a retained pacemaker lead

We report a case of lead migration into the right middle pulmonary lobe. The migrated electrode reached the pleura and produced severe pleural symptoms, therefore, surgical removal of the retained lead was required. This case report demonstrates the importance of a chest X ray in the follow-up of patients with an implanted pacemaker to detect complications like lead fracture or migration.

Role of transesophageal echocardiography in the diagnosis of infected retained pacing lead

A 68-year-old woman had a transvenous pacemaker implanted 6 years ago. One year after the procedure the pulse generator was removed due to generator site infection. Efforts to remove the lead resulted in fracture of the tip, which was abandoned in the right cardiac cavities. After this the patient suffered intermittent episodes of fever and chills, which responded to antibiotic therapy. At her recent admission, transesophageal echocardiography revealed a large mass attached to the free end of the fractured lead suggestive of the existence of a vegetation on the pacing lead. The diagnosis was confirmed at surgery.

Extraction and replacement of permanent pacemaker leads through occluded vessels: use of extraction sheaths as conduits--balloon venoplasty as an adjunct

Patients (pts) may present for lead extraction with symptomatic or asymptomatic subclavian vein or superior vena cava thrombosis. Replacement of permanent pacemaker leads (PPLs) in these pts may be difficult and may require accessing a new site. We examined the utility of replacing PPLs through completely occluded vessels using extraction sheaths as conduits through the total occlusion. Over six years, a total of 210 atrial and/or ventricular PPLs were extracted from 137 pts. Two pts presented with angiographically documented thrombotic occlusion of the subclavian vein. One additional pt. who had presented with a superior vena cava (SVC) syndrome, had a totally occluded innominate vein and SVC occlusion. Balloon venoplasty was used as an adjunct to dilate the SVC. In all pts, after PPLs were removed via a subclavian extraction sheath through the occluded vessel, the retained sheath was used to place a guide wire, then a peel away dilating sheath, to insert new PPLs, in each case on the side of total venous occlusion. Seven PPLs and two lead fragments were extracted, and five new PPLs replaced, ipsilateral to the venous occlusion. These data show that extraction of PPLs through thrombosed veins may be performed successfully and may not require replacing the leads through a new site. This technique spares the pt the need to access the opposite subclavian vein, and it avoids an excessive number of PPLs in the subclavian vein and SVC. The procedure illustrates an efficient means to reintroduce new PPLs with the potential to reduce associated morbidity, since repeat puncture of the subclavian vein is not required. Safety of the procedure as a whole must be considered with regard to the known risks of lead extraction, some complications of which may be substantial using current techniques.

Intravascular extraction of chronic pacemaker leads: efficacy and follow-up

Extraction of chronic pacemaker leads has been recommended for infections, prevention of venous thrombosis, migration, and possible perforation. Success with constant traction techniques has been variable, and the cost and morbidity of open chest surgical procedures are prohibitive. Efficacy of a new system for lead extraction using intravascular techniques was analyzed. The system (Cook Pacemaker) uses a locking stylet, which is secured at the distal electrode by counterclockwise rotation to reinforce the lead and facilitate traction, and dilator sheaths that are used to free the lead from adhesions in the venous system. In a series of 56 patients (ages 19-88) who presented for lead extraction because of erosion (5), infection (14), lead replacement (35), or other (2), 86 leads were extracted. Thirty-two were atrial leads and 54 ventricular; 23 had active fixation and 63 passive. Average duration of implant was 58 +/- 42 months (range 1-264). Eighty-four leads were totally removed and two partially removed. For these two leads, the distal tip was not removed; in both cases the locking stylet was not secured at the distal electrode due to obstruction within the lead. Two patients developed arm edema following the procedure, which resolved with elevation. One patient developed a subclavian thrombosis, which resolved with warfarin anticoagulation. Four patients have expired due to unrelated causes. In conclusion, this intravascular approach for extraction of chronic leads is effective, and the procedure is safe when performed by experienced personnel.

Surgical removal of infected transvenous pacemaker leads

Infection, though uncommon, can be the most lethal of all potential complications following transvenous pacemaker implantation. Eradication of infection associated with pacemakers requires complete removal of all hardware, including inactive leads. Since 1972, 5,089 patients have had 8,508 pacemaker generators implanted at Montefiore Medical Center. There were 91 infections (1.06%); four of our patients required surgical removal. Nine additional patients were referred for surgical removal of infected transvenous pacemaker leads from other institutions. Surgical methods for removal included use of cardiopulmonary bypass or inflow occlusion. Surgery may be safely used in unstable or elderly patients and should not be reserved as a last resort. This article reviews our surgical experience removing infected pacemaker leads at Montefiore Medical Center.

Superior vena cava occlusion and/or syndrome related to pacemaker leads

Four cases of pacemaker-related SVC obstruction or syndrome are reported. While two of them lacked any symptom suggestive of SVC obstruction, the other two presented with mild symptoms. None of them received any treatment. One died from a cause unrelated to SVC obstruction, while the others presented no change in their clinical status. A review of the literature suggests that neither thrombotic nor fibrotic obstruction in patients with pacemaker leads is strictly related to the number of abandoned leads, the presence of severed leads, or the time elapsing from pacemaker implant. The diagnosis is clinically made and is confirmed by venography. Only one of the reported deaths is attributable to SVC obstruction. The remaining cases from the literature responded to treatment with heparin, thrombolytic agents, angioplasty, or surgery.

Infected endocardial pacemaker electrodes: successful open intracardiac removal

The long-term results after open intracardiac removal of infected pacing electrodes are presented.

METHODS

Between 1985 and 1990 open intracardiac removal of 19 infected pacing electrodes was performed in seven patients (six male and one female), with a mean age of 56 years. The indications were: persisting bacteremia in three; generator pocket infection in four; endocarditis in one; and ventricular tachycardia caused by retracted electrodes in one. All electrodes were fixed in the right heart and extraction by closed methods failed. Percutaneous catheter techniques were not applied in these seven patients. In five patients two ventricular electrodes had to be removed, and in two patients a single one. A total of seven atrial electrodes were removed in six patients (one electrode each in five patients; two electrodes in one patient). All atrial and two ventricular electrodes could be removed through a pursestring suture without use of a pump oxygenator. For the removal of ten ventricular electrodes in six patients (two electrodes each in four patients; 1 electrode each in two patients) a right-sided atriotomy was necessary with cardiopulmonary bypass (CPB). Simultaneously, five new pacing systems were implanted.

RESULTS

There were no early or late mortalities. In January 1991, all seven patients are alive and in a mean New York Heart Association Class 1,3 of heart failure after a mean interval of 33 months. In all cases the infection could controlled with a simultaneous antimicrobial chemotherapy and the postoperative period was free of major complications.

CONCLUSION

Open intracardiac removal of retained pacing electrodes with or without use of CPB is a safe procedure without major complications. It is mandatory for all infected pacing electrodes that cannot be extracted by closed methods.

Venous complications after insertion of a transvenous pacemaker

We reviewed the incidence, clinical features, current diagnostic evaluations, and treatments of venous complications that can occur after implantation of a transvenous pacemaker. Of the approximately 80 published articles on the potential venous complications after implantation of a permanent transvenous pacemaker, we selected 63 that addressed the clinical features, diagnosis, and treatment of pacemaker lead-induced venous thrombosis, which occurs in approximately 30 to 45% of patients early or late after implantation of a transvenous pacemaker. Most patients with chronic deep venous thrombosis remain asymptomatic because of the development of an adequate venous collateral circulation. Clinical features of pacemaker lead-induced deep venous thrombosis, although rare, are easily recognized. They should be sought routinely during follow-up of all patients with transvenous pacemaker leads because venous obstruction can interfere with intravenously administered therapy, monitoring of central venous pressure, and revision of a pacemaker lead. Acute deep venous thrombosis is likely to be symptomatic. Early recognition and treatment of acute deep venous thrombosis may help to decrease the potential morbidity and mortality. The definitive diagnosis of pacemaker lead-induced venous thrombosis necessitates contrast-enhanced or digital subtraction venography. Management includes anticoagulation, thrombolytic therapy, surgical intervention, and, recently, percutaneous transluminal balloon venoplasty and depends on the duration, extent, and site of venous occlusion as well as the accompanying symptoms.

Myocardial Rupture After Pulling Out a Tined Atrial Electrode with Continuous Traction

Transvenous traction for the removal of retained pacemaker electrodes is common practice with few reported complications. This case reports a patient with a DDD pacemaker with extruded electrodes, who died of a myocardial rupture at the atrial lead site after prolonged (i.e., after 24 hours) traction was applied.

Extraction of implanted transvenous pacing leads: a review of a persistent clinical problem

Within a few months of implantation, permanent pacemaker leads become ensheathed in fibrocollagenous tissue. This tissue may anchor the lead so that it is difficult, dangerous, or impossible to remove it. Leads with bulbous or finned tips are particularly resistant to extraction. The risks of applying traction to an entrapped lead include induction of bradycardia or ventricular tachycardia and fibrillation, invagination of the right ventricle, avulsion of the right ventricular myocardium or tricuspid valve, hemopericardium, and cardiac tamponade. Forceful traction may result in uncoiling of the conductor, disruption of the insulation, or complete fracture, leaving an intravascular remnant that may embolize or be a source for thrombosis. Although fixation and abandonment of an inactive chronically implanted lead is frequently appropriate and is known to pose little long-term risk, the retained inactive lead may interact adversely with a new active lead and then increase the risk of venous thrombosis, serve as a potential nidus for infection, or produce spurious electrical sensing signals that may be sensed by the pulse generator. Absolute indications for lead removal are those in which there would be a life-threatening situation if the lead were to remain in situ. In the absence of an absolute indication, the decision to proceed with extraction must be made by weighing the potential for serious morbidity or mortality against risks of the extraction technique. Techniques for lead removal include traction and open cardiotomy operations. When a portion of the lead is intravascular, forceps, snares, baskets, countertraction, or lead-transection devices may be used to retrieve the fragment.

Chronic transvenous pacemaker lead removal using a unique, sequential transvenous system

Transvenous removal of 43 consecutive chronic pacemaker leads was successful in 28 patients. For leads not removed by traction at the pacemaker connection terminal, a unique locking stylet was advanced through the inner coil lumen and engaged at the tip to allow traction without lead elongation. Leads not extracted with the locking stylet alone had traction maintained on the stylet as sheaths were advanced over the lead to dilate and detach any fibrous tissue adherent to the lead. By applying traction at the pacemaker connection terminal, 2 leads were removed. The locking stylet alone extracted 9 leads. Both the locking stylet and sheaths were necessary to explant 32 leads. There were 15 right atrial and 22 right ventricular leads completely removed. Additionally, 6 right ventricular leads were subtotally removed leaving only the tip in the right ventricular apex. Avulsed myocardium was removed with the lead in 1 patient without sequelae. A subacute hemothorax developed in 1 patient 18 days after discharge requiring drainage, and subclavian vein thrombosis developed in another, which was successfully treated with anticoagulation. Hypotension occurred in 1 patient during final positioning of new leads, which responded to conservative treatment. Chronic pacemaker leads can be reliably removed without thoracotomy. Both a unique locking stylet to allow traction without lead elongation and a sheath to dilate and detach adherent fibrous tissue are needed for consistent success. Recognized complications included myocardial avulsion without sequelae, subacute hemothorax, subclavian vein thrombosis and transient hypotension.

Pacemaker-induced superior vena cava syndrome: report of four cases and review of the literature

Superior vena cava syndrome due to transvenous pacing leads is a rare event. We describe four cases. One occurred among 3,100 primary pacemaker insertions performed at our institution. In the other three cases the primary insertion had been performed elsewhere. Over 30 cases have been reported previously. Local infection, which preceded the development of superior vena cava syndrome in each of our four cases, and the presence of a severed retained lead, as in three of our cases, are important predisposing factors. There is no strong evidence that multiple lead insertion, if each lead remains intact, significantly increases the risk. The pathology at the site of obstruction includes thrombosis and in some cases fibrotic narrowing. Venous angiography is useful to show the site of obstruction, the extent of collateral circulation and to assess the response to treatment. Treatment should include removal of any infected pacemaker apparatus, anticoagulation and, if symptoms are of recent onset, thrombolytic therapy. Most patients improve but in those who do not angioplasty or surgical relief of the obstruction may be helpful.