Graded balloon dilation atrial septostomy as a bridge to lung transplantation in pulmonary hypertension

Invited Article: Emerging soft bioelectronics for cardiac health diagnosis and treatment

Cardiovascular diseases are among the leading causes of death worldwide. Conventional technologies for diagnosing and treating lack the compliance and comfort necessary for those living with life-threatening conditions. Soft electronics presents a promising outlet for conformal, flexible, and stretchable devices that can overcome the mechanical mismatch that is often associated with conventional technologies. Here, we review the various methods in which electronics have been made flexible and stretchable, to better interface with the human body, both externally with the skin and internally with the outer surface of the heart. Then, we review soft, wearable, noninvasive heart monitors designed to be attached to the chest or other parts of the body for mechano-acoustic and electrophysiological sensing. A common method of treatment for various abnormal heart rhythms involves catheter ablation procedures and we review the current soft bioelectronics that can be placed on the balloon or head of the catheter. Cardiac mapping is integral to determine the state of the heart; we discuss the various parameters for sensing aside from electrophysiological sensing, such as temperature, pH, strain, and tactile sensing. Finally, we review the soft devices that harvest energy from the natural and spontaneous beating of the heart by converting its mechanical motion into electrical energy to power implants.

Interventional Therapies in Pulmonary Hypertension

Despite advances in drug therapy, pulmonary hypertension-particularly arterial hypertension (PAH)-remains a fatal disease. Untreatable right heart failure (RHF) from PAH eventually ensues and remains a significant cause of death in these patients. Lowering pulmonary input impedance with different PAH-specific drugs is the obvious therapeutic target in RHF due to chronically increased afterload. However, potential clinical gain can also be expected from attempts to unload the right heart and increase systemic output. Atrial septostomy, Potts anastomosis, and pulmonary artery denervation are interventional procedures serving this purpose. Percutaneous balloon pulmonary angioplasty, another interventional therapy, has re-emerged in the last few years as a clear alternative for the management of patients with distal, inoperable, chronic thromboembolic pulmonary hypertension. The current review discusses the physiological background, experimental evidence, and potential clinical and hemodynamic benefits of all these interventional therapies regarding their use in the setting of RHF due to severe pulmonary hypertension.

Interventional and surgical therapeutic strategies for pulmonary arterial hypertension: Beyond palliative treatments

Despite significant advances in pharmacological treatments, pulmonary arterial hypertension remains an incurable disease with an unreasonably high morbidity and mortality. Although specific pharmacotherapies have shifted the survival curves of patients and improved exercise endurance as well as quality of life, it is also true that these pharmacological interventions are not always accessible (particularly in developing countries) and, perhaps most importantly, not all patients respond similarly to these drugs. Furthermore, many patients will continue to deteriorate and will eventually require an additional, non-pharmacological, intervention. In this review we analyze the role of atrial septostomy and Potts anastomosis in the management of patients with pulmonary arterial hypertension, we summarize the current worldwide clinical experience (case reports and case series), and discuss why these interventional/surgical strategies might have a therapeutic role beyond that of a "bridge" to transplantation.

Lung transplantation and atrial septostomy in pulmonary arterial hypertension

This article summarizes the current literature regarding surgical interventions in pulmonary hypertension, excluding chronic thromboembolic pulmonary hypertension. The article discusses the use of atrial septostomy in patients meeting criteria as well as single, double, and heart-lung transplantation.

Materials for multifunctional balloon catheters with capabilities in cardiac electrophysiological mapping and ablation therapy

Developing advanced surgical tools for minimally invasive procedures represents an activity of central importance to improving human health. A key challenge is in establishing biocompatible interfaces between the classes of semiconductor device and sensor technologies that might be most useful in this context and the soft, curvilinear surfaces of the body. This paper describes a solution based on materials that integrate directly with the thin elastic membranes of otherwise conventional balloon catheters, to provide diverse, multimodal functionality suitable for clinical use. As examples, we present sensors for measuring temperature, flow, tactile, optical and electrophysiological data, together with radiofrequency electrodes for controlled, local ablation of tissue. Use of such 'instrumented' balloon catheters in live animal models illustrates their operation, as well as their specific utility in cardiac ablation therapy. The same concepts can be applied to other substrates of interest, such as surgical gloves.

Surgical therapies for pulmonary arterial hypertension

Surgical therapies for the treatment of pulmonary arterial hypertension typically are reserved for patients who are deemed to be refractory to medical therapy and have evidence of progressive right-sided heart failure. Atrial septostomy, a primarily palliative procedure, may stave off hemodynamic collapse from right-sided heart failure long enough to permit a more definitive surgical treatment such as lung or combined heart-lung transplantation. This article discusses indications for and results of atrial septostomy and lung and heart-lung transplantation in patients who have pulmonary arterial hypertension.

Primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a rare disorder characterised by raised pulmonary-artery pressure in the absence of secondary causes. Precapillary pulmonary arteries are affected by medial hypertrophy, intimal fibrosis, microthrombosis, and plexiform lesions. Most individuals present with dyspnoea or evidence of right heart failure. Echocardiography is the best non-invasive test to screen for suspected pulmonary hypertension. The discovery of mutations in the coding region of the gene for bone morphogenetic protein receptor 2 in patients with familial and sporadic PPH may help not only to elucidate pathogenesis but also to direct future treatment options. The pathogenesis is not completely understood, but recent investigations have revealed many possible candidate modifier genes. Without treatment, the disorder progresses in most cases to right heart failure and death. With current therapies such as epoprostenol, progression of disease is slowed, but not halted. Many promising new therapeutic options, including prostacyclin analogues, endothelin-1-receptor antagonists, and phosphodiesterase inhibitors, improve clinical function and haemodynamic measures and may prolong survival.

Lung transplantation for primary pulmonary hypertension

Recent progress in medical therapies has diminished the role of transplantation in the management of PPH during the past decade. Drug therapy is not effective in some patients, responses to therapy are not sustained over time in others, and drug side effects eventually limit the benefits of treatment in a few more. Lung transplantation therefore ultimately is the only alternative for patients whose PPH is severe and cannot be managed medically. Choosing the right patient as a transplant candidate and the right time to make the initial referral to a transplant center are the crucial initial steps in the transplantation process, and the long waiting time before transplantation must be integrated into this decision. The outcome of lung and heart-lung transplantation for PHH has been good but sobering. Functional recovery has been excellent, but long-term survival results have been limited by the high prevalence of chronic allograft rejection.

Atrial septostomy for pulmonary hypertension

Atrial septostomy represents an additional, promising strategy in the treatment of severe PPH. Experience with this procedure still is limited; however, based on analyses of the worldwide experience, several general conclusions and recommendations can be made. 1. Atrial septostomy can be performed successfully in selected patients with advanced pulmonary vascular disease. 2. Patients with primary pulmonary hypertension who have undergone successful AS have shown: a significant clinical improvement beneficial and long-lasting hemodynamic effects at rest a trend toward improved survival 3. The procedure-related mortality of the collective experience is high (16%). Several recommendations can be made to minimize the risk: [figure: see text] Atrial septostomy should be attempted only in institutions with an established track record in the treatment of advanced pulmonary hypertension, where septostomy is performed with low morbidity. Atrial septostomy should not be performed in patients in whom death is impending or who have severe right ventricular failure and are on maximal cardiorespiratory support. An mRAP greater than 20 mm Hg, PVR index greater than 55 u/m2, and a predicted 1-year survival less than 40% are significant predictors of procedure-related death. Before cardiac catheterization, patients should have an acceptable baseline systemic oxygen saturation (> 90% in room air) and optimized cardiac function (adequate right heart filling pressure, additional inotropic support if necessary). During cardiac catheterization, the following are mandatory: Supplemental oxygen Mild sedation to prevent anxiety Careful monitoring of variables (left atrial pressure, SaO2, and mRAP) Step by step procedure After AS, it is important to optimize oxygen delivery. Transfusion of packed red blood cells or erythropoietin (before and following the procedure, if needed) may be necessary to increase oxygen content. 4. Because the disease process in PPH is unaffected by the procedure (late deaths), the long-term effects of an AS must be considered to be palliative. 5. Despite its risk, AS may represent a viable alternative for selected patients with severe PPH. Indications for the procedure may include: Recurrent syncope or right ventricular failure, despite maximal medical therapy, including oral calcium-channel blockers or continuous intravenous prostacyclin (Fig. 11) As a bridge to transplantation When no other option exists.

Echocardiographic Evaluation of Patients with Primary Pulmonary Hypertension Before and After Atrial Septostomy

OBJECTIVES: To characterize the early changes in right ventricular [right ventricle (RV)] geometry and function, as assessed by two-dimensional (2-D) and Doppler echocardiography, after balloon-dilation atrial septostomy (BDAS) in patients with severe primary pulmonary hypertension (PPH). BACKGROUND: Survival in PPH is to a great extent dependent on the functional status of the RV. BDAS recently has been shown to improve functional class and hemodynamics in patients with PPH nonresponsive to conventional vasodilator treatment. METHODS: Ten patients with severe PPH who underwent BDAS were studied with transthoracic and transesophageal 2-D and Doppler echocardiography. RV dimensions were measured in the apical four-chamber view. Continuous-wave Doppler echocardiography was used to obtain peak velocity of tricuspid regurgitation. Transesophageal echocardiography (TEE) primarily was used for the follow-up of the atrial septal defects (ASDs). RESULTS: In the early post-BDAS studies, right atrial and ventricular dimensions significantly decreased in all patients (P < 0.05). Global right ventricular wall motion (RVWM) also improved. RV percent change in area after septostomy inversely correlated with the changes in RV systolic area (r = -0.75; P < 0.05) and also with the baseline (preprocedure) values of RV percent change in area (r = -0.77; P < 0.05). Neither RV wall thickness nor the degree of tricuspid regurgitation were modified significantly after the procedure. CONCLUSIONS: BDAS in the setting of severe PPH results in moderate and salutary changes in geometry and function of the RV as assessed by 2-D echocardiography. These changes mainly appear to be the result of the decompression effect of atrial septostomy.

Atrial septostomy as a bridge to lung transplantation in patients with severe pulmonary hypertension

Long waiting times for lung transplantation have limited the survival of patients with advanced pulmonary hypertension. Atrial septostomy has been used in this group of patients in an attempt to prolong survival. We evaluated the results of atrial septostomy in 12 patients using the static graded balloon dilation technique. Between December 1990 and May 1998, 10 women and 2 men (ages 13 to 56 years, mean 37 years) underwent atrial septostomy. Nine patients had primary and 3 patents had secondary pulmonary hypertension. Five patients deteriorated despite long-term intravenous prostacyclin infusions. The atrial septum was crossed with a Brockenbrough needle, followed by an 0.035-J exchange wire and progressively larger catheter balloons for atrial septal dilation, until systemic oxygen saturation decreased 5% to 10%. An atrial septal defect was successfully created in each patient. The mean right atrial pressure decreased from 23 to 18 mm Hg and the mean systemic oxygen saturation decreased from 93% to 85%. The mean cardiac index increased from 1.7 to 2.1 L/min/m2 and the mean systemic oxygen transport increased from 268 to 317 ml/min/m2. Complications occurred in 3 patients: transient hypotension during transesophageal echocardiography, a femoral pseudoaneurysm, and a femoral arteriovenous fistula. After septostomy, 6 patients had clinical improvement (resolution of ascites, edema, and no further episodes of syncope); 5 of these 6 patients underwent lung transplantation a mean of 6.1 months after septostomy. Six patients did not have clinical improvement after septostomy. Atrial septostomy improves the hemodynamic status and may be useful as a bridge to lung transplantation in selected patients with pulmonary hypertension.

Graded balloon dilation atrial septostomy in severe primary pulmonary hypertension. A therapeutic alternative for patients nonresponsive to vasodilator treatment

OBJECTIVES

We sought to investigate the acute hemodynamic effects of graded balloon dilation atrial septostomy (BDAS) and to define the long-term impact of this procedure on New York Heart Association functional class and survival in adult patients with primary pulmonary hypertension (PPH).

BACKGROUND

Current treatment strategies for patients with severe and refractory PPH are limited by either technical difficulties and high mortality or cost.

METHODS

We studied 15 patients with severe PPH. BDAS was successfully performed in all patients by crossing the interatrial septum with a Brockenbrough needle, followed by progressive dilation of the orifice with a Mansfield balloon in a hemodynamically controlled, step-by-step manner.

RESULTS

BDAS caused an immediate significant fall in right ventricular end-diastolic pressure and in systemic arterial oxygen saturation and an increase in cardiac index. One patient died, and 14 survived the procedure and significantly improved their mean functional class (from 3.57 +/- 0.6 to 2.07 +/- 0.3 [mean +/- SD], p < 0.001). Exercise endurance (6-min test) also improved from 107 +/- 127 to 217 +/- 108 m (p < 0.001). Because of spontaneous closure, BDAS was repeated in four patients. The survival rate among patients who survived the procedure was 92% at 1, 2 and 3 years, which is better than that for historical control PPH patients (73%, 59% and 52%, respectively).

CONCLUSIONS

With careful monitoring, BDAS is a safe and useful palliative treatment for selected patients with severe PPH.

Balloon atrial septostomy increases cardiac index and may reduce mortality among pulmonary hypertension patients awaiting lung transplantation

The prognosis for patients with pulmonary hypertension is extremely poor. Predictors of poor prognosis among these patients include a cardiac index less than 2.8 L/m/m2, a mean pulmonary artery pressure higher than 50 mm Hg, a mean right atrial pressure more than 10 mm Hg, and PaO2 less than 70 mm Hg. Balloon atrial septostomy was performed as a palliative procedure in six patients with pulmonary hypertension to limit further deterioration while they awaited lung transplantation. The goal of balloon atrial septostomy was to increase cardiac output while limiting the reduction in systemic oxygen saturation to less than 10% of baseline. This procedure may proven to be a valuable adjunct to reduce morbidity and mortality from right ventricular failure for pulmonary hypertension candidates awaiting lung transplantation.

Patient selection, evaluation, and preoperative management for lung transplant candidates

The selection process to assess candidacy for transplant is based on medical and psychosocial criteria and surgical considerations. The degree of disease severity requiring transplantation for survival has become more apparent as the disparity in survival outcome widens between patients with and without transplant. The contraindications to transplant surgery have been modified over time. Candidate selection is considered in the context of the risks and benefits of the surgical procedure on a case by case basis. The wait for transplant has increased as the growth in the number of candidates for transplant exceeds available donors. As much as 30% of patients die on the UNOS waiting list.

Percutaneous balloon dilatation of the atrial septum: immediate and midterm results

OBJECTIVES

To assess the effectiveness of atrial septostomy by percutaneous balloon dilatation in patients with congenital heart defects or primary pulmonary hypertension.

PATIENTS AND DESIGN

Twenty three patients (15 boys, eight girls; aged 10 days to 10 years; 17 with congenital heart defects and six with primary pulmonary hypertension), all haemodynamically unstable under optimal medical treatment, underwent atrial septostomy by percutaneous balloon dilatation.

INTERVENTIONS

The balloon catheter entered the left atrium through a patent foramen ovale (n = 14) or via transseptal puncture in cases with an intact atrial septum (n = 9). The size of the balloons used ranged from 13 to 18 mm.

RESULTS

There were no complications. The interatrial communication (mm) increased (P < 0.05) after dilatation and remained unchanged (P = NS) during a 16.6 (13.8) month follow up (2 (1.7) v 8.8 (1.4) v 8.2 (1.1), respectively). Transatrial gradient (mm Hg) fell and arterial oxygenation (%) improved both in patients with transposition (6.3 (0.8) v 0.8 (1) (P = 0.0001) and 40.6 (4.2) v 76.5 (4.8) (P = 0.0001), respectively) and in those with mitral atresia (13.4 (1.9) v 2 (1.4) (P = 0.0001) and 77.1 (3.9) v 81.5 (4.2) (P = 0.008), respectively). There were two failures, one early and one late, both in the group of patients with mitral atresia or stenosis. A decrease in arterial oxygenation (94.8 (1.5) v 83 (2.4), P = 0.004) and an increase in left atrial pressure (6.8 (0.9) v 8.3 (1.2), P = 0.02) and cardiac index (2.3 (0.2) v 3.1 (0.2) l/min/m2, P = 0.002) was observed in patients with primary pulmonary hypertension.

CONCLUSIONS

Percutaneous balloon dilatation is an effective and safe procedure for creating an adequate interatrial communication that can be used as an alternative to blade septostomy.

Creation of a controlled venoarterial shunt. A surgical intervention for right-side circulatory failure

BACKGROUND

Right-side circulatory failure (RSCF), a common complication of heart transplant and left ventricular assist device recipients, results in decreased cardiac output because of diminished flow across the pulmonary circuit. We hypothesized that creation of a controlled venoarterial shunt would result in decompression of the right ventricle and improved systemic cardiac output at tolerable oxygen saturations.

METHODS AND RESULTS

A venoarterial shunt was created in a large-animal model (calf, n = 6). RSCF was induced by banding the pulmonary artery. Hemodynamic measures and blood gas determinations were obtained during nonshunted and shunted states. Pulmonary artery banding increased mean right ventricular systolic pressure from 44.9 +/- 2.1 mm Hg (mean +/- SEM) to 85.9 +/- 6.9 mm Hg (P < .05, paired t test) and decreased mean aortic flow from 7.8 +/- 1.0 to 4.2 +/- 1.1 L/min (P < .05). Flow through a venoarterial shunt at approximately 40% of cardiac output resulted in a decrease in right ventricular end-systolic pressure from 85.9 +/- 6.9 to 72.1 +/- 5.6 mm Hg (P < .01, ANOVA), a decrease in mean pulmonary artery pressure from 42.9 +/- 5.0 to 37.2 +/- 3.8 mm Hg (P < .01), and an increase in aortic flow from 4.2 +/- .05 to 5.1 L/min (P < .01). Left ventricular stroke work decreased from 2.22 +/- 0.28 to 1.55 +/- 0.88 (P < .05). Carotid artery oxygen saturation did not change significantly (99.9 +/- .02 to 97.6 +/- 1.7) during shunting.

CONCLUSIONS

A controlled venoarterial shunt improved hemodynamics and cardiac output in a large animal model with RSCF. This strategy may be useful in the management of transplant and left ventricular assist device recipients with perioperative RSCF.

Right-to-left veno-arterial shunting for right-sided circulatory failure

BACKGROUND

Right-sided circulatory failure, a complication of heart transplantation and left ventricular assist device use, results in decreased cardiac output due to diminished flow across the pulmonary circuit. We hypothesized that creation of a controlled right-to-left shunt would result in decompression of the right ventricle and improved systemic cardiac output at tolerable oxygen saturations. We also hypothesized that a peripheral veno-arterial shunt is physiologically superior to a central shunt.

METHODS

Right atrial-femoral artery and right atrial-left atrial shunts were created in a large animal model (calf). Right-sided circulatory failure was induced by banding the pulmonary artery. Hemodynamic measures and blood gas determinations were obtained during nonshunted and shunted states.

RESULTS

Peripheral and central shunts resulted in decreased right-sided pressures and increased cardiac output. Arterial oxygen saturation remained greater than 90% during shunting. The peripheral shunt had the added advantage of decreasing left ventricular end-diastolic pressure and left ventricular stroke work.

CONCLUSIONS

A controlled right-to-left shunt improved hemodynamics and cardiac output in a large animal model with right-sided circulatory failure. This strategy may be useful in the management of transplant and left ventricular assist device recipients with perioperative right-sided circulatory failure. Our studies also indicate that creation of a peripheral shunt has both physiologic and technical advantages over a central shunt.