Stent-based approach for ventricle-to-coronary artery bypass

Physiological motion modeling for organ-mounted robots

BACKGROUND

Organ-mounted robots passively compensate heartbeat and respiratory motion. In model-guided procedures, this motion can be a significant source of information that can be used to aid in localization or to add dynamic information to static preoperative maps.

METHODS

Models for estimating periodic motion are proposed for both position and orientation. These models are then tested on animal data and optimal orders are identified. Finally, methods for online identification are demonstrated.

RESULTS

Models using exponential coordinates and Euler-angle parameterizations are as accurate as models using quaternion representations, yet require a quarter fewer parameters. Models which incorporate more than four cardiac or three respiration harmonics are no more accurate. Finally, online methods estimate model parameters as accurately as offline methods within three respiration cycles.

CONCLUSIONS

These methods provide a complete framework for accurately modelling the periodic deformation of points anywhere on the surface of the heart in a closed chest.

Feasibility of dynamic CT-based adenosine stress myocardial perfusion imaging to detect and differentiate ischemic and infarcted myocardium in an large experimental porcine animal model

The purpose of the study is feasibility of dynamic CT perfusion imaging to detect and differentiate ischemic and infarcted myocardium in a large porcine model. 12 Country pigs completed either implantation of a 75 % luminal coronary stenosis in the left anterior descending coronary artery simulating ischemia or balloon-occlusion inducing infarction. Dynamic CT-perfusion imaging (100 kV, 300 mAs), fluorescent microspheres, and histopathology were performed in all models. CT based myocardial blood flow (MBFCT), blood volume (MBVCT) and transit constant (Ktrans), as well as microsphere's based myocardial blood flow (MBFMic) were derived for each myocardial segment. According to histopathology or microsphere measurements, 20 myocardial segments were classified as infarcted and 23 were ischemic (12 and 14 %, respectively). Across all perfusion states, MBFCT strongly predicted MBFMic (β 0.88 ± 0.12, p < 0.0001). MBFCT, MBVCT, and Ktrans were significantly lower in ischemic/infarcted when compared to reference myocardium (all p < 0.01). Relative differences of all CT parameters between affected and non-affected myocardium were higher for infarcted when compared to ischemic segments under rest (48.4 vs. 22.6 % and 46.1 vs. 22.9 % for MBFCT, MBVCT, respectively). Under stress, MBFCT was significantly lower in infarcted than in ischemic myocardium (67.8 ± 26 vs. 88.2 ± 22 ml/100 ml/min, p = 0.002). In a large animal model, CT-derived parameters of myocardial perfusion may enable detection and differentiation of ischemic and infarcted myocardium.

Myocardial CT perfusion imaging in a large animal model: comparison of dynamic versus single-phase acquisitions

OBJECTIVES

This study sought to compare dynamic versus single-phase high-pitch computed tomography (CT) acquisitions for the assessment of myocardial perfusion in a porcine model with adjustable degrees of coronary stenosis.

BACKGROUND

The incremental value of the 2 different approaches to CT-based myocardial perfusion imaging remains unclear.

METHODS

Country pigs received stent implantation in the left anterior descending coronary artery, in which an adjustable narrowing (50% and 75% stenoses) was created using a balloon catheter. All animals underwent CT-based rest and adenosine-stress myocardial perfusion imaging using dynamic and single-phase high-pitch acquisitions at both degrees of stenosis. Fluorescent microspheres served as a reference standard for myocardial blood flow. Segmental CT-based myocardial blood flow (MBFCT) was derived from dynamic acquisitions. Segmental single-phase enhancement (SPE) was recorded from high-pitch, single-phase examinations. MBFCT and SPE were compared between post-stenotic and reference segments, and receiver-operating characteristic curve analysis was performed.

RESULTS

Among 6 animals (28 ± 2 kg), there were significant differences of MBFCT and SPE between post-stenotic and reference segments for all acquisitions at 75% stenosis. By contrast, although for 50% stenosis at rest, MBFCT was lower in post-stenotic than in reference segments (0.65 ± 0.10 ml/g/min vs. 0.75 ± 0.16 ml/g/min, p < 0.05), there was no difference for SPE (128 ± 27 Hounsfield units vs. 137 ± 35 Hounsfield units, p = 0.17), which also did not significantly change under adenosine stress. In receiver-operating characteristic curve analyses, segmental MBFCT showed significantly better performance for ischemia prediction at 75% stenosis and stress (area under the curve: 0.99 vs. 0.89, p < 0.05) as well as for 50% stenosis, regardless of adenosine administration (area under the curve: 0.74 vs. 0.57 and 0.88 vs. 0.61, respectively, both p < 0.05).

CONCLUSIONS

At higher degrees of coronary stenosis, both MBFCT and SPE permit an accurate prediction of segmental myocardial hypoperfusion. However, accuracy of MBFCT is higher than that of SPE at 50% stenosis and can be increased by adenosine stress at both degrees of stenosis.

Coronary venous retroperfusion: an old concept, a new approach

The potential of the coronary veins for revascularization has been evaluated by many investigators for more than a century. The major hurdle has been the damage of veins during sudden exposure to arterial pressure. The solution to this problem has typically involved the use of intricate and complicated apparatus and devices, which has prevented routine clinical utility in the catheterization laboratory. This review examines this old concept from a new perspective and proposes a novel hypothesis to address previous shortcomings. We speculate on an approach that may serve to eliminate the edema and hemorrhage that result during venous retroperfusion as the pressure is suddenly increased to arterial values. We propose the rationale to increase the venous pressure to arterial values more gradually to allow prearterializations of the veins before full exposure of arterial pressure. Finally, we discuss various possible indications for this selective autoretroperfusion strategy to combat myocardial ischemia in cardiogenic shock patients, ST-elevation myocardial infarct patients, no-option patients, and beyond.

Prototype epicardial crawling device for intrapericardial intervention on the beating heart

The development and preliminary testing of a device for facilitating minimally invasive beating-heart intrapericardial interventions are described. We propose the concept of an endoscopic robotic device that adheres to the epicardium by suction and navigates by crawling like an inchworm to any position on the surface under the control of a surgeon. This approach obviates cardiac stabilization, lung deflation, differential lung ventilation, and reinsertion of laparoscopic tools for accessing different treatment sites, thus offering the possibility of reduced trauma to the patient. The device has a working channel through which various tools can be introduced for treatment. The current prototype demonstrated successful prehension, turning, and locomotion on beating hearts in a limited number of trials in a porcine model.

Myocardial blood supply by left ventricle-to-coronary artery channel: an old idea revisited

Coronary artery disease is one of the most important causes of death in Western society. Attempts to revascularize the coronary artery by myocardial retroperfusion, direct revascularization from the left ventricle, and bypass surgery have finally led to percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass grafting (CABG) as standard treatment for coronary artery disease. Direct revascularization from the left ventricle has already been studied in the late 1960s, but the idea was rejected because of a decrease in flow in combination with a failure of myocardial function. Recently, a left ventricle-to-coronary artery (LV-CA) stent has renewed interest as an alternative procedure when PTCA and CABG are no option. Animal studies showed a change in flow pattern from diastolic coronary inflow at baseline to systolic coronary inflow followed by diastolic regurgitive flow during direct ventricular sourcing, resulting in a coronary flow of 50-75% of baseline flow. Global myocardial function decreased in the same extent as the coronary flow suggesting perfusion-contraction matching. In a recent pilot study in the anaesthetized pig, direct revascularization after acute proximal coronary ligation resulted in sufficient blood supply to the outer layers of the myocardium, however, in the inner layers a metabolic disbalance occurred. Incorporation of a valve-like mechanism to minimize the diastolic regurgitive flow may be necessary to improve the performance of the LV-CA stent. In addition, further research should be done in chronic ischemic animal models in which the effect of the collateral circulation on myocardial perfusion and performance is an important issue.

Transmural distribution of myocardial blood perfusion and phasic coronary blood flow pattern in a canine model of acute ischemia

BACKGROUND

Although several investigators have analyzed coronary artery blood flow under various conditions, almost all these studies have measured only some branches of the left anterior descending (LAD), left circumflex (LCX), or right coronary (RCA) artery.

METHODS

In a canine model of acute ischemia (n = 5), we simultaneously assessed (a) regional myocardial blood perfusion using microspheres and (b) phasic coronary blood flow patterns as measured by three epicardial flow probes placed around the LAD, LCX, and RCA.

RESULTS

The results from this study indicated that the LAD supplies blood to the epicardial (r = 0.687, p<0.0001), midwall (r = 0.556, p = 0.0021), and endocardial layers (r = 0.666, p = 0.0001) of the LAD area; the LCX supplies the midwall (r = 0.514, p = 0.0051) and endocardial layer (r = 0.621, p = 0.0004) of the LCX area, antero-lateral papillary muscle (r = 0.548, p = 0.0025), and postero-medial papillary muscle (r = 0.641, p = 0.0002), especially during the diastolic phase; and the RCA supplies the right ventricular apex (r=0.559, p=0.0020), left atrium (r = 0.618, p = 0.0005), right atrium (r = 0.471, p = 0.0114), and postero-medial papillary muscle (r = 0.486, p = 0.0088), especially during the systolic phase.

CONCLUSIONS

These results are potentially relevant to understanding the physiology of myocardial blood perfusion and to improving treatment of acute myocardial ischemia and infarction.

Hemodynamic and vascular effects of ventricular sourcing by stent-based ventricle to coronary artery bypass in patients with multivessel disease undergoing coronary artery bypass surgery

BACKGROUND

The hemodynamic and vascular effects of ventricular sourcing by a stent-based (VSTENT, Percardia) left ventricle-to-coronary artery bypass were studied in a patient subgroup of the European multicenter ADVANTAGE study (ADjunctive treatment with the VCAB/VSTENT myocardial implANT system in coronary Artery bypass Graft patiEnts).

METHODS AND RESULTS

Twelve patients who underwent VSTENT implantation in addition to coronary artery bypass surgery were studied up to 12 months after the procedure. The VSTENT was implanted distal to a hemodynamically relevant coronary artery stenosis. Coronary flow velocity was assessed at rest and during dobutamine stress. Intraoperative VSTENT implantation was successful in 11 of 12 patients. Early postoperative angiograms showed patent VSTENT in 8 of 11 patients, with predominantly systolic flow distal to the VSTENT. Coronary flow velocity reserve induced by dobutamine stress was 1.7+/-0.1 (P=0.006). VSTENT patency at 2- to 6-month follow-up was present in 5 of 11 patients, with concomitant VSTENT stenosis in 4 of those 5. In all patients, coronary flow velocity increased 3- to 4-fold proximal to the VSTENT, which was associated with a moderate degree of arterial remodeling. Except for target vessel reintervention (n=5), no other major adverse events were observed in 11 of 12 patients. One patient died on the second postoperative day, though the cause was probably not related to the VSTENT implantation.

CONCLUSIONS

VSTENT implantation seems to be safe in the mid-term follow-up and leads to a predominantly systolic coronary flow pattern in the vessel supplied by the VSTENT, with a flow reserve similar or close to that seen with conventional bypass. VSTENT patency rate, however, was unacceptably low at 3- to 6-month follow-up and needs to be improved.

Intramyocardial Left Ventricle-to-Coronary Artery Stent: A Novel Approach for the Treatment of Coronary Artery Disease

BACKGROUND

The direct intramyocardial left ventricle-to-coronary artery stent may provide an optional minimally invasive technique for coronary artery bypass graft surgery. We seek to test whether blood flow and regional myocardial function improve with this stent in totally ischemic myocardium.

METHODS

The stent device was implanted in 8 anesthetized dogs using an open chest approach, arteriotomy of the proximal left anterior descending coronary artery, and connection of the vessel to the left ventricular chamber. Regional coronary blood flow and myocardial function were monitored under three conditions: normal coronary flow (baseline), coronary ligation, and stent flow.

RESULTS

Left anterior descending coronary ligation markedly reduced coronary artery blood flow and regional myocardial function. With flow solely from the stent, the blood flow pattern changed to one with high peak forward flow during systole compared with baseline (94.8 +/- 48.9 versus 56.8 +/- 21.1 mL/min; p < 0.05) and one with significant negative backflow during diastole compared with baseline (-37.4 +/- 23.1 versus 11.3 +/- 17.2 mL/min; p < 0.05). However, the resultant mean forward flow increased to approximately 50% of baseline compared with less than 5% of baseline after coronary ligation. Regional myocardial function diminished entirely after coronary ligation, but recovered to approximately 60% of baseline with the stent. Normal systemic hemodynamics and global ventricular contractile function were maintained with the stent.

CONCLUSIONS

The left ventricle-to-coronary artery stent is a simple and readily deployable device that allows the perfusion of epicardial vessels directly from the left ventricle and can provide significant blood flow to improve the performance of ischemic myocardium. It may provide an effective, alternative means of treating coronary artery disease when standard coronary artery bypass graft surgery is not suitable.

Transmural Differences in Myocardial Function and Metabolism During Direct Left Ventricular to Coronary Artery Sourcing

BACKGROUND

We investigated the hypothesis that in the absence of collateral circulation, a left ventricle-coronary artery (LV-CA) bypass will maintain normal LV wall function and metabolism transmurally, both at rest and during stress, when the left anterior descending coronary artery (LAD) is acutely occluded proximally.

METHODS

In 18 anesthetized pigs (74 +/- 7 kg, mean +/- standard deviation), a covered stent was placed transmurally in the lateral wall of the beating LV and connected to the proximal LAD via an arterial graft. Subepicardial and subendocardial segmental shortening as well as interstitial lactate and glucose concentrations were measured regionally by sonomicrometry and microdialysis, respectively.

RESULTS

When the LAD was occluded proximally, direct left ventricular sourcing decreased the net LAD flow to 64 +/- 25% of the native flow (n = 18, all animals). In the subepicardium, systolic shortening (SS) decreased to 87 +/- 18% of baseline (p = 0.124), with the appearance of minor postsystolic shortening (PSS), and minor changes in interstitial lactate and glucose levels. In the subendocardium, in contrast, SS decreased to 54 +/- 20% (p = 0.001). Marked PSS concurred with a sixfold increase in lactate (p = 0.008), and a 65 +/- 31% decrease in glucose (p = 0.003), indicating subendocardial anaerobic metabolism. Stress induced by infusion of dobutamine increased lactate and decreased glucose concentration in the subepicardium to subendocardial levels, indicating transmural anaerobic metabolism.

CONCLUSIONS

In the anesthetized pig, direct sourcing by a LV-CA bypass distal to an acute coronary occlusion resulted in a 36% decrease in net forward coronary flow, subendocardial anaerobic metabolism, and loss of subendocardial contractile function at rest. These adverse effects extended into the subepicardium when the heart was stressed.

Preliminary evaluation of a mobile robotic device for navigation and intervention on the beating heart

This article describes the development and preliminary testing of a mobile robotic device to facilitate minimally invasive beating-heart intrapericardial intervention. The HeartLander robot will be introduced beneath the pericardium via subxiphoid incision, adhere to the epicardium, navigate to any location, and administer therapy under the control of the physician. As compared to current robotic cardiac surgical techniques, this novel paradigm obviates immobilization of the heart and eliminates access limitations. Furthermore, it does not require lung deflation and differential ventilation and thus could enable outpatient cardiac surgery. The current HeartLander prototypes use suction to maintain prehension of the epicardium and wire actuation to perform locomotion. A fiber optic videoscope displays visual feedback to the physician, who controls the device through a joystick interface. The initial prototype demonstrated successful prehension, turning, and locomotion on open-chest, beating-heart porcine models where the pericardium was removed (N = 3). A smaller second-generation prototype with an injection system demonstrated locomotion and myocardial injection of dye, both performed with the pericardium intact (N = 3). These trials illustrate the feasibility of using a miniature mobile robot to navigate upon the beating heart and perform intrapericardial therapy.

Percutaneous approach to a stent-based ventricle to coronary vein bypass (venous VPASS™): comparison to catheter-based selective pressure-regulated retro-infusion of the coronary vein

AIMS

Percutaneous stent-based ventricle-to-coronary vein bypass (venous VPASS) is a new approach to chronic venous arterialization as a treatment modality in an otherwise no option patient with coronary artery disease. In this study, the efficacy of venous VPASS was compared with catheter-based selective pressure-regulated retro-infusion of arterial blood during acute ischaemia.

METHODS AND RESULTS

In seven pigs, venous VPASS was established using a percutaneous ultrasound-guided puncture from the anterior cardiac vein to the left ventricle, with subsequent implantation of an ePTFE-covered stent graft. During left anterior descending artery (LAD) occlusion, coronary venous pressure in the distal anterior cardiac vein increased to 55+/-4 mmHg under conditions of venous VPASS compared with 78+/-5 mmHg during selective pressure-regulated retro-infusion. Significant preservation of regional myocardial function was observed during venous VPASS (67+/-6% baseline) and during selective retro-infusion (83+/-4%) compared with control LAD occlusion (0.4+/-2%).

CONCLUSION

Percutaneous implantation of a PTFE covered stent (venous VPASS) was feasible and associated with significant preservation of regional myocardial function during acute ischaemia in pigs at reasonable levels of mean coronary venous pressure to avoid tissue damage during chronic application.

First Clinical Experience With the VSTENT: A Device for Direct Left Ventricle-to-Coronary Artery Bypass

BACKGROUND

Stent-based left ventricle-to-coronary artery stent (VSTENT) is a newly developed, alternative surgical revascularization procedure (VCAB). We present here our initial experience using this technique.

METHODS

Twelve patients (10 male and 2 female, mean age 61 +/- 13 years) underwent a VCAB concomitant to coronary artery bypass surgery. Myocardial revascularization was performed on-pump with arrested heart in 4 patients, on-pump with beating heart in 6 patients, and off-pump in 2 patients. Average number of coronary anastomoses per patient was 2.4 +/- 0.8. In all cases left internal thoracic artery-to-left anterior descending was used. In each patient only one VSTENT was implanted. Target artery for the VCAB was a diagonal branch in 5 patients, an intermediate branch in one patient and a marginal branch in 6 patients. Mean time for the VCAB was 23 +/- 5 minutes (17 to 30 minutes).

RESULTS

An immediate procedural success was observed in 11 of 12 cases. In one case VCAB was not successful and conventional aortocoronary bypass was performed. One patient died on the second postoperative day due to a systemic inflammatory response syndrome. Autopsy demonstrated a patent VSTENT. Angiography was performed in 10 patients 2 to 16 days (9 +/- 5 days) postoperatively showing a patent VSTENT in 8 patients.

CONCLUSIONS

The VCAB was feasible and potentially safe in the short-term postoperative follow-up, particularly with increasing experience after the first patients. Though the VSTENT is a promising tool for myocardial revascularization, long-term safety, patency, and performance of the device needs to be determined.

New devices for percutaneous coronary intervention are rapidly making bypass surgery obsolete

PURPOSE OF REVIEW

This review summarizes recent and cumulative progress in the success, safety, applicability, and durability of percutaneous coronary intervention.

RECENT FINDINGS

Improvements in basic percutaneous coronary intervention (PCI) equipment and the availability of bare metal stents in the mid-1990s improved acute procedural success to 98%, reduced the emergency surgery rate to 0.2%, and reduced the incidence of recurrent symptoms due to restenosis at the treated site to 15 to 20%. The recent availability of drug-eluting stents has reduced the in-stent neointimal proliferation that causes restenosis and reduced the incidence of symptomatic recurrence to less than 5%, rivaling that of bypass surgery. The work on better antithrombotic pharmacology, distal embolic protection, and devices for crossing chronic total occlusions will further add to the armamentarium for catheter-based revascularization.

SUMMARY

Based on progress over the past decade, PCI has grown to represent about two-thirds of all coronary revascularization (800,000 PCI vs 350,000 bypass surgeries). Recent and ongoing progress will make bypass surgery largely obsolete within the next several years.

Current concepts and applications of coronary venous retroinfusion

Retroinfusion of the coronary veins has gained attention for therapeutic approaches which target drugs, genes or cells to ischemic myocardium. Besides anatomy of the coronary venous system, the pressure flow relationship during retroinfusion and the efficacy of pressure-regulated selective retroinfusion for targeted delivery of drugs is reported. Moreover, we describe adenoviral and liposomal gene transfer into ischemic and nonischemic myocardium, outline studies in chronic ischemic preclinical models treated by retroinfusion of pro-angiogenic agents and discuss the impact of retroinfusion for cell-based regenerative therapy of the diseased myocardium.

Myocardial blood supply through a direct left ventricle–coronary artery shunt is not aided by augmented coronary capacitance

OBJECTIVES

Left ventricle-coronary artery shunting is proposed as an alternative means of myocardial revascularization when standard methods are not an option. During diastole, however, regurgitant coronary flow to the left ventricle decreases the efficacy of the left ventricle-coronary artery shunt. We investigated whether augmented coronary compliance would improve net forward shunt flow.

METHODS

In 11 anesthetized pigs a specially designed stent was placed through the lateral wall of the left ventricle. Through an arterial graft, it was connected to the proximal left anterior descending coronary artery. A blind stump of the right internal thoracic artery (15 cm) was anastomosed to the distal left anterior descending coronary artery to serve as added coronary compliance chamber. Blood flow was measured in the coronary artery just distal from the left ventricle-coronary artery shunt, as well as in the shunt and in the compliance chamber entrance-exit.

RESULTS

The left ventricle-coronary artery shunt decreased the net forward midcoronary flow to 53% +/- 18% (mean +/- SD) of native flow (8 +/- 4 vs 16 +/- 5 mL/min at baseline, P <.01). The augmented compliance did not significantly increase net forward coronary flow (61% +/- 25% of native flow, P <.01 vs baseline and P =.21 vs left ventricle-coronary artery shunt with normal compliance). The increase in systolic forward flow (53 +/- 23 vs 37 +/- 19 mL/min with normal compliance) was accompanied by a similar increase in diastolic regurgitant flow (-26 +/- 20 vs -16 +/- 16 mL/min).

CONCLUSION

In healthy pigs a left ventricle-coronary artery shunt decreased net forward coronary flow to 53% +/- 18% of native flow. Augmentation of coronary artery compliance did not improve shunt performance.

First human experience with stent-based ventricle-to-coronary artery bypass

Stent-based ventricle-to-coronary artery bypass (VSTENT) has been shown experimentally to provide systolic instead of physiological diastolic blood flow directly from the left ventricle to a coronary artery distal to a high-grade stenosis. We report on the first successful surgical implantation of a VSTENT in a patient with coronary artery disease. At 3-month follow-up, the VSTENT was patent and showed sufficient regional blood flow at rest with a significant flow reserve. In addition, the patient was asymptomatic during exercise testing. Though encouraging, these observations have to be confirmed and are the subject of an ongoing multicenter study.