Safety and interaction of patients with implantable cardiac defibrillators driving a hybrid vehicle

BACKGROUND

Electromagnetic interference (EMI) can affect the function of implantable cardioverter defibrillators (ICD). Hybrid electric vehicles (HEV) have increased popularity and are a potential source of EMI. Little is known about the in vivo effects of EMI generated by HEV on ICD.

OBJECTIVE

This study evaluated the in vivo interaction between EMI generated by HEV with ICD.

METHODS AND RESULTS

Thirty patients (73±9 y/o; 80% male) with stable ICD function were exposed to EMI generated by a Toyota Prius Hybrid®. The vehicle was lifted above the ground, allowing safe changes in engine rotation and consequent variations in electromagnetic emission. EMI was measured (NARDA STS® model EHP-50C) and expressed in A/m (magnetic), Volts/m (electrical), and Hertz (frequency). Six positions were evaluated: driver, front passenger, right and left back seats, outside, at the back and front of the car. Each position was evaluated at idle, 30 mph, 60 mph and variable speeds (acceleration-deceleration-brake). All ICD devices were continuously monitored during the study. The levels of EMI generated were low (highest mean levels: 2.09A/m at right back seat at 30 mph; and 3.5V/m at driver seat at variable speeds). No episode of oversensing or inadvertent change in ICD programming was observed.

CONCLUSION

It is safe for patients with ICD to interact with HEV. This is the first study to address this issue using an in vivo model. Further studies are necessary to evaluate the interaction of different models of HEV or electric engine with ICD or unipolar pacemakers.

Autologous Dermal Fibroblast Injections Slow Atrioventricular Conduction and Ventricular Rate in Atrial Fibrillation in Swine

Background—

Nonpharmacological ventricular rate control in atrial fibrillation (AF) without producing atrioventricular (AV) block remains a clinical challenge. We investigated the hypothesis that autologous dermal fibroblast (ADF) injection into the AV nodal area would reduce ventricular response during AF without causing AV block.

Methods and Results—

Fourteen pigs underwent electrophysiology study before, immediately, and 28 days after ≈200 million cultured ADFs (n=8) or saline (n=6) were injected under electroanatomical guidance in the AV nodal area, with continuous 28-day ECG recording. In the ADF group at 28 days postinjection, there were prolongations of PR interval (after versus before: 130±13 versus 113±14 ms, P =0.04), of AH interval during both sinus rhythm (92±13 versus 76.8±8 ms, P <0.01) and atrial pacing at 400 ms (102±13 versus 91±9 ms, P <0.01), and of AV node Wenckebach cycle length (230±19 versus 213±24 ms, P <0.01), with no changes in the control group. The RR interval during induced AF 28 days after injections was 24% longer in ADF-treated group compared with controls (488±120 versus 386±116 ms, P <0.001). Histological analysis revealed presence of ADF-labeled cells in the AV nodal area at 28 days. Transient accelerated junctional rhythm during injections, and transient nocturnal Mobitz I AV conduction occurred early postinjection in both groups.

Conclusions—

Cells survived for 4 weeks and significantly slowed AV conduction and ventricular rate in acutely induced AF. Critically, despite a large number of injections in the AV nodal area and marked effects on AV conduction, AV block did not occur. Further studies are necessary to determine the clinical feasibility and safety of this strategy for ventricular rate control in AF.

Bone marrow-derived B cells preserve ventricular function after acute myocardial infarction

OBJECTIVES

In view of evidence that mature cells play a role in modulating the stem cell niche and thereby stem cell potential and proliferation, we hypothesized that a mature bone marrow (BM) mononuclear cell (MNC) infusion subfraction may have particular potency in promoting hematopoietic or resident stem cell-induced cardiac repair post-infarction.

BACKGROUND

Treatment of acute myocardial infarction (MI) with BM MNC infusion has shown promise for improving patient outcomes. However, clinical data are conflicting, and demonstrate modest improvements. BM MNCs consist of different subpopulations including stem cells, progenitors, and differentiated leukocytes.

METHODS

Stem cells (c-kit+) and subsets of mature cells including myeloid lineage, B and T-cells were isolated from bone marrow harvested from isogeneic donor rats. Recipient rats had baseline echocardiography then coronary artery ligation; 1 x 10(6) cells (enriched subpopulations or combinations of subpopulations of BM MNC) or saline was injected into ischemic and ischemic border zones. Cell subpopulations were either injected fresh or after overnight culture. After 2 weeks, animals underwent follow-up echocardiography. Cardiac tissue was assayed for cardiomyocyte proliferation and apoptosis.

RESULTS

Fractional ventricular diameter shortening was significantly improved compared with saline (38 +/- 3.2%) when B cells alone were injected fresh (44 +/- 3.0%, p = 0.035), or after overnight culture (51 +/- 2.9%, p < 0.001), or after culture with c-kit+ cells (44 +/- 2.4%, p = 0.062). B cells reduced apoptosis at 48 h after injection compared with control cells (5.7 +/- 1.2% vs. 12.6 +/- 2.0%, p = 0.005).

CONCLUSIONS

Intramyocardial injection of B cells into early post-ischemic myocardium preserved cardiac function by cardiomyocyte salvage. Other BM MNC subtypes were either ineffective or suppressed cardioprotection conferred by an enriched B cell population.

Toxic vessel reaction to an absorbable polymer-based paclitaxel-eluting stent in pig coronary arteries

OBJECTIVES

The goal of this study was to evaluate a new drug-eluting stent (DES) comprising a bioabsorbable polymer eluting a moderate dose of paclitaxel in a clinically relevant animal model.

BACKGROUND

Although DES limit restenosis, adverse vascular pathologies and toxicities continue to be of major concern. Optimization of DES components, especially completely absorbable polymers, may reduce these toxicities.

METHODS

Bare-metal (BM), absorbable polymer coating only (POLY), and polymer-based paclitaxel-eluting (PACL) stents were implanted in porcine coronary arteries using intravascular ultrasound (IVUS) to optimize stent apposition. The dose density of paclitaxel was 0.30-0.35 mcg/mm2, with in vitro elution studies demonstrating a gradual elution over 6-8 weeks. The animals were terminated at 1 week, 1 month and 3 months. Histopathologic and histomorphometric analyses were perform.

RESULTS

The arteries with PACL showed extensive smooth muscle cell necrosis at 1 week and poor apposition of stent struts at 1 month (malapposition measured as gap width between strut and internal elastic lamina), with greater gap width compared to the BM and POLY groups (0.22 mm +/- 0.02 vs. 0.03 mm +/- 0.02 and 0.02 mm +/- 0.01, respectively; p < 0.001). At 3 months, the PACL group showed rebound neointimal thickness and histological percent stenosis compared to the BM group (0.48 mm +/- 0.14 vs. 0.07 mm +/- 0.02, respectively; p < 0.001 and 59% +/- 11 vs. 17% +/- 2, respectively; p < 0.001).

CONCLUSIONS

Despite in vitro data showing slow, sustained release of paclitaxel from a bioabsorbable polymer, the porcine coronary artery model demonstrated a sequence of medial necrosis, stent malapposition and late neointimal thickening. Since the therapeutic window for paclitaxel may be narrower than currently inferred, thorough preclinical testing coupled with the polymer development process for stents eluting paclitaxel is needed.

Safety of intramyocardial injection of autologous bone marrow cells to treat myocardial ischemia in pigs

OBJECTIVE

The purpose of this study is to determine the potential adverse consequences of intracardiac injections of bone marrow mononuclear cells (BMCs) to facilitate the revascularization of ischemic myocardium.

BACKGROUND

Bone marrow mononuclear cells are used to treat heart failure, though there are few studies that evaluated the safety of BMC transplantation for chronic myocardial ischemia.

METHODS

The pigs received coronary ameroid constrictors to induce chronic myocardial ischemia and left ventricular dysfunction. At 4 weeks, autologous BMCs were injected intramyocardially by Boston Scientific Stiletto catheter with low-dose (10(7) cells) or high-dose BMC (10(8)). Control animals received saline. Blood samples were collected for hematological and chemical indices, including cardiac enzyme levels at regular time intervals postinfarction. At 7 weeks, animals underwent electrophysiological study to evaluate the arrhythmic potential of transplanted BMC, followed by necropsy and histopathology.

RESULTS

No mortalities were associated with intramyocardial delivery of BMC or saline. At Day 0, the total creatine phosphokinase (CPK) was in the normal range in all groups. All groups had significant elevations in CPK after ameroid placement, with no significant differences between groups. At 7 weeks, CPK in all groups had returned to pretreatment levels. Electrophysiological assessment revealed that one control animal had an inducible arrhythmia. No arrhythmias were induced in low- or high-dose BMC-treated pigs. There were no histopathological changes associated with BMC injection.

CONCLUSION

This study showed, in a clinically relevant large-animal model, that catheter-based intramyocardial injection of autologous BMC into ischemic myocardium is safe.

A clinically relevant large-animal model for evaluation of tissue-engineered cardiac surgical patch materials

Extracellular matrix (ECM) scaffolds may be useful as a tissue engineering approach toward myocardial regeneration in the infarcted heart. An appropriate large-animal model for testing the utility of biologically derived ECM in this application is needed. The purpose of this study was to develop such a model for optimal procedural success during and after patch implantation surgery. Myocardial infarction (MI) was created by embolization of the diagonal artery (DA) branch of the left anterior descending coronary artery with collagen suspension. After 4 to 6 weeks, 14 pigs received patch implant (ECM or expanded polytetrafluoroethylene). Six pigs were infarcted in the first DA and seven pigs in the second DA. Electrophysiology study was performed within 3 days before surgery. During surgery, the size and location of the infarct were measured. Infarcted myocardium (1.5-cm diameter) was transmurally excised under partial cardiopulmonary bypass. Patches (3-cm diameter) were sutured to the endomyocardial defect. Four pigs died postoperatively. After 1 month, 10 pigs were euthanized and the locations of patches were examined. Success rate of patch implant in the second DA (85.7%) was higher than the first DA (50%) group. Infarct size in the second DA was smaller than in the first DA (4.6+/-1.2 vs. 10.8+/-2.4 cm(2), P<.05). The second DA was more anteriorly positioned, which enabled easier access from the midsternal thoracotomy. However, the first DA was more laterally located requiring more manipulation of the heart during surgery. Electrophysiology revealed no ventricular tachyarrhythmia in the second DA but 33.3% in the first DA group (P<.05). At necropsy, the endocardial position of the first DA-infarct patches was anteroapical, whereas the second DA-infarct patches were more basolateral and often involved the anterior papillary muscle. The success rate of patch implant was associated with infarction size and location, and may be related to arrhythmic substrate. Experimental MI created by the second DA embolization is a feasible model for investigation of tissue-engineered cardiac patch implantation. This large-animal model is also suitable for study of cell therapy via endocardial catheter-based approaches or open surgical methods.

Impact of intraaortic balloon counterpulsation on arterial blood flow in juvenile pigs with heart failure

OBJECTIVES

To assess the impact of intraaortic balloon counterpulsation on coronary, renal and aortic blood flow in an animal heart failure model.

BACKGROUND

Heart failure exacerbations are still often treated with inotropic medications despite a lack of evidence demonstrating any benefit with these drugs. Intraaortic balloon counterpulsation may be considered in certain cases a bridge to recovery.

METHODS

Four juvenile pigs underwent pacemaker implantation to induce a rapid-pacing mediated dilated cardiomyopathy. After approximately 4 weeks of rapid pacing, the mean ejection fraction was reduced to 28.8+/-9.5% with a mean systolic blood pressure of 64/44 mmHg. The pigs then underwent surgical placement of flow probes around the circumflex coronary artery, renal artery and infrarenal aorta. A Millar catheter was used to calculate Dp/Dt and a Swan-Ganz to calculate cardiac output. Data were recorded at baseline and after 10 minutes of balloon pumping. The pigs were euthanized post-procedure.

RESULTS

Coronary blood flow was increased 9.7% by balloon counterpulsation from 38.3 +/- 12.0 to 42.0+/-11.4 ml/s (p=NS). Renal blood flow was reduced 11.9% by counterpulsation from 130.0+/-88.6 ml/s to 114.5+/-76.6 ml/s (p=NS). Infrarenal aortic blood flow was not changed (mean of 900 ml/s with and without counterpulsation); blood pressure, cardiac output and Dp/Dt were not changed after 10 minutes of pumping. There was little impact observed by changing the position of the balloon closer to or farther away from the apex of the aortic arch.

CONCLUSION

Intraaortic balloon counterpulsation did not significantly improve hemodynamics in the pig heart failure model. This may be attributed to the high compliance of the juvenile pig's aorta, thus attenuating the pressure wave generated by counterpulsation. A larger volume balloon would merit investigation for this application.

Pulmonary veins isolation to treat patients with refractory paroxysmal atrial fibrillation: clinical results after a single procedure

OBJECTIVE

The purpose of this study was to access the clinical outcome of patients submitted to a single procedure of radiofrequency pulmonary veins (PV) isolation to treat refractory paroxysmal atrial fibrillation (AF).

METHODS

This study included 49 consecutive patients (36 male; mean age 54+/-10 years old) who had frequent symptomatic paroxysmal AF refractory to at least three antiarrhythmic drugs. We used a circular decapolar catheter for mapping PVs - left atrial connections and a 4-mm distal tip catheter for ablation (30 W and 50 C), aiming to achieve electrical isolation of 3 -4 PVs.

RESULTS

Twenty-five patients (51%) did not present any AF recurrence in a mean follow-up of 12+/-5 months. Twenty-four (49%) had at least one recurrence during outcome; twenty (83%) of them within the first month after the procedure and four after two to nine months. After introducing antiarrhythmic drugs 15 (63%) patients were under control, 10 were asymptomatic and five complained of sporadic short duration AF episodes. Nine (37%) patients remained very symptomatic despite the use of antiarrhythmic drugs and were referred to a new procedure of PV isolation. No patient presented major complications. At the end of the follow-up, 35 (71%) patients remained in stable sinus rhythm with no AF recurrences after a single procedure, 50% of them without antiarrhythmic drugs.

CONCLUSION

Most patients who present symptomatic paroxysmal AF refractory to antiarrhythmic drugs obtain a good clinical control after a single PV isolation procedure.

Slow pathway catheter ablation of atrioventricular nodal re-entrant tachycardia guided by electroanatomical mapping: a randomized comparison to the conventional approach

BACKGROUND

Electroanatomical mapping may be expected to improve safety, efficiency and efficacy of selective slow pathway ablation for atrioventricular nodal re-entrant tachycardia (AVNRT). The goal of this prospective randomized study was to compare the efficiency of conventional fluoroscopic and electroanatomical mapping in guiding catheter ablation of AVNRT.

METHODS AND RESULTS

Following induction of typical AVNRT, 20 consecutive patients were randomized to either conventional fluoroscopic or electroanatomical (CARTO) mapping to guide slow pathway ablation using a 4mm electrode. Endpoints for ablation were non-inducibility and no more than a single AV nodal echo on aggressive retesting. Acute procedural success was 100% in both groups, with no complications. Although there were no differences in time taken for pre- and post-ablation electrophysiological evaluations, in the electroanatomical group the ablation portion of the procedure showed a substantial reduction in duration (12.6+/-6.8 vs 35.9+/-18.3 min; P< 0.001) and fluoroscopic exposure (0.7+/-0.5 vs 9.6+/-5.0 min; P< 0.001) compared with the fluoroscopic group, reflected in reduced total procedure time (83.6+/-23.6 vs 114+/-19.3 min; P=0.008) and total fluoroscopic exposure (4.2+/-1.4 vs 15.9+/-6.4 min; P< 0.001). Electroanatomical mapping was associated with a lower number (2.7+/-1.6 vs 5+/-2.8; P=0.018), duration (165.3+/-181.6 vs 341+/-177.7s; P=0.013), and total energy delivery (24.3+/-3.1 vs 28.7+/-4.5 watts; P=0.042) of RF applications. There were no acute or long-term (8.9+/-2.2 month) complications or arrhythmia recurrence in either group.

CONCLUSIONS

While both conventional and non-fluoroscopic electroanatomical mapping are associated with excellent results in guiding ablation of typical AVNRT, the latter offers significantly shorter procedure and fluoroscopy times, improving the efficiency of the procedure and reducing X-ray exposure.

Nonsurgical transthoracic mapping and ablation in a child with incessant ventricular tachycardia

We report the case of an 11-month-old child with incessant ventricular tachycardia who underwent two unsuccessful endocardial ablations with standard catheters and in whom the ventricular tachycardia was interrupted only during transthoracic epicardial catheter ablation. This report outlines the usefulness and safety of this novel approach in pediatric patients before surgery when endocardial ablation fails.