Canine Model of Ischemia-Induced Ventricular Tachycardia.

INTRODUCTION: Despite advances in antiarrhythmia therapies, ventricular tachycardia (VT) is a leading cause of sudden cardiac death. Investigation into the characteristics and new treatments for this arrhythmia is required to improve outcomes and a reproducible model of VT would be useful in these endeavors. We therefore created a canine model of ischemia-induced VT. MATERIALS AND METHODS: A pacing lead was implanted in the right ventricle in canines (n = 13) and the left anterior descending artery was occluded in two locations for 2 h and subsequently released to create an ischemia-reperfusion injury. In the 10 dogs that survived the first 48 h following the initial study, a terminal study was conducted 4-7 d later and VT was induced using premature stimulation or burst pacing through the right ventricle lead. The arrhythmia was terminated using either antitachycardia pacing or a defibrillatory shock. Multiple inductions into sustained VT were attempted. RESULTS: Sustained VT was induced in eight of 10 dogs with an average cycle length of 335 ± 70 bpm. Multiple episodes of VT were induced. Episodes of VT exhibited different electrocardiogram morphologies and cycle lengths in individual animals. CONCLUSIONS: This canine model provides a consistent technique for inducing multiple episodes of sustained VT. It may be useful for investigating VT mechanisms and testing novel therapeutics and treatments for patients with VT.

Antitachycardia pacing at the His bundle is safer than conventional right ventricular antitachycardia pacing in a canine myocardial ischemic injury model.

INTRODUCTION: Antitachycardia pacing (ATP) is used to terminate ventricular tachycardia (VT) by delivering rapid, low energy pacing to the right ventricle (RV). Unfortunately, ATP is not effective against all VT episodes and can result in adverse outcomes, such as VT acceleration and degeneration into ventricular fibrillation (VF). Improving ATP is therefore desirable. Our objective was to compare the efficacy and safety of ATP delivered at the His bundle to traditional ATP. METHODS: Six dogs were anesthetized and pacing leads were implanted in the RV and His bundle. The left anterior descending artery was occluded for 2 h to create an ischemic injury. In a study 4-7 days later, a 128-electrode sock was placed snugly around the ventricles and VT was induced using rapid pacing. ATP was delivered from either the His bundle or RV lead, then attempted at the other location if unsuccessful. Success rates and instances of VT acceleration and degeneration into VF were calculated. RESULTS: We induced 83 runs of VT and attempted ATP 128 times. RV ATP was successful in 36% of attempts; His ATP was successful in 38% of attempts. RV ATP resulted in significantly more adverse outcomes. RV and His ATP induced VT acceleration in 9% and 3% of trains, respectively, and induced degeneration into VF in 5% and 1% of trains, respectively. CONCLUSION: His bundle ATP is safer, but not significantly more effective, than RV ATP.

A canine model of chronic ischemic heart failure.

Preclinical large animal models of chronic heart failure (HF) are crucial to both understanding pathological remodeling and translating fundamental discoveries into novel therapeutics for HF. Canine models of ischemic cardiomyopathy are historically limited by either high early mortality or failure to develop chronic heart failure. Twenty-nine healthy adult dogs (30 ± 4 kg, 15/29 male) underwent thoracotomy followed by one of three types of left anterior descending (LAD) coronary artery ligation procedures: group 1 (n = 4) (simple LAD: proximal and distal LAD ligation); group 2 (n = 14) (simple LAD plus lateral wall including ligation of the distal first diagonal and proximal first obtuse marginal); and group 3 (n = 11) (total LAD devascularization or TLD: simple LAD plus ligation of proximal LAD branches to both the right and left ventricles). Dogs were followed until chronic severe HF developed defined as left ventricular ejection fraction (LVEF) < 40% and NH2-terminal-prohormone B-type natriuretic peptide (NT-proBNP) > 900 pmol/L. Overall early survival (48-h postligation) in 29 dogs was 83% and the survival rate at postligation 5 wk was 69%. Groups 1 and 2 had 100% and 71% early survival, respectively, yet only a 50% success rate of developing chronic HF. Group 3 had excellent survival at postligation 48 h (91%) and a 100% success in the development of chronic ischemic HF. The TLD approach, which limits full LAD and collateral flow to its perfusion bed, provides excellent early survival and reliable development of chronic ischemic HF in canine hearts.NEW & NOTEWORTHY The novel total left anterior descending devascularization (TLD) approach in a canine ischemic heart failure model limits collateral flow in the ischemic zone and provides excellent early survival and repeatable development of chronic ischemic heart failure in the canine heart. This work provides a consistent large animal model for investigating heart failure mechanisms and testing novel therapeutics.

Valvular Cytomegalovirus Endocarditis.

Endocarditis is a rare presentation for cytomegalovirus (CMV) infection. We present the case of a 49-year-old man who underwent mitral and tricuspid valve replacement for valvular CMV endocarditis. The patient's past medical history was significant for human immunodeficiency virus, intravenous drug abuse, and chronic hepatitis B. During his clinical course, he was found to have tricuspid and mitral valve vegetations. After progressive valvular destruction despite antibiotic therapy, he underwent successful mitral and tricuspid valve replacement. Pathologic analysis of the culture-negative valve specimens were found to contain inclusion bodies consistent with CMV, and quantitative serum polymerase chain reaction returned a highly elevated CMV DNA count.

Paraplegia after extensive thoracic and thoracoabdominal aortic aneurysm repair: does critical spinal cord ischemia occur postoperatively?

OBJECTIVE: Spinal cord injury can occur not only during extensive thoracoabdominal aneurysm repair but also postoperatively, causing delayed-onset paraplegia. METHODS: A series of 858 thoracoabdominal aneurysm repairs (June 1990-June 2006) with an overall paraplegia rate of 2.7% was analyzed retrospectively. Serial segmental artery sacrifice was monitored by using somatosensory evoked potentials; segmental arteries were not reimplanted. Of a total of 20 cases of paraplegia, 3 occurred intraoperatively and 7 occurred late postoperatively: these will not be analyzed further. In 10 cases (the paraplegia group) spinal cord injury occurred within 48 hours after thoracoabdominal aneurysm repair, despite intact somatosensory evoked potentials at the end of the procedure. These patients with early postoperative delayed paraplegia were compared with 10 matched control subjects who recovered without spinal cord injury. RESULTS: In the paraplegia group a median of 9 segmental arteries (range, 5-12 segmental arteries) were sacrificed. There were 9 male subjects: median age was 63 years (range, 40-79 years), and 4 of 10 had cerebrospinal fluid drainage. A median of 9 segmental arteries (range, 2-12 segmental arteries) were also sacrificed in the matched recovery group. There were 4 male subjects; median age was 66 years (range, 40-78 years), and 8 of 10 had cerebrospinal fluid drainage. During the first 48 hours postoperatively, there were no significant differences in arterial and mixed venous oxygen saturation, partial arterial O2 and CO2 pressures, body temperature, glucose, hematocrit, or pH. The mean central venous pressures, however, were significantly higher in the paraplegic patients from 1 to 5 hours postoperatively (P = .03). In addition, although absolute mean aortic pressures did not differ between matched pairs postoperatively, when pressures were considered as a percentage of individual antecedent preoperative mean aortic pressure, paraplegic patients had significantly lower values during the first 5 hours postoperatively (P = .03). CONCLUSIONS: This study suggests that paraplegia can result from inadequate postoperative spinal cord perfusion caused by relatively minor differences from control subjects in perfusion parameters. Delayed paraplegia can perhaps be prevented with better hemodynamic and fluid management.

Surgical aspects of congestive heart failure.

Despite tremendous advances in the medical management of congestive heart failure the gold standard for the treatment of end stage congestive heart failure remains cardiac transplantation. The acknowledged critical limitation of sufficient suitable organ donors has resulted in the refinement and development of novel surgical alternatives for the treatment of congestive heart failure. These approaches include the extension of current conventional cardiac operations such as mitral valve repair to the failing ventricle, surgically reconstructing the size and shape of the failing left ventricle in order to optimize geometry and render it a more efficient pump, and partial or complete replacement of the ventricle with a mechanical device. The continued evolution of such therapies is likely to one day have a significant epidemiologic impact on patients suffering from end stage heart failure.

Early and late results of combined carotid endarterectomy and coronary artery bypass versus isolated coronary artery bypass.

OBJECTIVE: Optimal management of patients with combined coronary and carotid artery disease remains controversial. This study analyzed the outcomes between simultaneous carotid endarterectomy (CEA) and coronary artery bypass grafting (CABG) vs. isolated CABG. METHODS: We reviewed the early and late follow-up data of 412 patients who underwent either combined CEA/CABG vs. CABG alone between August 1999 and October 2003. All patients undergoing CEA had at least 80% stenosis of one carotid artery. Data were obtained for pre-, intra-, and early postoperative variables. Late follow-up data (range 1.1 to 69.5 months postoperative, mean 42.4 months, median 42.7 months) included myocardial infarctions (MI), stroke and death. Differences between the two groups were investigated. Univariate and multivariate analysis were carried out to identify predictors of death, MI, and stroke in the entire group. RESULTS: There were 27 patients (6.6%) in the CEA/CABG group and 385 patients in the CABG alone group. There was one patient (3.7%) in the CEA/CABG group who had a perioperative stroke versus six (1.6%) in the CABG group (P=0.38). There were no documented postoperative myocardial infarctions (MI) by EKG and CK-MB criteria in both groups. There were no deaths in the CEA/CABG group versus three in the CABG group (P=1.00). Within the follow-up period, strokes developed in 2 (7.4%) CEA/CABG patients and in 7 (2.3%) CABG patients (P=0.16). Three CEA/CABG patients (11.1%) developed MI versus 19 (6.1%) patients in the CABG group (P=0.40). There were 4 (14.8%) deaths in the CEA/CABG group versus 51 (13.4%) in the CABG group (P=0.77). Freedom from death, stroke, and myocardial infarction was not statistically different between the groups at 60 months (all P>0.05). CONCLUSIONS: The addition of CEA to CABG did not increase short- and long-term morbidity and mortality compared to isolated CABG in our group of patients. Combined CEA/CABG can be performed safely in this high-risk group of patients. Prospective randomized study is needed to further substantiate these findings.

Improved outcome after repair of descending and thoracoabdominal aortic aneurysms using modern adjuncts.

OBJECTIVES: To evaluate current strategies to decrease spinal cord and organ dysfunction in patients undergoing repair of descending and thoracoabdominal aneurysms. METHODS: We reviewed 94 consecutive cases of descending and thoracoabdominal aortic aneurysm repairs to determine the impact of modern adjuncts on postoperative neurologic deficit and mortality. The adjuncts used in these patients included perioperative cerebrospinal fluid drainage, distal aortic perfusion, reattachment of critical intercostal vessels, permissive hypothermia and hypothermic circulatory arrest with antegrade cerebral perfusion. Between December 1999 and March 2005, 24/94 (26%) patients were operated on for thoracoabdominal aortic aneurysm type I, seven (7%) for type II, 25/94 (27%) for type III or type IV, and 38/94 (40%) for descending thoracic aneurysms. Perioperative parameters were collected for all patients, and analyzed retrospectively. RESULTS: Twenty (21%) of the patients required hypothermic circulatory arrest for conduction of the operation. The postoperative rate of paraplegia was 3% (3/94). One patient developed temporary paraparesis. Overall operative mortality was 10% (9/94). This included 12/94 (13%) patients who underwent surgery emergently for ruptured or contained rupture of aortic aneurysm. CONCLUSION: Use of perioperative cerebrospinal fluid drainage, distal aortic perfusion and permissive hypothermia result in a low incidence of spinal cord injury and a low operative mortality.