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Biomedical subjects

Ralph J Damiano

Publications and source records attributed to Ralph J Damiano.

At least 19 recordsLinked to original sources
PubMed2007

Implantable cardioverter-defibrillators improve survival after coronary artery bypass grafting in patients with severely impaired left ventricular function.

OBJECTIVE: Patients with severe left ventricular (LV) dysfunction have a poor long term survival despite complete surgical revascularization. Recent data suggests that the use of Implantable Cardioverter-Defibrillator (ICD) improves survival in patients with severe LV dysfunction. We compared the survival impact of ICD implantation in patients with severe LV dysfunction who underwent CABG. METHODS: Between January 1996 and August 2004, 305 patients with LV ejection fraction (EF) < or = 25% had CABG surgery at our institution. Demographics of patients who had received an ICD (ICD+) in the post -operative period was compared to those without ICD (ICD-). Survival was evaluated by the Kaplan-Meier method. RESULTS: Of the entire group, 35 (11.5%) patients received an ICD with a median of 2 (+/-2) years after CABG. Indication for ICD implantation was clinical evidence of non sustained ventricular tachycardia (NSVT). There were no differences between the 2 groups with respect to age, gender, NYHA classification, number of bypasses, or other co-morbidities. Survival at 1, 3 and 5 years was 88%, 79%, and 67% for the ICD- group compared to 94%, 89% and 83% for the ICD+ group, respectively (figure, p < 0.05). CONCLUSION: Implantation of ICD after CABG confers improved short and long term survival benefit to patients with severe LV dysfunction. Prophylactic ICD implantation in the setting of severe LV dysfunction and CABG surgery should be considered.

Aged↗
PubMed2007

Long-term outcomes in valve replacement surgery for infective endocarditis.

BACKGROUND: Infective endocarditis is associated with a high rate of long-term mortality. Patients with a history of intravenous drug use (IVDU) are at increased risk for infective endocarditis. However, few studies have reported results of surgical treatment on this population. We present 19.5 years of experience with surgically treated patients with infective endocarditis. METHODS: A retrospective study of all cardiac surgeries with a diagnosis of infective endocarditis at a single institution from 1986 to 2005 was performed. Logistic stepwise regression with an end point of operative mortality was done. Variables were age, gender, race, history of drug use, previous valve surgery, and previous valve replacement. Perioperative and outcome variables were compared between IVDU and non-IVDU populations. RESULTS: The IVDU population required surgery at a younger age (39 +/- 9 years versus 54 +/- 15 years; p < 0.001). Overall operative mortality was 12% (41/346). The perioperative complication rate was similar for both groups. When adjusted for age, the two groups had similar long-term survival (p = 0.78). Kaplan-Meier estimator showed that survival at 10 and 15 years was 66% and 54% for IVDU and 56% and 42% for non-IVDU (number at risk, 19, 11, and 61, 28, respectively; p = 0.137). Reoperation for recurrent infective endocarditis was necessary in 9 (17%) of 52 of the IVDU group versus 14 (5%) of 270 of the non-IVDU group (p = 0.03). CONCLUSIONS: Patients with a history of IVDU required reoperation for recurrent infective endocarditis at a significantly higher rate than the non-IVDU patients. Long-term survival was similar between the younger IVDU population and the older non-IVDU population. Anticipated life span is one of many factors when considering prosthetic valve choice in this population.

Adult↗
PubMed2006

Spatial and temporal stability of the dominant frequency of activation in human atrial fibrillation.

PURPOSE: Intraoperative activation sequence mapping during atrial fibrillation (AF) is difficult because of the complexity of the data. The data analysis is time consuming, and picking activation times can be ambiguous. The purpose of this study was to determine whether mapping in the frequency domain during AF can be used to rapidly locate the region and assess the stability of the dominant frequency. METHODS: In 33 patients, epicardial bipolar electrograms were intraoperatively recorded from 250 sites during AF. For each electrogram, a power spectrum was calculated using a fast Fourier transform. The peak frequency below 11 Hz was determined from the power spectrum for each electrogram. RESULTS: Isofrequency mapping demonstrated that 91% of the patients exhibited a distinct region of maximum (dominant) frequency at least once during the recording period. Nine percent had no distinct region of dominant frequency. A distinct region of stable dominant frequency was located in the left atrium 30% of the time and the right atrium 12% of the time for the entire recording period. The location of dominant frequency changed during the recording period in 48% of the patients. The dominant frequency was highest in patients with chronic AF (8.29 +/- 1.0 Hz) compared to those with paroxysmal AF (PAF) (6.54 +/- 0.62 Hz, P = .001). The dispersion of frequency was higher in the patients with persistent AF (1.03 +/- 0.4 Hz) than in those with PAF (0.6 +/- 0.3 Hz, P < .001). CONCLUSION: Frequency mapping rapidly and accurately identifies the region of dominant activation frequency. The frequency is faster and more variable in persistent AF than in PAF. The location of the dominant frequency was unstable, changing during the recording period, in half the patients. The location of the dominant frequency was independent of the type of AF.

Action Potentials↗
PubMed2006

Surgical and minimally invasive ablation for atrial fibrillation.

The Cox-Maze procedure, first introduced in 1987, has been the gold standard for the surgical treatment of atrial fibrillation. At 10 years, over 90% of patients remain free from atrial fibrillation. The procedure has been shown to be effective at eliminating the incidence of late stroke in this high-risk population. The development of new ablation technologies has greatly simplified and shortened the Cox-Maze procedure without sacrificing efficacy. These technologies have spurred interest in the development of new, simpler operations for the surgical treatment of atrial fibrillation that can be performed through minimal access and, in some instances, off of cardiopulmonary bypass. The early results with these more limited procedures on the whole have not been as good as with the Cox-Maze procedure, but they are promising. There are many problems with the development of a truly minimally invasive procedure with high efficacy. When patients are referred for surgery, there is no information available regarding the mechanisms of their atrial fibrillation. Thus, it is impossible to tailor the ablation to the individual patient. Future progress will require better understanding of the mechanisms of atrial fibrillation, and the development and refinement of clinical diagnostic technology that will allow for better preoperative diagnosis.

Journal Article↗
PubMed2006

Use of an apical heart suction device for exposure in lung transplantation.

Cardiopulmonary bypass is not necessary for the performance of bilateral sequential lung transplantation in most circumstances. Inadequate exposure to the left hilum is occasionally the sole indication for institution of cardiopulmonary bypass. We report the use of a suction heart positioning device to allow lifting of the heart for improvement of left hilar exposure. This technique has decreased the need for cardiopulmonary bypass when bypass is indicated due to difficult operative exposure.

Equipment Design↗
PubMed2006

Role of the sarcolemmal adenosine triphosphate-sensitive potassium channel in hyperkalemic cardioplegia-induced myocyte swelling and reduced contractility.

BACKGROUND: Hyperkalemic cardioplegia (Plegisol) has been shown to result in myocyte swelling and reduced contractility. We have demonstrated the elimination of these detrimental effects by the addition of an adenosine triphosphate-sensitive K+ (KATP) channel opener. To examine whether the mitochondrial or sarcolemmal KATP channel might be involved, volume and contractility in isolated myocytes from wild-type mice and mice lacking the sarcolemmal KATP channel (Kir6.2-/-) were evaluated. METHODS: Myocytes were perfused for 20 minutes each with control 37 degrees C Tyrode's solution, test solution, and then control solution. Test solutions were (n = 10 per group) either 9 degrees C Plegisol or 9 degrees C Plegisol with 100 micromol/L of diazoxide, a putative mitochondrial-specific KATP channel opener. Cell volume and contractility were measured by digital video microscopy at baseline and during the test solution and reexposure periods. RESULTS: Myocytes from wild-type mice, perfused with 9 degrees C Plegisol, demonstrated significant cell swelling (11.2% +/- 0.4%; p < 0.01) and diminished contractility (32.5% +/- 9.6% reduction in percent shortening, 47.2% +/- 10.1% reduction in peak velocity of shortening, and 52.0% +/- 8.8% reduction in peak velocity of relengthening; p < 0.05) versus baseline. Cell swelling and diminished contractility were significantly reduced by the addition of diazoxide. In Kir6.2-/- myocytes, Plegisol caused a greatly reduced level of cell swelling (3.2% +/- 0.1%; p < 0.01), and this was unaffected by diazoxide. Contractility was unchanged in Kir6.2-/- myocytes after Plegisol. CONCLUSIONS: The sarcolemmal KATP channel appears necessary for exaggerated cell swelling and reduced contractility to occur after hyperkalemic cardioplegia in mouse myocytes.

Animals↗
PubMed2006

Hyperkalemic cardioplegia-induced myocyte swelling and contractile dysfunction: prevention by diazoxide.

BACKGROUND: Hyperkalemic cardioplegia (9 degrees C) results in significant myocyte swelling and reduced contractility, representing a possible mechanism of myocardial stunning. Adenosine triphosphate-sensitive potassium channel (KATP) openers have been shown to ameliorate stunning. This study evaluated the hypothesis that a KATP opener would prevent hyperkalemic cardioplegia-induced myocyte swelling and reduced contractility. METHODS: Isolated rabbit myocytes were perfused with 37 degrees C Tyrode's solution for 20 minutes, followed by test solution (9 degrees C or 37 degrees C) including control Tyrode's, Tyrode's + 100 micromol/L diazoxide (KATP opener), St. Thomas's solution; or 9 degrees C St. Thomas's + 100 micromol/L diazoxide or St. Thomas's + 100 micromol/L diazoxide + 20 micromol/L HMR1098 or 50 micromol/L 5-hydroxydeconoate (KATP blockers) for 20 minutes (n = 8 per group). Myocytes were then reexposed to 37 degrees C Tyrode's solution for 20 minutes. Volume and contractility were measured by videomicroscopy and video-based edge detection, respectively. RESULTS: St. Thomas's solution (9 degrees C) caused significant myocyte swelling and associated reduced contractility (p < 0.05). The addition of diazoxide abolished myocyte swelling (p < 0.0001), and eliminated the associated reduced contractility (p < 0.05). Findings were unchanged by the addition of HMR 1098 and 5-hydroxydeconoate. CONCLUSIONS: Diazoxide prevented myocyte swelling and reduced contractility secondary to hyperkalemic cardioplegia, and this was unchanged by the addition of either KATP channel blocker. Prevention of myocyte swelling was associated with improved contractility, consistent with the hypothesis that myocyte swelling may be a mechanism of myocardial stunning. Diazoxide may play a role in myocyte volume homeostasis by means of a mechanism separate from opening the KATP channel.

Animals↗
PubMed2006

Microwave ablation for atrial fibrillation: dose-response curves in the cardioplegia-arrested and beating heart.

BACKGROUND: Microwave ablation has been used to replace the traditional incisions used in the surgical treatment of atrial fibrillation. However, dose-response curves have not been established in surgically relevant models. The purpose of this study was to develop dose-response curves for the Flex 10 (Guidant, Inc) microwave device in both the acute cardioplegia-arrested heart and on the beating heart. METHODS: Twelve domestic pigs (40 to 45 kg) were subjected to microwave ablation in either the arrested (n = 6) or beating heart (n = 6). The cardioplegia-arrested heart was maintained at 10 degrees to 15 degrees C while six atrial endocardial and seven right ventricular epicardial lesions were created in each animal. On the beating heart, six right atrial and seven ventricular epicardial lesions were created. Ablations were performed for 15, 30, 45, 60, 90, 120, and 150 seconds (65 W, 2.45 GHz). The tissue was stained with 2,3,5-triphenyl-tetrazolium chloride, and sectioned at 5-mm intervals. Lesion depth and width were determined from digital micrographs. RESULTS: Mean atrial wall thickness was 2.8 mm (range, 1 to 8 mm). In the arrested heart, 94% of atrial lesions were transmural at 45 seconds and 100% were transmural at 90 seconds. In the beating heart, only 20% of atrial lesions were transmural despite prolonged ablation times (90 seconds). Ventricular lesion width and depth increased with duration of application, and were similar on the arrested and beating hearts. CONCLUSIONS: Microwave ablation produces linear dose-response curves. Transmural lesions can be reliably produced on the arrested heart, but not consistently on the beating heart.

Acute Disease↗
PubMed2006

Prosthesis-patient mismatch after aortic valve replacement: impact of age and body size on late survival.

BACKGROUND: The purpose of this study was to identify patient subgroups in which prosthesis-patient mismatch most influenced late survival. METHODS: Over a 12-year period, 1,400 consecutive patients underwent bioprosthetic (933 patients) or mechanical (467) aortic valve replacement. Prosthesis-patient mismatch was defined as prosthetic effective orifice area/body surface area less than 0.75 cm2/m2 and was present with 11% mechanical and 51% bioprosthetic valves. RESULTS: With bioprosthetic valves, prosthesis-patient mismatch was associated with impaired survival for patients less than 60 years old (10-year: 68% +/- 7% mismatch versus 75% +/- 7% no mismatch, p < 0.02) but not older patients (p = 0.47). Similarly, with mechanical valves, prosthesis-patient mismatch was associated with impaired survival for patients less than 60 years old (10-year: 62% +/- 11% versus 79% +/- 4%, p < 0.005) but not older patients (p = 0.26). For small patients (body surface area less than 1.7 m2), prosthesis-patient mismatch did not impact survival with bioprosthetic (p = 0.32) or mechanical (p = 0.71) valves. For average-size patients (body surface area 1.7 to 2.1 m2), prosthesis-patient mismatch was associated with impaired survival with both bioprosthetic (p < 0.05) and mechanical (p < 0.005) valves. For large patients (body surface area greater than 2.1 m2), prosthesis-patient mismatch was associated with impaired survival with mechanical (p < 0.04) but not bioprosthetic (p = 0.40) valves. CONCLUSIONS: Prosthesis-patient mismatch had a negative impact on survival for young patients, but its impact on older patients was minimal. In addition, although prosthesis-patient mismatch was not important in small patients, prosthesis-patient mismatch negatively impacted survival for average-size patients and for large patients with mechanical valves.

Adult↗
PubMed2006

Elective surgery for thoracic aortic aneurysms: late functional status and quality of life.

BACKGROUND: Elective surgical treatment for thoracic aortic aneurysms is unique in that it is often performed on asymptomatic patients. Although it has been found to improve survival, the impact of elective surgery on late functional status and quality of life have yet to be examined. METHODS: Over a 5-year period, 110 asymptomatic patients underwent elective thoracic aortic replacement for ascending, descending, or thoracoabdominal aneurysms. Mean age was 67 +/- 9 years (53 > or = 70 years). Functional status, physical and psychological quality of life (Medical Outcome Study 36-Item Short Form Health Survey, in which 50 represents normalized age-matched US population), and survival (Kaplan-Meier) were assessed. RESULTS: Return to normal activity level was independent of age (p > 0.59) and procedure (p > 0.18). At 35 +/- 20 months, psychological quality of life was similar between surgical groups (p > 0.71), but physical quality of life was lower after thoracoabdominal versus ascending or descending aneurysms (p < 0.02). Age did not impact physical quality of life (40 +/- 13 > or = 70 years versus 42 +/- 11 < 70 years, p > 0.58), but older patients had improved psychological quality of life (52 +/- 9 > or = 70 years versus 47 +/- 8 < 70 years, p > 0.03). Overall survival was 79% +/- 4% at 2 years and 70% +/- 5% at 4 years, but was lower with thoracoabdominal versus ascending or descending aneurysms (p < 0.002). Multivariate analysis identified thoracoabdominal (p < 0.004), advanced age (p < 0.03), chronic renal failure (p < 0.03), and congestive heart failure (p < 0.001) as predictors of late death. CONCLUSIONS: Advanced age did not impair return to normal functional status, and older patients had improved psychological quality of life. Survival and physical quality of life were lowest with thoracoabdominal versus ascending or descending aneurysms. Thus, patients with asymptomatic thoracic aneurysms should not be denied elective replacement based on age alone, as functional recovery was not significantly impaired.

Aged↗
PubMed2006

Epicardial microwave ablation on the beating heart for atrial fibrillation: the dependency of lesion depth on cardiac output.

BACKGROUND: Microwave energy is commonly used on the beating heart to create lesions for the surgical treatment of atrial fibrillation. However, lesion transmurality is likely to depend on several factors including tissue thickness and blood flow. This study was designed to determine the effect of cavitary blood flow on transmurality of acute atrial lesions with the FLEX 10 (Guidant Corporation, Santa Clara, Calif) microwave device. METHODS: Six pigs underwent median sternotomy and were placed on cardiopulmonary bypass. Microwave lesions on the atrium were performed for 60 seconds at 65 Watts at 4 different levels of cardiac output by varying cardiopulmonary bypass flow rates. Cardiac output was measured with a pulmonary artery flow probe. Four additional lesions on 2 animals were done for 120 seconds at 65 Watts with 0.0 to 0.5 L/min cardiac output. The animals were sacrificed, and tissue was stained with 2,3,5-triphenyltetrazolium chloride and sectioned at 5-mm intervals. Lesion depth and width were determined from photomicrographs. RESULTS: Sixty-second lesions were transmural in 90%, 65%, 54%, and 46% of atrial sections at cardiac output of 0.0 to 0.5 L/min, 0.6 to 1.9 L/min, 2.0 to 3.9 L/min, and 4.0 L/min or greater, respectively (P < .001). When ablations were performed for 120 seconds with a cardiac output of 0.0 to 0.5 L/min, 100% of lesions were transmural. Lesion width was also related to cardiac output, with the widest lesions produced when cardiac output was 0.0 to 0.5 L/min. CONCLUSIONS: Acute microwave ablation lesion depth and width are strongly dependent on the magnitude of cardiac output. Transmural lesions can be reliably produced on the porcine heart only while on cardiopulmonary bypass.

Animals↗
PubMed2006

Efficacy and safety of right and left atrial ablations on the beating heart with irrigated bipolar radiofrequency energy: a long-term animal study.

OBJECTIVE: The Cox maze procedure is the most effective surgical treatment for atrial fibrillation; however, its complexity has limited its clinical utility. The purpose of this study was to simplify the procedure by using an irrigated bipolar radiofrequency ablation device on the beating heart without cardiopulmonary bypass. METHODS: Six domestic pigs underwent median sternotomy. The pulmonary veins were circumferentially ablated. Electrical isolation was confirmed by pacing. Eight lesions were performed epicardially, and three lesions were performed through purse-string sutures with one of the jaws of the device introduced into the right atrium. After 30 days, magnetic resonance imaging was performed to assess atrial function, pulmonary vein anatomy, and coronary artery patency. Cholinergic stimulation and burst pacing were administered to induce atrial fibrillation. Histologic assessment of the heart was performed after the animal was killed. RESULTS: A modified Cox maze procedure was successfully performed with the irrigated bipolar radiofrequency device with no deaths. In every instance, the pulmonary veins were electrically isolated. Cholinergic stimulation with burst pacing failed to produce atrial fibrillation. Imaging studies revealed tricuspid regurgitation without evidence of pulmonary vein stenosis, coronary artery stenosis, or intra-atrial thrombus. Total atrial ejection fraction was 16.9% +/- 7.5%, a significant reduction. Histologically, 99% of the lesions were transmural, and there was no evidence of coronary sinus injury. CONCLUSION: Lesions on both the right and left atria can be created successfully on the beating heart with irrigated bipolar radiofrequency. The great majority of lesions with this device were transmural. This device should not be used on valvular tissue.

Animals↗
PubMed2006

A new era in the surgical treatment of atrial fibrillation: the impact of ablation technology and lesion set on procedural efficacy.

BACKGROUND/OBJECTIVE: While the Cox-Maze procedure remains the gold standard for the surgical treatment of atrial fibrillation (AF), the use of ablation technology has revolutionized the field. To simplify the procedure, our group has replaced most of the incisions with bipolar radiofrequency ablation lines. The purpose of this study was to examine results using bipolar radiofrequency in 130 patients undergoing a full Cox-Maze procedure, a limited Cox-Maze procedure, or pulmonary vein isolation alone. METHODS: A retrospective review was performed of patients who underwent a Cox-Maze procedure (n = 100), utilizing bipolar radiofrequency ablation, a limited Cox-Maze procedure (n = 7), or pulmonary vein isolation alone (n = 23). Follow-up was available on 129 of 130 patients (99%). RESULTS: Pulmonary vein isolation was confirmed by intraoperative pacing in all patients. Cross-clamp time in the lone Cox-Maze procedure patients was 44 +/- 21 minutes, and 104 +/- 42 minutes for the Cox-Maze procedure with a concomitant procedure, which was shortened considerably from our traditional cut-and-sew Cox-Maze procedure times (P < 0.05). There were 4 postoperative deaths in the Cox-Maze procedure group and 1 in the pulmonary vein isolation group. The mean follow-up was 13 +/- 10, 23 +/- 15, and 9 +/- 10 months for the Cox-Maze IV, the pulmonary vein isolation, and the limited Cox-Maze procedure groups, respectively. At last follow-up, freedom from AF was 90% (85 of 94), 86% (6 of 7), and 59% (10 of 17) in the in the Cox-Maze procedure group, limited Cox-Maze procedure group, and pulmonary vein isolation alone group, respectively. CONCLUSIONS: The use of bipolar radiofrequency ablation to replace Cox-Maze incisions was safe and effective at controlling AF. Pulmonary vein isolation alone was much less effective, and should be used cautiously in this population.

Atrial Fibrillation↗
PubMed2006

Management of arterial injuries caused by laser extraction of indwelling venous pacemaker and defibrillator leads.

The use of laser technology for the removal of pacemaker and defibrillator leads has decreased the lead extraction time and improved the success rate for complete lead removal when compared to traditional techniques. However, this extraction method may be associated with significant complications. This report documents two cases of iatrogenic arteriovenous fistula created by laser lead extraction. Endovascular repair of these fistulas provides an effective and less invasive alternative to open repair.

Aged↗
PubMed2006

Laser assistance for extraction of chronically implanted endocardial leads: infectious versus noninfectious indications.

BACKGROUND: Powered sheaths, including Excimer laser sheaths, were introduced for the removal of transvenous pacing and defibrillator leads. The purpose of this study was to develop an algorithm to better predict which patients are likely to benefit from these devices. METHODS: We reviewed 283 consecutive patients in whom a total of 500 leads (302 pacing and 198 defibrillator leads) were extracted over a 5-year period at our operative facilities. Laser assist was utilized whenever moderate traction failed. RESULTS: In 128 patients, 203 leads were removed for noninfectious indication. In 155 patients, 297 leads for infectious indications, including sepsis 22% (111), pocket infection 23% (115), and erosion 14% (71). Laser assistance was required for 6%+/- 5% (+/- 95% confidence interval) of septic leads, 51%+/- 7% of leads associated with erosion or pocket infection and 60%+/- 7% of noninfected leads (P = 0.001). Laser assistance was necessary more often for leads implanted >12 months (53%+/- 5%) than 12 months or less (6%+/- 5%) (P = 0.001) and for ventricular (52%+/- 6%) compared to atrial (35%+/- 7%) leads (P = 0.001). CONCLUSIONS: Chronically implanted leads (>12 months), especially noninfected leads and leads associated with erosion or pocket infection, should be referred for extraction with powered sheaths to ensure successful removal. However, leads that are associated with systemic sepsis can generally be removed without powered sheaths.

Adolescent↗
PubMed2005

Myocyte volume and function in response to osmotic stress: observations in the presence of an adenosine triphosphate-sensitive potassium channel opener.

BACKGROUND: Hypothermic hyperkalemic cardioplegia results in significant myocyte swelling and impaired contractility. These detrimental effects may be eliminated by the addition of an adenosine triphosphate-sensitive potassium (KATP) channel opener. This study evaluated the hypothesis that a KATP channel opener (diazoxide) would benefit volume homeostasis by limiting volume and subsequent contractility changes during osmotic stress. METHODS AND RESULTS: Isolated rabbit ventricular myocyte volume and contractility were evaluated using video microscopy and field stimulation after exposure to osmotic stress at 37 degrees C. Myocytes were exposed to Tyrode's physiological solution for 20 minutes and test solution for 20 minutes, and then reexposed to Tyrode's for 20 minutes. Test solutions included control Tyrode's (1T) and osmotically altered Tyrode's (2.6T, 0.9T, and 0.6T) solutions with or without the KATP channel opener diazoxide. Severe osmotic stress (2.6T and 0.6T) resulted in significant cell shrinkage and swelling, respectively. This was unchanged by the addition of diazoxide. Mild hyposmotic stress (0.9T) resulted in significant cell swelling that was eliminated by the addition of diazoxide. Cell swelling was associated with reduced contractility. CONCLUSIONS: Cell swelling, but not shrinkage, was detrimental to myocyte contractility. Diazoxide eliminated volume change due to mild hyposmotic stress, similar to that previously noted with hyperkalemic cardioplegia, but did not alter volume change secondary to severe osmotic stress.

Adenosine Triphosphate↗
PubMed2005

Importance of geometry and refractory period in sustaining atrial fibrillation: testing the critical mass hypothesis.

BACKGROUND: The critical mass hypothesis for atrial fibrillation (AF) was proposed in 1914. There has never been a systematic investigation defining the relationship between tissue geometry and AF. The purpose of this study was to determine the association among the probability of maintaining AF and the width, area, weight, effective refractory period (ERP), and wavelength in atrial tissue. METHODS AND RESULTS: Isolated canine atria (n=20) were perfused with Krebs-Henseleit solution. Baseline ERPs were obtained with and without acetylcholine (10E-3.5 mol/L) using single extra-stimulus pacing while unipolar electrograms were recorded from 250 sites. The tissue was then partitioned using bipolar radiofrequency ablation, and the ERPs were measured again with and without acetylcholine. Any section of tissue that maintained AF was divided until the arrhythmia was no longer inducible. ERPs and conduction velocities were measured in all of the sections after each ablation, and the wavelengths were calculated. The probability of AF was found to be correlated with increasing tissue areas, widths, and weights (P<0.001). The probability of AF was significantly associated with the length of the ERP and the wavelength (P<0.001). With shorter ERPs and shorter wavelengths, there was an increased probability of sustained AF. CONCLUSIONS: The probability of sustained AF was significantly associated with increasing tissue area, width, and weight and decreasing ERPs and wavelengths. These data may lead to a better understanding of the mechanism of AF and, thus, help to design more-effective interventional procedures in the future.

Acetylcholine↗