Search PubMed⌕ Search

Biomedical subjects

T D Ivey

Publications and source records attributed to T D Ivey.

At least 37 records · Page 2Linked to original sources
PubMed1988

The use of autologous pericardium for ventricular aneurysm closure.

Closure of the ventriculotomy following ventricular aneurysm resection usually requires buttressing material to provide strength and hemostasis. Although Teflon felt has usually been used, this material is bulky, noncompliant, and prone to infection. Autologous pericardium appears to offer an ideal substitute without the disadvantages of artificial material. A simple technique is described to apply pericardial tissue as a natural buttressing agent for ventriculotomy closure.

Heart Aneurysm↗
PubMed1988

Experimental validation of Doppler echocardiographic measurement of volume flow through the stenotic aortic valve.

In aortic stenosis, evaluation of aortic valve area by the continuity equation assumes that the volume of flow through the stenotic valve can be measured accurately in the left ventricular outflow tract. To test the accuracy of Doppler volume-flow measurement proximal to a stenotic valve, we developed an open-chest canine model in which the native leaflets were sutured together to create variable degrees of acute aortic stenosis. Left ventricular and aortic pressures were measured with micromanometer-tipped catheters. Volume flow was controlled and varied by directing systemic venous return through a calibrated roller pump and back to the right atrium. Because transaortic volume flow will not equal roller pump output when there is coexisting aortic insufficiency (present in 67% of studies), transaortic flow was measured by electromagnetic flowmeter with the flow probe placed around the proximal descending thoracic aorta, just beyond the ligated arch vessels. In 12 adult, mongrel dogs (mean weight, 25 kg), the mean transaortic pressure gradient ranged from 2 to 74 mm Hg, and transaortic volume flow ranged from 0.9 to 3.2 l/min. In four dogs, electromagnetic flow that was measured distal to the valve was accurate compared with volume flow determined by timed collection of total aortic flow into a graduated cylinder (n = 24, r = 0.97, electromagnetic flow = 0.87 Direct +0.13 l/min). In eight subsequent dogs, electromagnetic flow was compared with transaortic cardiac output measured by Doppler echocardiography in the left ventricular outflow tract as circular cross-sectional area [pi(D/2)2] x left ventricular outflow tract velocity-time integral x heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Catheter-mediated electrical ablation: the relation between current and pulse width on voltage breakdown and shock-wave generation.

Voltage waveform breakdown is characteristic of barotraumatic shock-wave generation during electrical catheter ablation of cardiac arrhythmias. The purpose of this investigation was to avoid barotrauma by defining, in vitro, the limits of pulse amplitude and pulse width for rectangular constant-current pulses that do not result in voltage breakdown and subsequently to determine what pulsing frequency is safe for use when high-energy trains of pulses are used. Electric pulses were delivered with a variable waveform modulator with a wide dynamic range and bandwidth capable of delivering pulses of 30-10,000-mu sec duration with amplitudes of up to 25 A. Cathodal pulses were delivered to a 6F catheter immersed in fresh anticoagulated bovine blood warmed to 37 degrees C to stimulate the milieu of a catheter in the chambers of the human heart. The maximum pulse amplitude that could be delivered without incurring voltage waveform breakdown varied inversely with pulse duration. Pulses of 30 mu sec broke down at currents above 24 A (2,500 V). Pulses of 10,000-mu sec duration broke down at 1 A (250 V). The maximum safely delivered energy for a single pulse was 2.5 J for pulses of 80-120 mu sec. Peak power for single pulses was maximum at 50-55 kW with 30-50-mu sec pulses. Charge delivery for single pulses was maximized at 9 mC with long, 10,000-mu sec duration pulses. To deliver an electrical pulse with energy significantly greater than 2.5 J without incurring voltage breakdown, trains of pulses were delivered where each pulse in the train had previously been shown to be free of voltage breakdown.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Ischemic myocardial protection. Comparison of nonoxygenated crystalloid, oxygenated crystalloid, and oxygenated fluorocarbon cardioplegic solutions.

This study was designed to compare myocardial protection with a nonoxygenated crystalloid solution, an oxygenated crystalloid solution, and an oxygenated fluorocarbon cardioplegic solution. Postischemic ventricular performance was studied in three equal (N = 7) groups of dogs subjected to 120 minutes of global ischemia induced at an average myocardial temperature of 18.5 degrees +/- 1.4 degrees C (range 17.0 degrees to 21.0 degrees C). Left ventricular global and regional function was evaluated by sonomicrometry and micromanometers before ischemia and at 45 and 60 minutes after ischemia. Stroke volume index, left ventricular pressure-minor external diameter loop area, percent shortening, first derivative of left ventricular pressure, mean velocity of circumferential fiber shortening, and the slope of the end-systolic pressure were used to evaluate myocardial contractility. In vitro oxygen content of the three cardioplegic solutions was measured at a mean injection temperature of 8.3 degrees +/- 0.6 degrees C: 0.8 +/- 0.1 vol% (nonoxygenated crystalloid cardioplegia), 3.2 +/- 0.2 vol% (oxygenated crystalloid cardioplegia), and 6.2 +/- 0.2 vol% (oxygenated fluorocarbon cardioplegia). Recovery of global and regional function was significantly (p less than 0.05) better with both oxygenated solutions than with the nonoxygenated solution. Differences between the oxygenated crystalloid and fluorocarbon groups were not significant. We conclude: (1) Compared to nonoxygenated crystalloid cardioplegia, oxygenated crystalloid and oxygenated fluorocarbon cardioplegic solutions gave superior myocardial protection during 2 hours of ischemic arrest; (2) no difference was found in protective effects between an oxygenated crystalloid and an oxygenated fluorocarbon solution.

Animals↗
PubMed1987

Intraoperative comparison of sequential-pulse and single-pulse defibrillation in candidates for automatic implantable defibrillators.

Sixteen survivors of cardiac arrest underwent intraoperative comparison of the effectiveness of sequential-pulse and single-pulse defibrillation. Defibrillation was tested alternately with the single-pulse or sequential-pulse technique 10 seconds into an episode of ventricular fibrillation that was induced with alternating current. The sequential-pulse defibrillation technique using truncated exponential pulses was performed with a right ventricular endocardial catheter and a left ventricular epicardial patch electrode. The first pulse was delivered between the right ventricular apical and the superior vena caval electrode on the right ventricular endocardial catheter. The second pulse was delivered between the right ventricular apical electrode and the left ventricular patch electrode 0.2 ms after termination of the first pulse. Single-pulse defibrillation was performed with a standard intracardiac defibrillation system in which a single truncated exponential pulse was delivered across 2 epicardial patch electrodes positioned over the anterolateral right ventricle and the posterolateral left ventricle. During defibrillation threshold determination, voltage and current waveforms were recorded and integrated to determine delivered energy. Average defibrillation threshold leading-edge voltage for the sequential pulse technique was 496 +/- 140 V, compared with 365 +/- 157 V for the single-pulse technique (p less than 0.005). Defibrillation threshold leading-edge current for the sequential-pulse technique was 6.0 +/- 2.3 A, compared with 10.6 +/- 5.1 A for the single-pulse method (p less than 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1987

Effects of pulsatile reperfusion on postischemic recovery of myocardial function after global hypothermic cardiac arrest.

It has been postulated that pulsatile blood flow helps to preserve the myocardium after ischemia. However, its effect on postischemic myocardium during cardiopulmonary bypass has not been clearly defined. To determine if pulsatile reperfusion improves postischemic recovery of cardiac metabolism and performance, we subjected 20 dogs to 60 minutes of aortic cross-clamping followed by 45 minutes of pulsatile (P group; 10 dogs) or nonpulsatile (NP group; 10 dogs) reperfusion. Left ventricular function was measured at a controlled preload in both groups before induction of global ischemia and after termination of bypass. Segmental length (assessed by sonomicrometry) was used to determine dimensional changes. Ventricular pressures were measured with solid-state micromanometers. Percent recovery of left ventricular peak systolic pressure, its first derivative, and stroke work were 66%, 59%, and 38%, respectively in the NP group and 82%, 76%, and 65% in the P group. The postarrest decrease in segmental shortening was minimized in the P group; left ventricular function curves and the slope of the end-systolic pressure-length relationship also indicated better performance after pulsatile reperfusion than after nonpulsatile reperfusion. Myocardial lactate extraction was transiently improved during the early pulsatile reperfusion period. We conclude that pulsatile reperfusion provides better myocardial preservation than nonpulsatile perfusion after 60 minutes of induced global ischemia.

Animals↗
PubMed1986

Effects of lobar pulmonary blood flow on the evolution of oleic acid lung injury in dogs.

We studied the effects of interruption of the pulmonary blood flow to the left diaphragmatic lung lobe on the evolution of canine oleic acid lung injury. We compared the morphology and edema of the left diaphragmatic lobe, whose pulmonary artery was ligated immediately after oleic acid injury, with the right diaphragmatic lobe, in which the blood supply was intact. The injury plus ligation resulted in hypoxemia and pulmonary hypertension with PaO2 falling from 98 +/- 4 to 72 +/- 21 torr (P less than 0.05) and pulmonary artery pressure increasing from 11 +/- 3 to 18 +/- 4 mm Hg (P less than 0.05). Animals were sacrificed 48 hr following the injury. Morphological examination of right and left lobes showed no consistent differences although wet/dry ratios indicated significantly greater edema (P less than 0.01) for the right diaphragmatic lobes (7.66 +/- 1.23) than the left (6.80 +/- 0.59). Both right and left lobes were substantially more edematous than our laboratory normal value of 4.74 +/- 0.54 (P less than 0.001 for both). We conclude that interruption of pulmonary arterial blood flow protects against edema formation in oleic acid injury but does not alter the morphologic evolution of the injury.

Animals↗
PubMed1986

Patch closure of aortic annulus mycotic aneurysms.

Twenty-three patients with bacterial endocarditis and mycotic aneurysms of the aortic annulus were treated between 1978 and 1985. There were 18 men and 5 women ranging from 24 to 72 years old. All patients had congestive heart failure and positive blood cultures as a complication of the endocarditis and were in New York Heart Association (NYHA) Functional Class III or IV. The aneurysm complicated late prosthetic valve endocarditis in 7 patients and native valve endocarditis in 16. The most common infecting organisms were streptococci (12 patients) and staphylococci (7 patients). The noncoronary sinus was the most frequent site for aneurysm formation. Following debridement of the abscess cavity, the orifice of the aneurysm was closed with a patch of Dacron in 20 patients and autologous pericardium in 3. A prosthetic valve (18 bioprosthetic and 5 mechanical) was secured to the noninfected portion of the native annulus and to the patch at the level of annulus. There were 3 deaths, 1 perioperative and 2 late, each without evidence of residual infection or aortic insufficiency. There are 20 late survivors (87%). After a mean follow-up of 1 year, all patients are in NYHA Functional Class I. Patch closure of mycotic aneurysms involving the aortic annulus permits aggressive debridement of the abscess cavity and affords closure of the orifice without tension. The prosthetic valve can be seated at the level of the native annulus, thus avoiding complicated reconstructive procedures of the aortic root and coronary arteries. This technique is an effective alternative in selected cases of mycotic aneurysms involving the aortic annulus.

Adult↗
PubMed1986

Simplified technique for pericardial patch of the right ventricular outflow tract.

Pericardial patching to enlarge the right ventricular outflow tract is often required in congenital cardiac surgery in lesions such as tetralogy of Fallot, pulmonary atresia, pulmonary stenosis, and pulmonary artery repair following removal of a palliative pulmonary artery band. A method of simplifying the attachment of the pericardial patch onto the right ventricular outflow tract is described.

Heart Defects, Congenital↗
PubMed1986

Combined carotid and coronary disease--a conservative strategy.

The optimal approach to patients undergoing coronary bypass surgery for coronary artery disease with coexisting carotid disease is controversial. To determine the best approach to these patients, we screened carotid arteries in patients undergoing coronary artery bypass preoperatively with noninvasive ultrasonic duplex scanning. No correlation was noted between stroke and asymptomatic carotid disease in patients undergoing coronary revascularization. Prospective application of this finding in 2251 patients has yielded a very low incidence of perioperative stroke. We concluded that asymptomatic carotid arterial disease is not a significant risk to patients undergoing cardiopulmonary bypass and should be managed conservatively.

Carotid Artery Diseases↗
PubMed1986

Catheter-mediated electrical ablation: the relation between current and pulse width on voltage breakdown and shock-wave generation.

Barotrauma from arc induced shock waves may result in dangerous sequelae during ablation of arrhythmogenic foci. In this report, maximum pulse amplitude and pulse width determinations were made to assess avoidance of shock-wave generation using rectangular constant current pulses. Energy delivery appears to be optimal between 80-100 microseconds. If higher energies are required, multiple pulses will be needed to avoid barotrauma.

Animals↗
PubMed1986

Some factors affecting bubble formation with catheter-mediated defibrillator pulses.

Factors affecting bubble formation during delivery of defibrillator pulses to arrhythmogenic cardiac tissue via a catheter are unknown. We investigated the role of energy, electrode surface area, interelectrode distance, and electrode polarity on bubble formation and on current and voltage waveforms during delivery of damped sinusoidal discharges from a standard defibrillator to anticoagulated bovine blood. Gas composition was studied with mass spectrometry. Defibrillator energy settings were varied between 5 and 360 J. The principal catheter used for study was a Medtronic 6992A lead. Additional electrodes tested included 2, 5, and 10 mm long No. 6F, 7F, and 8F copper electrodes. Interelectrode distances used to assess the effect of anode-cathode spacing were 1, 5, 10, and 20 cm. Bubble volume increased linearly from 0.043 to 0.134 ml per cathodal pulse and from 0.030 to 3.50 ml per anodal pulse as energy settings were increased from 5 to 360 J (r = .99). Typical smooth waveforms for both current and voltage were seen only in the absence of bubbles. The voltage waveform was distorted for each cathodal pulse of 100 J or more and for each anodal pulse of 10 J or more only if bubbles were present. The effect of electrode surface area on bubble formation was tested at a 200 J energy setting and at a 10 cm interelectrode distance with the use of cathodal pulses. Bubble formation varied inversely with electrode surface area (r = .876). Bubble formation, however, varied minimally as interelectrode spacing was changed from 1 to 20 cm. The effect of polarity on bubble formation when the Medtronic 6992A distal electrode and an 8.5 cm disk electrode separated by 10 cm were used was highly significant. For a 200 J pulse, bubble formation with the catheter as anode was 3.30 +/- 0.10 ml and with the catheter as cathode it was 0.070 +/- 0.002 ml (p less than .001). Mass spectrometry of both anodal and cathodal gas samples demonstrated the constituents of the gas bubble to include a variety of gases, which is inconsistent with simple electrolytic production of the bubbles observed. The predominance of nitrogen in either polarity sample suggested that the principal source of the bubble was dissolved air. In summary, bubble formation at an electrode receiving damped sinusoidal outputs from a standard defibrillator does not vary significantly with varying interelectrode distance. However, it is directly proportional to energy and inversely proportional to electrode surface area. Anodal catheter discharges produce considerably more bubbles than do cathodal discharges.(ABSTRACT TRUNCATED AT 400 WORDS)

Catheterization↗
PubMed1986

Effects of varying electrode configuration with catheter-mediated defibrillator pulses at the coronary sinus orifice in dogs.

We compared two methods of delivering single damped sine-wave defibrillator pulses to the coronary sinus orifice in 20 dogs. Ten dogs had "unipolar" (coronary sinus to precordial disc) and 10 had "bipolar" (coronary sinus proximal to coronary sinus distal electrode) discharges. Delivered voltage, current, and energy were recorded during each pulse. Electrophysiologic testing was done before and 4 weeks after the procedure. Histologic examination of the atrioventricular groove was done at 1 mm serial sections. For the unipolar configuration a 200 J defibrillator pulse resulted in a peak voltage of 3370 +/- 125 V, a peak current of 21 +/- 4 A, and a delivered energy of 253 +/- 29 J as compared with 3010 +/- 99 V, 70 +/- 4 A, and 144 +/- 18 J, respectively, for the bipolar configuration (p less than .001). Three dogs (two with bipolar, one with unipolar pulses) had gross coronary sinus rupture and died from acute pericardial tamponade. In addition, irrespective of electrode configuration, all dogs showed microscopic rupture of the coronary sinus internal elastic membrane. Transmural atrial scarring occurred in all 10 dogs that received a unipolar pulse but in only two dogs that received a bipolar pulse (p = .0004). Unlike the atrium, injury to the left ventricle was limited in both groups. Similarly, injury to the periannular myocardium was inconsistent and not transmural in either group. No significant electrophysiologic changes were observed. With the present technique, unipolar rather than bipolar catheter-mediated defibrillator pulses result in transmural atrial injury that might prevent accessory pathway conduction. Regardless of electrode configuration, high-energy defibrillator pulses consistently cause some degree of coronary sinus rupture, most likely related to a barotraumatic mechanism.

Animals↗