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Biomedical subjects

S T Higano

Publications and source records attributed to S T Higano.

14 recordsLinked to original sources
PubMed1995

Intravascular ultrasound to assess anastomotic patency after lung transplantation.

Pulmonary arterial anastomotic stenosis is an unusual complication after single-lung transplantation. Intravascular ultrasound, performed at the bedside with an introducer sheath and guidewire, is a new technique that provides high-resolution tomographic images of the anastomotic site. This modality was used early in the postoperative course of a 58-year-old man to exclude significant pulmonary arterial anastomotic narrowing after right single-lung transplantation for primary pulmonary hypertension.

Constriction, Pathologic↗
PubMed1995

Epicardial vasomotor responses to acetylcholine are not predicted by coronary atherosclerosis as assessed by intracoronary ultrasound.

OBJECTIVES: The purpose of this study was to use intravascular ultrasound to determine the morphologic appearance of the coronary arteries, relating the absence, presence and extent of atherosclerosis to the response of the coronary arteries to acetylcholine infusion. BACKGROUND: Endothelial function plays a major role in the pathophysiology of myocardial ischemia and angina pectoris. The response of the coronary arteries to selective infusion of acetylcholine has been used to examine endothelial function, with vasoconstriction occurring in the absence of intact endothelial function. Vasoconstriction to acetylcholine infusion in humans without overt coronary artery disease has been attributed to early atherosclerosis not detected by coronary angiography. METHODS: Twenty-nine patients without overt coronary artery disease underwent selective coronary angiography and selective intracoronary infusion of increasing concentrations of acetylcholine (10(-6), 10(-5) and 10(-4) mol/liter), followed by intravascular ultrasound imaging. RESULTS: The response of the coronary arteries to acetylcholine infusion was not dependent on the absence or presence of atherosclerotic plaque, as detected by intravascular ultrasound. The percent change in epicardial coronary artery diameter during acetylcholine infusion versus baseline was -14 +/- 28% (mean +/- SD) in the seven patients with no visible atherosclerosis on intravascular ultrasound versus -9 +/- 20% in the 22 patients with visible atherosclerosis on intravascular ultrasound (p = NS, confidence interval -14% to 25%). There was a greater vasoconstrictive response to acetylcholine infusion in patients with risk factors for coronary artery disease than in those without risk factors (p = 0.003). CONCLUSIONS: The vasoreactive response to acetylcholine is not necessarily dependent on ultrasound detection of the presence or absence of atherosclerosis.

Acetylcholine↗
PubMed1991

Standardized informal exercise testing for programming rate adaptive pacemakers.

It is essential that patients with pacemakers capable of rate modulation undergo some form of exercise testing to assure appropriate rate modulation. Informal exercise testing is a reasonable and less expensive alternative to formal treadmill testing. Empiric adjustment of the rate response parameters by assessing the patient's rate response while walking at a self-determined casual and brisk pace has been used. However, no normals exist to determine the appropriate rate response for a "casual" and "brisk" walk. Volunteers were tested with metronome-guided casual and brisk walks in an effort to standardize the informal exercise and determine expected heart rate response for these levels of activity. Results of the metronome-guided rate response in normal volunteers may be useful in determining the appropriate rate response for pacemaker patients when tested in such an informal manner.

Adult↗
PubMed1990

The mechanism of blood flow during closed chest cardiac massage in humans: transesophageal echocardiographic observations.

Despite years of research, the mechanism of forward blood flow during closed chest cardiac massage remains controversial. Two theories have been suggested: the cardiac pump theory and the thoracic pump theory. Transesophageal echocardiography offers a new approach for study of the flows and cardiac morphologic features during chest compressions in humans. Case reports are presented to illustrate the use of transesophageal echocardiography during cardiopulmonary resuscitation. The findings included right and left ventricular compression, closure of the mitral valve during compression, opening of the mitral valve during the release phase, and atrioventricular valvular regurgitation during compression, indicating a positive ventricular-to-atrial pressure gradient. These findings suggest that direct cardiac compression was the predominant mechanism of forward blood flow during cardiopulmonary resuscitation in these patients. An understanding of the actual mechanisms involved is necessary if improved cardiopulmonary resuscitative techniques or adjuncts are to be rationally developed for enhancing the outcome of resuscitation.

Aged↗
PubMed1990

Venous obstruction due to permanent transvenous pacemaker electrodes: treatment with percutaneous transluminal balloon venoplasty.

Transvenous placement of permanent pacemaker leads is currently the most common method for permanent cardiac pacing. Venous abnormalities, in particular venous stenosis or thrombosis (or both) frequently have been described, although most patients remain asymptomatic because of the development of an adequate venous collateral circulation. Venous obstruction often first becomes apparent during pacemaker lead revision, when difficulty passing the new pacing lead is encountered. In this report, we present two cases of venous stenosis and thrombosis due to permanent transvenous pacemaker electrodes and the use of percutaneous transluminal balloon venoplasty to relieve the venous obstruction.

Aged↗
PubMed1990

Facilitation of the subclavian-introducer technique with contrast venography.

The subclavian-introducer technique is a rapid and easily performed method of obtaining venous access for implanting permanent pacemaker electrodes. Although this technique has facilitated the participation of nonsurgeons in pacemaker implantation, the potential for complications is increased over the venous cutdown approach. This is particularly true in difficult cases, such as those with prior lead implants, venous thrombosis, or anomalous venous return. This article describes the use of contrast venography for facilitating an otherwise "blind" subclavian venipuncture. This method should make use of the subclavian-introducer technique safer.

Catheterization, Peripheral↗
PubMed1990

Quantitative analysis of Wenckebach behavior in DDD pacemakers.

Wenckebach-type behavior in P-synchronous pacing modes allows a gradual transition into 2:1 block. As this behavior is dependent on precise timing intervals, it can be quantitated with mathematical equations. In this report, equations for quantitating the Wenckebach escape rate and the (N + 1)/N block points have been derived. These equations were then used to produce plots of Wenckebach escape rates for given AV intervals, atrial refractory periods, and atrial rates. These equations were validated utilizing a DDD pulse generator interfaced with a patient simulation device. The predicted values for the Wenckebach escape rate and ratio (n = 33) correlated highly with the observed values (r = 0.99, P less than 0.0001, and r = 0.97, P less than 0.0001, respectively) thereby validating the derived equations. This quantitative analysis has allowed a close look at the pacing behavior between the maximum tracking rate and the 2:1 block point. These equations may be clinically useful for assessing whether a nontriggering P wave resulted from Wenckebach type block or atrial undersensing and for the more complicated interval analysis in DDDR pacing with rate responsive AV delays and postventricular atrial refractory periods.

Computer Simulation↗
PubMed1989

Advantage of discrepant upper rate limits in a DDDR pacemaker.

The latest cardiac pacing mode to become available is the dual-chamber, rate-modulated mode (referred to as DDDR), which restores both rate responsiveness and atrioventricular synchrony in patients with sinus node dysfunction and atrioventricular block. This pacing mode combines dual-chamber and single-chamber rate-modulated technologies. Thus, it is necessary to program both a maximum tracking rate and a maximum sensor rate, as in dual-chamber and single-chamber rate-modulated devices, respectively. These two upper rate limits are usually programmed to equivalent values. The case described herein illustrates one advantage of programming discrepant upper rate limits. The rapid tracking of supraventricular tachycardias was prevented by lowering the maximum tracking rate to 100 ppm. A maximum sensor rate of 140 ppm still allowed an adequate rate response during activity.

Aged↗
PubMed1989

Utility of rate histograms in programming and follow-up of a DDDR pacemaker.

Dual-chamber, rate-modulated pacing (DDDR) is the newest available pacing mode. To optimize programming of the rate response options for such a pacemaker, the physician must adopt an organized follow-up method, including use of some type of exercise testing to assess the programmed options of the pacemaker. Because the patient may achieve a substantial "training effect" after a rate-modulated pacing device has been implanted, the device probably should be reprogrammed at 1 month or after implantation. Programming and follow-up can be considerably facilitated by the use of pacemaker-generated "rate histograms," which conveniently display the distribution of rate responses to various levels of activity.

Adult↗
PubMed1989

P wave tracking above the maximum tracking rate in a DDDR pacemaker.

Dual-chamber, rate-modulated pacemakers have recently become available. These devices, whose rate response is determined by the combined input from the intrinsic atrial rate and the sensor-driven rate, have led to some unexpected upper rate behaviors. In the case presented, with the maximum sensor pacing rate at 150 ppm, multiple episodes of apparent P wave tracking occurred above the maximum P wave tracking rate of 100 ppm. This behavior is explained by P waves that inhibit sensor-driven atrial output; inhibition may result in variable maximum tracking rates that are equal to the current sensor-driven rate. This effect appears to have minimal physiological consequence. Its importance lies in its recognition as normal DDDR function so that searches for pacemaker malfunction will not be made.

Adult↗
PubMed1989

Electrocardiographic manifestations of a dual-chamber, rate-modulated (DDDR) pacemaker.

Dual-chamber, rate-modulated pacing (DDDR) has only recently been made available. During exercise, the pacemaker is capable of tracking not only the patient's intrinsic P wave but also the AV sequential sensor-indicated rate response, which depends on the programmed variables of the specific sensor in the DDDR pulse generator. Programmed options that affect the operation of a rate-modulated DDDR device are slope, threshold, reaction time, and recovery time. In addition, one is required to program a base or minimum pacing rate and a maximum tracking rate, as in any DDD device, as well as a maximum sensor rate. It is essential to know and understand all these programmed options if one is to correctly interpret electrocardiograms from a DDDR pacemaker. Interpreting the electrocardiograms also requires an understanding of the sensor-indicated rate of the pacemaker at any given level of exercise, which is determined by the options previously listed and the interaction between the sensor-indicated rate and the patient's intrinsic atrial and ventricular activity. This paper presents electrocardiograms typical of a new DDDR pacemaker undergoing clinical investigation.

Cardiac Pacing, Artificial↗
PubMed1989

Sensor-driven rate smoothing in a DDDR pacemaker.

DDD pacemakers may have large cycle-to-cycle variations in rate at the upper rate limit because of 2:1 block or Wenckebach-type block. Rate smoothing was introduced as an option to eliminate these large variations. Now, DDDR pacemakers can produce similar electrocardiographic displays through a different mechanism that uses an activity sensor. This is termed "sensor-driven rate smoothing" because it occurs only when the activity sensor is driving the pacemaker. In the case described, as the atrial rate exceeded the maximum tracking rate and reverted to Wenckebach-type block, the RR interval varied only from 600 msec to 680 msec (13.3% rate-smoothing value) because of sensor-driven pacing. Maximal sensor-driven rate smoothing requires optimal programming of the rate response indicators. This sensor-driven rate-smoothing effect is an electrocardiographic manifestation that will undoubtedly be seen more frequently as DDDR devices come into widespread clinical use.

Adult↗
PubMedDate not supplied

Methylergonovine-induced diffuse coronary spasm in a patient with exercise-induced coronary spasm after heart transplantation.

Coronary artery spasm is a rarely reported condition after heart transplantation. We report a case of exercise-induced coronary artery spasm in a patient 1-year after orthotopic heart transplantation. Serial quantitative coronary angiography showed significant diffuse loss of luminal diameter. Provocative testing with intracoronary acetylcholine and intravenous methylergonovine maleate was performed in an effort to document efficacy of the antispasm regimen. Infusion of acetylcholine into the left anterior descending coronary artery resulted in transient closure of the vessel. Diffuse spasm resulting in hypotension and ventricular fibrillation occurred with intravenous methylergonovine maleate administration. Because of the risk of provoking diffuse spasm, intravenous administration of methylergonovine maleate should be avoided in the posttransplantation setting. Review of the literature suggests that coronary artery spasm after transplantation is often associated with severe transplant coronary artery disease and may be associated with a poor prognosis. Coronary artery spasm may be a more common cause of syncope and death after transplantation than it is currently thought to be.

Acetylcholine↗