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Biomedical subjects

D K Murdock

Publications and source records attributed to D K Murdock.

49 records · Page 3Linked to original sources
PubMed1985

In vivo effects of acute changes in osmolality and sodium concentration on myocardial contractility.

Effects of acute changes in osmolality and sodium concentration (Na) on myocardial contractility (MC) were examined in anesthetized dogs. Using a carotid to left anterior descending bypass, 4 cc of NaCl and/or dextrose of varying osmolality as injected and the percentage of change in MC measured. At Na = O mEq/L, a positive inotropic response occurred, which varied inversely as osmolality increased from 300 (MC = 100 +/- 23%) to 700 mOsm/L (MC = 39 +/- 10%, p less than 0.01). Similar ranges of positive responses of lesser magnitude were noted at Na = 75 mEq/L. At Na = 150, 190, or 350 mEq/L, similar increments in osmolality caused an increasingly negative inotropic response. An inverse relationship between Na and MC was noted with osmolality held constant. Injections of the nonionic contrast agent, P297, in 5% dextrose or 0.9% NaCl, resulted in 28 +/- 3% or -17 +/- 4% (p less than 0.01) change in MC, respectively. Sodium concentration and osmolality have independent effects on MC. Hyperosmolality/hypernatremia causes a negative inotropic response while hyponatremia causes a positive one.

Animals↗
PubMed1985

The use of programmed electrical stimulation to assess the fibrillatory propensity of ionic and nonionic contrast media.

Coronary angiography occasionally results in ventricular fibrillation. To compare the fibrillatory propensity of conventional ionic and nonionic contrast media, we measured QT intervals and performed programmed electrical stimulation during intracoronary injection of Renografin 76 (R76), Hypaque 76 (H76), and iopamidol (IOP) in 16 open chest dogs. In ten dogs the incidence of ventricular fibrillation following induction of a single premature ventricular beat after every fourth atrial paced beat was 19/20 with R76, 8/20 with H76, and 0/20 with IOP (P less than .001). When two premature beats were induced, the incidence of ventricular fibrillation was 20/20 with R76, 19/20 with H76, and 1/20 with IOP (P less than .001). In six additional dogs, the mean prolongation of the QT interval was 170 +/- 20 msec with R76, 105 +/- 14 msec with H76, and 63 +/- 9 msec with IOP (P less than .001). Thus, programmed electrical stimulation readily induces ventricular fibrillation during intracoronary injection of conventional ionic contrast media. The incidence of ventricular fibrillation parallels the amount of QT interval prolongation produced. H76, which lacks EDTA and sodium citrate, is less fibrillatory than R76. However, the nonionic medium IOP appears far less fibrillatory than either R76 or H76.

Angiography↗
PubMed1985

Pacemaker malfunction simulated by amplifier saturation.

In this case report, pacemaker malfunction is simulated by prolonged pauses after each pacemaker discharge. The pauses were due to saturation of the input of the telemetry monitor amplifier by the discharge voltage of the pacemaker. It is important to recognize amplifier saturation as a form of artifact that can mimic pacemaker malfunction.

Aged↗
PubMed1984

Ventricular fibrillation during coronary angiography in dogs: the role of calcium-binding additives.

Coronary angiography with Renografin 76 (RG76) occasionally results in ventricular fibrillation (VF). Angiovist 370 (AV370) is a contrast medium similar to RG76 except the calcium-sequestering agents, sodium citrate and EDTA in RG76 have been replaced by calcium EDTA. To determine whether these sequestering agents contribute to contrast medium-induced VF, a comparison was made of the effects of intracoronary injections of RG76, AV370, and saline solutions containing sodium citrate and EDTA (CIT/EDTA) and calcium EDTA (CA EDTA) on myocardial conduction, local QT intervals, and incidence of spontaneous and induced VF in 32 dogs. Four milliliters of RG76 produced a 111 +/- 12-ms increase in local QT intervals, compared with a 73 +/- 8-ms increase with AV370 (p less than 0.001). Spontaneous VF occurred in 12 of 16 six-milliliter injections of RG76, compared with 4 of 16 injections of AV370 (p less than 0.02) An early-cycle premature impulse applied after every fourth beat induced VF in 15 of 16 four-milliliter injections of RG76 compared with 5 of 16 injections of AV370 (p less than 0.01). As the premature beat conducted through the left anterior descending region, conduction slowing and fractionation occurred, which was less with AV370 than with RG76. The CIT/EDTA solution produced a greater increase in QT intervals (77 +/- 5 ms) than the CA EDTA solution (29 +/- 3 ms) or 0.9% saline solution alone (28 +/- 2 ms) (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Inotropic effects of ionic contrast media: the role of calcium binding additives.

Renografin-76 (RG76) regularly depresses myocardial contractility during coronary angiography. Angiovist-370 (AV370) is a contrast medium similar to RG76 except the calcium sequestering agents sodium citrate and EDTA in RG76 have been replaced by calcium EDTA (an additive that does not bind additional calcium). To determine if the calcium sequestering agents contribute to the mechanical depression produced by ionic contrast media, this study compared the inotropic response of RG76 to that of AV370. Additionally, saline solutions containing sodium citrate + EDTA and calcium EDTA at concentrations found in the respective contrast media were also compared. In 10 open chest dogs the percent change and duration of the inotropic response following intracoronary injections of RG76 and AV370, as well as solutions of sodium citrate + EDTA and calcium EDTA were compared using Walton-Brodie strain gauges. Injections, 2 cc, of RG76 and AV370 produced a biphasic response characterized by an initial negative inotropic response followed by a more prolonged positive inotropic response. The magnitude (67 +/- 3% vs 59 +/- 2%; p less than 0.001) and duration (34 +/- 3 vs 24 +/- 2 sec; p less than 0.001) of the initial negative inotropic response was greater with RG76 than with AV370. The magnitude of the secondary positive inotropic response with RG76 was not different from that obtained with AV370 (31 +/- 12% vs 28 +/- 10%; p greater than 0.3). This positive response was not affected by beta-adrenergic blockage with 0.2 mg/kg of timolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1979

Supraventricular pacemaker underdrive in the absence of sinus nodal influences in the conscious dog.

The ability to reduce and maintain heart rate by electrical stimulation (underdrive) was tested in three groups of chronically instrumented dogs: sinoatrial node intact, ectopic atrial pacemaker produced by injection of rapidly hardening latex into the sinoatrial nodal artery, and idioventricular pacemaker produced by injection of formalin into the atrioventricular node. In the conscious unsedated state, underdrive of sinoatrial or idioventricular pacemakers resulted in competition between driven and intrinsic foci. However, the cycle length of ectopic atrial pacemakers could be increased by 148.4 +/- 30.7 msec (P less than 0.001) and maintained at that value. Cessation of underdrive resulted in a period of pacemaker suppression similar to that produced following overdrive. Single premature stimuli produced marked cycle length prolongations in dogs with ectopic atrial foci. Total autonomic blockade had no significant effect on the production of underdrive. Thus, the results of the present experiments provide evidence for maintained capture of cardiac pacemakers at rates significantly below intrinsic control and indicate that underdrive varies as a function of pacemaker site. Underdrive may explain the failure of junctional escape in the presence of slower atrial rhythms.

Animals↗
PubMedDate not supplied

Medicare's Cooperative Cardiovascular Project: can we trust our MetaStar report cards? Cardiovascular Care Committee of Wausau Hospital.

The purpose of Medicare's Cooperative Cardiovascular Project (CCP) is to improve the care of Medicare patients presenting with acute myocardial infarction (AMI). MetaStar is Wisconsin's Medicare peer review organization that administers Phase II of the CCP. A major Phase II objective is to increase the use of reperfusion strategies (thrombolysis and angioplasty) and angiotensin converting enzyme (ACE) inhibitors (when the ejection fractions is < 40%) in patients presenting with AMI. After MetaStar presented Wausau Hospital's baseline Phase II data to us, we were asked to define a plan to improve the use of reperfusion therapy and ACE inhibitors. To verify the accuracy of the data presented to us, we reviewed the patient records used by MetaStar to calculate our baseline data for these 2 quality-of-care indicators. Our MetaStar reported reperfusion rate (48.4%) and ACE inhibitor rate (20.9%) were significantly different from that which we calculated (100% and 97%). Causes for the discrepancy included MetaStar abstractor's failure to exclude two patients who did not have an AMI, failure to correctly count patients who received the targeted treatment, and an inability of the abstractors to identify important CCP exclusion criteria. Thus, numerous patients who should have been excluded were inappropriately classified as "ideal" candidates for the targeted therapy. WE CONCLUDE: There are major flaws in the data collection techniques used by MetaStar in Phase II of the CCP. These flaws produced erroneous conclusions concerning our use of reperfusion strategies and ACE inhibitors. Since these quality-of-care indicators are major targeted goals of Phase II, the errors are of special concern. We believe better-designed abstract forms, due diligence, and more thorough training could have prevented the errors. In presenting our concerns, we hope to foster a response by MetaStar to improve the quality of the peer review process.

Angiotensin-Converting Enzyme Inhibitors↗
PubMedDate not supplied

Use of power spectral analysis of respiratory sinus arrhythmia to detect graft rejection.

Some evidence has suggested that graft rejection in heart transplant recipients is accompanied by sinus node dysfunction. To test this hypothesis the electrocardiograms of 21 orthotopic heart transplant recipients receiving cyclosporine were recorded at regularly scheduled biopsies. This resulted in 105 good quality recordings of at least 10 minutes each. All exhibited normal sinus rhythm. These recordings were then processed through patented digital routines that calculated the power spectrum of the RR intervals. All recordings exhibited Mayer wave and respiratory sinus arrhythmia (RSA) periodicities. Peak spectral power of RSA (PSP-RSA) demonstrated good repeatability at 2 weeks (r = 0.81). A paired t test comparing the baseline PSP-RSA in eight subjects who experienced rejection episodes with their individual average PSP-RSA during periods of rejection revealed a significant decrease (p = 0.039). As a global measure, PSP-RSA greater than 1 (natural logarithmic scales) demonstrated a sensitivity of 1.0, specificity of 0.42, positive predictive value of 0.22, and negative predictive value of 1.0. These tentative results demonstrate that PSP-RSA may be a sensitive, noninvasive marker for graft rejection of heart transplant patients receiving cyclosporine for immunosuppression. A larger, more extensive study needs to be conducted to confirm these results.

Adult↗
PubMedDate not supplied

The effect of heart transplantation on Cheyne-Stokes respiration associated with congestive heart failure.

Cheyne-Stokes respiration occasionally accompanies the terminal stages of congestive heart failure. We describe this association in a patient requiring heart transplantation. The gradual abatement of Cheyne-Stokes respiration after transplantation supports the delayed circulatory time theory as the mechanism for Cheyne-Stokes respiration in these patients.

Cheyne-Stokes Respiration↗