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Biomedical subjects

C C Gornick

Publications and source records attributed to C C Gornick.

At least 19 recordsLinked to original sources
PubMed2001

The utility of ultrasound to determine ventricular capture in external cardiac pacing.

Determining electrical capture when using an external cardiac pacemaker is often difficult and confusing, especially when the resulting clinical signs of an effective blood pressure and pulse are inadequate or nondetectable. The objective of this study was to determine the efficacy of using 2-dimensional ultrasound (US) in determining the presence of ventricular capture of an external cardiac pacemaker in a swine model. Five anesthetized swine underwent external cardiac pacing (ECP) at variable levels of energy output while concurrent US images and electrocardiograph monitoring were recorded on videotape. Determinations of capture/no capture were made in the laboratory. Segments of videotape were selected to be reviewed by 2 physicians blinded to these laboratory determinations of capture and to each other. Kappa levels of agreement were determined among the 3 pairs of comparisons. Seventeen segments were reviewed. Kappa levels of agreement were 0.76 for Reviewer A versus Laboratory determination, 0.88 for Reviewer B versus Laboratory determination, and 0.88 for Reviewer A versus Reviewer B. All P values were <.001. These excellent levels of agreement show that 2D US in this animal model is highly effective in determining the presence of ventricular capture in ECP.

Animals↗
PubMed2000

Heart rate recovery post-exercise as an index of parasympathetic activity.

The time constant (T) obtained by fitting post-exercise heart rate (HR) recovery to a first order exponential decay curve has been promoted as an index of parasympathetic activity. However, acceptance has been limited because reported data are inadequate to assess goodness of fit for the model, determine the best exercise protocol, or optimize the duration of post exercise monitoring. Consequently, we evaluated T for nine healthy volunteers (age 24-46) following treadmill exercise at maximal (max) and two stages sub-max exercise (Bruce protocol). T stabilized only after 3 min of post-exercise monitoring. With max exercise, T varied unacceptably with small changes in onset of monitoring, e.g. -16.7+/-16.6 (-13.2%) in the first 5 s, and residuals of the fitted curve were non-random. In contrast, sub-max exercise produced consistent T values, e.g. -1.9+/-3.2 (-4.2%) in the first 5 s, and residuals were more nearly random. In conclusion, first order decay is an inadequate model for HR recovery following max exercise, but may be reasonable for sub-max levels.

Adult↗
PubMed2000

Endocardial activation during ventricular fibrillation in normal and failing canine hearts.

Because congestive heart failure (CHF) promotes ventricular fibrillation (VF), we compared VF in seven dogs with CHF induced by combined myocardial infarction and rapid ventricular pacing to VF in six normal dogs. A noncontact, multielectrode array balloon catheter provided full-surface real-time left ventricular (LV) endocardial electrograms and a dynamic color-coded display of endocardial activation projected onto a three-dimensional model of the LV. Fast Fourier transform (FFT) analysis of virtual electrograms showed no difference in peak or centroid frequency in CHF dogs compared with normals. The average number of simultaneous noncontiguous wavefronts present during VF was higher in normals (2.4 +/- 1.0 at 10 s of VF) than in CHF dogs (1.3 +/- 1.0, P < 0.005) and decreased in both over time. The wavefront "turnover" rate, estimated using FFT of the noncontiguous wavefront data, did not differ between normals and CHF and did not change over 5 min of VF. Thus the fundamental frequency characteristics of VF are unaltered by CHF, but dilated abnormal ventricles sustain fewer active wavefronts than do normal ventricles.

Animals↗
PubMed2000

Anticoagulant use in nonvalvular atrial fibrillation. Determining risk and choosing the safest course.

Previous TIA or stroke, diabetes, advanced age, impaired left ventricular function, and a history of hypertension are strong risk factors in patients with nonvalvular AF. When none of these factors is present, aspirin in a dose of 325 mg offers effective protection against future stroke. When any of these factors are present, warfarin adjusted to an INR of 2.0 to 3.0 offers greater protection against future stroke than aspirin alone or aspirin and fixed-dose warfarin (INR 1.2-1.5). More data are needed before newer anticoagulants can be recommended for treatment.

Anticoagulants↗
PubMed1999

Validation of a new noncontact catheter system for electroanatomic mapping of left ventricular endocardium.

BACKGROUND: Improvements in cardiac mapping are required to advance our understanding and treatment of arrhythmias. This study validated a new noncontact multielectrode array catheter and accompanying analysis system to provide electroanatomic mapping of the entire left ventricular (LV) endocardium during a single beat. METHODS AND RESULTS: A 9F 64-electrode balloon array catheter with an inflated size of 1.8x4.6 cm was used to simultaneously record electrical potentials generated by the heart and locate a standard electrophysiology (EP) catheter within the same chamber. By use of the recorded location of the EP-catheter tip, LV geometry was determined. Array potentials served as inputs to a high-order boundary-element method to produce 3360 potential points on the endocardial surface translatable into electrograms or color-coded activation maps. Three methods of validation were used: (1) driven electrodes in an in vitro tank were located; (2) waveforms generated from the array catheter were compared with catheter contact waveforms in canine LV; and (3) sites of local LV endocardial activation were located and marked with radiofrequency lesions. Tank testing located a driven electrode to within 2.33+/-0.44 mm. Correlation of timing and morphology of computed versus contact electrograms was 0.966. Radiofrequency lesions marked 17 endocardial pacing sites to within 4.0+/-3.2 mm. CONCLUSIONS: This new system provides anatomically accurate endocardial isopotential mapping during a single cardiac cycle. The locator component enabled placement of a separate EP catheter to any site within the mapped chamber.

Animals↗
PubMed1997

Electrophysiologic characteristics of a pulsed iontophoretic drug-delivery system in coronary arteries.

This study evaluated the electrophysiologic effects of a pulsed iontophoretic drug-delivery system when used in the coronary arteries. Prevention of acute thrombosis and restenosis after intravascular procedures may be enhanced by high concentrations of therapeutic agents within the vessel wall. A new intravascular drug-delivery system uses iontophoresis to maximize local tissue concentrations of drug. However, the electrophysiologic effects of such a system in coronary arteries are unknown. An iontophoretic membrane balloon-tipped catheter was placed fluoroscopically in the mid left anterior descending coronary artery of 10 anesthetized dogs. Strength-duration curves and effective refractory period (ERP) were initially determined. Threshold for capture was assessed at pulse widths of 0.5, 1.0, 2.0, 4.0, and 8.0 ms. Capture occurred at 4.9 +/- 0.9, 3.4 +/- 0.5, 2.6 +/- 0.5, 1.6 +/- 0.2, and 1.2 +/- 0.2 mA, respectively. The ERP was 169 +/- 6 ms (4.0-ms pulses at twice threshold). Then square-wave pulses for iontophoresis were R-wave synchronized and delivered at 50 and 75% of the ERP with the balloon inflated to 1 atm. Output was increased until significant arrhythmias occurred [premature beats > 10/min, supraventricular tachycardia (SVT), ventricular tachycardia (VT), ventricular fibrillation (VF)], by using sequential steps of 1, 5, 10, 15, and 20 mA. Highest average outputs achieved without an arrhythmia were 14.1 +/- 2.5 and 4.9 +/- 2.0 mA at 50 and 75% of ERP, respectively (p < 0.05). High-grade arrhythmias (pulseless VT or VF) occurred in three of four animals studied before use of a frequency limiter, which allowed current delivery only at intervals > 400 ms (thus inhibiting current activation during premature beats). No further VT or VF occurred in the remaining six animals, except for one episode of nonsustained VT (11 beats). An R-wave synchronized iontophoretic field with a response-frequency limiter can be safely used within the canine coronary arterial system at 50% of ERP with moderate outputs (5-10 mA). Increasing the stimulus duration to 75% of ERP increases arrhythmogenesis but is tolerated at lower output levels (< 5 mA).

Animals↗
PubMed1996

Cardiopulmonary support mitigates the effects of experimental myocardial ischemia.

The effectiveness of cardiopulmonary support (CPS) as a rescue method following failed angioplasty is unknown. The proximal left anterior descending (LAD) was occluded for 20 min in 21 dogs. Group 1 animals (n=15) were given CPS and group 2 animals (n=6) served as controls. During coronary occlusion, animals receiving CPS had increased mean arterial pressure (71+/- 12 vs 58+/-7 mm Hg), decreased left atrial pressure (3+/-3 vs 12+/-3 mm Hg), increased ischemic area blood flow (0.20+/-0.16 vs 0.02+/-0.04 mL/min/g) and myocardial oxygen consumption (0.014+/- 0.008 vs 0.003+/-0.006 mL O2/min/g), decreased remote area myocardial oxygen consumption (0.026+/-0.010 vs 0.091+/-0.047 mL O2/min/g), and an improved myocardial oxygen consumption index (0.60+/-0.33 vs 0.02+/-0.03) when compared with controls (p<0.05). During reperfusion (no CPS), group 1 animals had increased cardiac index (210+/-95 vs 117+/-46 mL/min/kg), renal blood flow (110+/-38% vs 53+/-45%), ischemic area blood flow (1.13+/-0.40 vs 0.58+/-0.27), and myocardial oxygen consumption (0.066+/-0.015 vs 0.032+/-0.018) when compared with controls (p<0.05). CPS improves oxidative metabolism in selective myocardial segments during coronary occlusion, promotes recovery of the postischemic myocardium, and results in improved peripheral circulation.

Angioplasty, Balloon, Coronary↗
PubMed1995

Role of transesophageal echocardiography in the detection of left atrial thrombus in patients with chronic nonrheumatic atrial fibrillation.

Transesophageal echocardiography was used to assess cardiac abnormalities associated with embolization in patients who had completed the Department of Veterans Affairs Cooperative Study of Stroke Prevention in Nonrheumatic Atrial Fibrillation at the Minneapolis and West Haven Department of Veterans Affairs Medical Centers without an embolic event. Patients were men, 71 +/- 7 years old, with atrial fibrillation of 6.2 +/- 4.3 years' duration who had received warfarin (n = 32) or placebo (n = 23) for 2 years. Thrombi were found in 5 of 55 patients (warfarin 4 and placebo 1; p = 0.39); spontaneous echo contrast was seen in 4 of 5 patients. Other abnormalities identified included spontaneous echo contrast (47%), patent foramen ovale (54%), atrial septal aneurysm (7.3%), and left ventricular thrombus (3.6%). During 34 months of posttreatment follow-up, 5 patients had a stroke (1 fatal), and 10 died. Potential sources of emboli did not predict subsequent outcome. Thus warfarin therapy did not preclude the presence of thrombi. Stroke reduction likely involves the prevention of emboli from sources in addition to the atrial appendage.

Aged↗
PubMed1994

Mildly symptomatic pulmonary emboli associated with electrophysiologic procedures. Indications for anticoagulant use.

Symptomatic pulmonary emboli complicating electrophysiologic procedures are uncommon. Asymptomatic or mildly symptomatic embolic are likely much more common. This case report highlights the problem of extensive, but mildly symptomatic, pulmonary emboli occurring as a complication of electrophysiologic procedures, including catheter ablation. The role of anticoagulation during and following electrophysiologic procedures in preventing pulmonary emboli (which can have long-term sequelae) is unknown. Currently, there appears to be no consensus regarding the use of anticoagulants either during or following electrophysiologic procedures, including those involving catheter ablation. Based on the presumed frequency and potential long-term complications of pulmonary emboli, anticoagulation during electrophysiologic procedures should be recommended.

Aged↗
PubMed1992

Warfarin in the prevention of stroke associated with nonrheumatic atrial fibrillation. Veterans Affairs Stroke Prevention in Nonrheumatic Atrial Fibrillation Investigators.

BACKGROUND: Nonrheumatic atrial fibrillation is common among the elderly and is associated with an increased risk of stroke. We investigated whether anticoagulation with warfarin would reduce this risk. METHODS: We conducted a randomized, double-blind, placebo-controlled study to evaluate low-intensity anticoagulation with warfarin (prothrombin-time ratio, 1.2 to 1.5) in 571 men with chronic nonrheumatic atrial fibrillation; 525 patients had not previously had a cerebral infarction, whereas 46 patients had previously had such an event. The primary end point was cerebral infarction; secondary end points were cerebral hemorrhage and death. RESULTS: Among the patients with no history of stroke, cerebral infarction occurred in 19 of the 265 patients in the placebo group during an average follow-up of 1.7 years (4.3 percent per year) and in 4 of the 260 patients in the warfarin group during an average follow-up of 1.8 years (0.9 percent per year). The reduction in risk with warfarin therapy was 0.79 (95 percent confidence interval, 0.52 to 0.90; P = 0.001). The annual event rate among the 228 patients over 70 years of age was 4.8 percent in the placebo group and 0.9 percent in the warfarin group (risk reduction, 0.79; P = 0.02). The only cerebral hemorrhage occurred in a 73-year-old patient in the warfarin group. Other major hemorrhages, all gastrointestinal, occurred in 10 patients: 4 in the placebo group, for a rate of 0.9 percent per year, and 6 in the warfarin group, for a rate of 1.3 percent per year. There were 37 deaths that were not preceded by a cerebral end point--22 in the placebo group and 15 in the warfarin group (risk reduction, 0.31; P = 0.19). Cerebral infarction was more common among patients with a history of cerebral infarction (9.3 percent per year in the placebo group and 6.1 percent per year in the warfarin group) than among those without such a history. CONCLUSIONS: Low-intensity anticoagulation with warfarin prevented cerebral infarction in patients with nonrheumatic atrial fibrillation without producing an excess risk of major hemorrhage. This benefit extended to patients over 70 years of age.

Aged↗
PubMed1990

Timing and magnitude of serum creatine kinase-MB after transcatheter cardiac tissue fulguration in man.

This study examined the impact of transcatheter fulguration on creatine kinase-MB release in 21 patients (age range 17-71 years). Arrhythmia diagnoses were ventricular tachycardia 9, atrial fibrillation with a rapid ventricular response 7, atrioventricular nodal reentry 2, and reciprocating tachycardia utilizing a posteroseptal accessory pathway 3. Seven patients had apparently normal hearts while 8 had ischemic heart disease and 6 cardiomyopathy. Timing of initial elevated creatine kinase-MB activity (mean 1.34 +/- 0.69 SD hours) and peak creatine kinase-MB activity (mean 3.73 +/- 0.89 SD hours) was relatively uniform in all patients. Time to peak creatine kinase-MB activity was unrelated to either underlying cardiac disease (normal: 3.9 +/- 1.0 hours; ischemic heart disease: 3.5 +/- 0.9 hours; cardiomyopathy: 3.8 +/- 0.9 hours), or fulguration site (His bundle (n = 9): 4.2 +/- 0.9 hours, proximal coronary sinus (n = 3): 3.3 +/- 0.3 hours, ventricle (n = 9): 3.4 +/- 0.8 hours). The magnitude of peak serum creatine kinase-MB activity was independent of myocardial diagnosis or fulguration site, but was linearly related to total energy delivered (r = 0.5, P less than 0.022). The latter correlation was particularly strong within cardiac diagnosis subgroups (normal: r = 0.92, P less than 0.002; ischemic heart disease: 0.73, P less than 0.04; non-ischemic cardiomyopathy: r = 0.57, P = NS). Thus, serum creatine kinase-MB activity following transcatheter fulguration is linearly related to the magnitude of delivered energy, and is similar to that observed after transient coronary artery occlusion and reperfusion.

Adolescent↗
PubMed1989

Provocation of bradycardia and hypotension by isoproterenol and upright posture in patients with unexplained syncope.

Neurally mediated hypotension and bradycardia are believed to be common causes of syncope. We used the "upright-tilt test" (duration, less than or equal to 10 minutes) with or without an infusion of exogenous catecholamine (isoproterenol [1 to 5 micrograms per minute], given intravenously) to elicit bradycardia, hypotension, or both in 24 patients with recurrent syncope and in 18 control subjects. A conventional electrophysiologic test performed before the tilt test was positive in 9 of the 24 patients, revealing arrhythmias that may have caused recurrent syncope, but was negative and thus nondiagnostic in 15 patients. The tilt test alone (i.e., without isoproterenol) induced symptomatic bradycardia or hypotension in 1 of the 9 patients with positive electrophysiologic tests (11 percent), 4 of the 15 patients with negative electrophysiologic tests (27 percent), and none of the controls. When the isoproterenol infusion was administered during the tilt test, 9 of the 11 patients with negative electrophysiologic and tilt tests had syncope, marked slowing of the heart rate, and hypotension. In contrast, isoproterenol was associated with tachycardia and only a slight decline in arterial pressure in the 8 remaining patients with positive electrophysiologic tests and the 18 control subjects, and syncope developed in only 1 of the 8 patients with positive electrophysiologic tests and negative tilt tests (13 percent) and 2 of the 18 control subjects (11 percent). We conclude that an isoproterenol infusion administered in conjunction with the upright-tilt test may be useful for identifying susceptibility to neurally mediated recurrent syncope.

Adolescent↗
PubMed1989

Cellular electrophysiologic effects of dexamethasone sodium phosphate: implications for cardiac stimulation with steroid-eluting electrodes.

Impregnation of implantable cardiac pacemaker electrodes with dexamethasone sodium phosphate dexamethasone) has been associated with reduced energy requirements for both atrial and ventricular stimulation. To determine whether cardiac cellular electrophysiologic effects of dexamethasone could in part account for lower stimulation thresholds, conventional microelectrode recording and stimulation techniques were used to assess both the immediate (acute) effects of dexamethasone (10(-6) and 10(-4) M) in superfused isolated rabbit right atrial and right ventricular preparations, and chronic effects in rabbit right ventricular tissue following 2 weeks of either daily parenteral dexamethasone (5 mg/kg, plasma concentration approximately 1 to 5 x 10(-5) M) or saline placebo injections. In acute superfusion studies, dexamethasone resulted in a concentration dependent prolongation of spontaneous right atrial cycle length, but did not significantly affect right atrial transmembrane action potential characteristics or refractoriness. However, acute dexamethasone superfusion tended to increase right ventricular resting membrane potential and diminish stimulation threshold. On the other hand, compared to findings in saline-injected control rabbits, chronic dexamethasone injection had little effect on right ventricular stimulation threshold transmembrane action potential characteristics, or right ventricular refractoriness. Thus, the acute direct electrophysiologic effects of high-dose dexamethasone are compatible with the early reduction of cardiac stimulation thresholds associated with dexamethasone impregnated pacing electrodes. On the other hand, electrophysiologic findings in the presence of chronic dexamethasone exposure do not fully account for long-term reduction of stimulation energy requirements.

Animals↗
PubMed1989

Cardiac electrophysiologic effects of orally administered DPI 201-106 in conscious canines: effects of pharmacologic autonomic blockade or cardiac transplantation.

This study assessed the cardiac electrophysiologic effects of DPI 201-106 (DPI), a novel orally absorbable positive inotropic agent, the administration of which has been associated with electrocardiographic (ECG) QT and T-wave changes. In the intact conscious dog, oral administration of both 8 and 16 mg/kg DPI produced marked sinus cycle length prolongation (8 mg/kg, + 11%; 16 mg/kg, + 9%) within 60 min of DPI administration (p less than 0.05 vs. baseline). DPI also tended to prolong right atrial refractory periods, and increase sinus node recovery time. In addition, DPI exhibited a negative dromotropic effect on the atrioventricular (AV) node, prolonging both AV node effective and functional refractory periods and tending to increase the minimum atrial paced cycle length at which AV conduction of 1:1 was maintained. DPI also significantly increased right ventricular effective refractory period (ERP) at both doses studied and increased ventricular functional refractory period (FRP) at the 16-mg/kg dose. Finally, although DPI administration was associated with QT interval prolongation, this effect was slight when corrected for sinus cycle length (SCL) (QTc, +3%). When administered concomitantly with propranolol and atropine or after surgical cardiac denervation, DPI-induced electrophysiologic changes were largely attenuated or abolished. Thus, findings in this study indicate that the apparent cardiac electrophysiologic effects of DPI are predominantly of neurally mediated origin in this animal model.

Administration, Oral↗
PubMed1989

Electrophysiological effects of left ventricular free wall traction in intact hearts.

Transmural multipolar electrodes, sonomicrometers implanted within the left ventricular wall, and cardiac electrical stimulation techniques were used to examine the effect of transient mechanically applied traction to the left ventricular free wall on local electrophysiological properties. Twenty-five open-chest dogs were atrially paced (cycle length 400 ms) followed by insertion of timed premature extrastimuli at left ventricular epicardial pacing sites either in the vicinity of (traction zone) or remote from (nontraction-control zone) the site of left ventricular free wall traction. Electrophysiological recordings were made before and during intermittent left ventricular free wall traction applied in late diastole (rate 25 cm/s; duration 170 ms). In 22 of 25 dogs, application of traction resulted in early local ventricular activation (mean activation advancement 64 +/- 15 ms), altered QRS morphology of the last conducted atrial drive train beat, and a relative prolongation of ventricular refractoriness in the traction zone. Conversely, in the nontraction-control zone, early activation did not occur and refractoriness was unchanged. Alterations in regional myocardial blood flow (assessed by microsphere technique) did not appear responsible for the observed changes. Furthermore, phenol interruption of local sympathetic or combined sympathetic and parasympathetic innervation or verapamil pretreatment had no impact on the mechanically induced electrophysiological changes. Thus, in normal myocardium in situ, regional abnormalities in wall motion may be associated with alterations of local ventricular activation and refractoriness, factors that in the diseased heart could lead to increased susceptibility to arrhythmias.

Animals↗
PubMed1987

Single-chamber cardiac pacing with activity-initiated chronotropic response: evaluation by cardiopulmonary exercise testing.

In this study, sequential cardiopulmonary exercise testing was used to assess the physiologic benefits of a single-chamber ventricular pacing system that utilizes a piezoceramic sensor to adjust heart rate by detecting "physical activity." An initial exercise test was conducted with the pacemaker programmed (based on a randomization table) to either the fixed rate (VVI, 70 beats/min) or rate-variable (VVI-Act) mode, and the results were compared with those obtained during a second exercise test in which the pacemaker was programmed to the alternate pacing mode. A 1.5 to 2 hr rest period was permitted between exercise tests, each of which consisted of a symptom-limited constant speed (3.0 mph) Balke protocol with 2 min stages commencing at 0.0% grade with increments of 2.5% at end of each stage. Compared with findings during fixed-rate VVI pacing, VVI-Act pacing was associated with greater exercise-induced positive chronotropic response (mean maximum heart rate VVI-Act 128 +/- 15.3 beats/min vs VVI 90 +/- 28.4 beats/min; p less than .01), prolongation of exercise duration (VVI-Act 10.2 +/- 3.8 min vs VVI 7.7 +/- 2.5 min; p less than .01), increased peak oxygen consumption (VVI-Act 1617 +/- 656 ml O2/min vs VVI 1325 +/- 451 ml O2/min; p less than .01), and onset of anaerobic threshold at a higher oxygen consumption (VVI-Act 1208 +/- 343 ml O2/min vs VVI 1064 +/- 377 ml O2/min: p less than .01). Additionally, of 44 comparable exercise stages tested in the two pacing modes, perceived exertion (assessed by a numerical grading system) was lower in 38 of 44 instances during VVI-Act compared with VVI pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗