Michael G. Kienzle

Sympathoinhibitory responses to digitalis glycosides in heart failure patients. Direct evidence from sympathetic neural recordings.

Digitalis glycosides exert both excitatory and inhibitory autonomic actions in animals and produce vasoconstriction in normal humans but produce vasodilation in heart failure patients. To determine whether or not these contrasting vascular responses are due to differing autonomic actions of the drug, we compared the responses to intravenous administration of Cedilanid-D (0.02 mg/kg) in eight normal subjects (mean age, 23 +/- 1 years) and eight patients with moderate-to-severe heart failure (mean age, 52 +/- 5 years, NYHA Class III-IV). Hemodynamics and efferent sympathetic nerve activity to muscle (MSNA) were measured during 5-minute periods before (control) and 20 minutes after drug administration. In the heart failure patients, Cedilanid-D significantly increased systolic and pulse pressures, whereas mean arterial pressure was unchanged. There was a decrease in right atrial pressure and a tendency for a decrease in pulmonary artery diastolic pressure with a slowing of heart rate. Cardiac index increased by 24 +/- 7%. Short-term administration of digitalis in these heart failure patients produced a fall in forearm vascular resistance (from 37.6 +/- 8.2 to 31.8 +/- 8.1 units, p less than 0.05) and an early, profound, and sustained decrease in MSNA (from 831.0 +/- 118.4 to 474.4 +/- 103.6 units/100 heart beats, p less than 0.01). Digitalis glycosides produced different vascular and MSNA responses in the normal subjects. In the normal volunteers, the drug significantly increased systolic, mean, and pulse pressures and decreased central venous pressure and heart rate. Despite the significant increase in arterial pressure, there was no change in forearm vascular resistance (from 11.7 +/- 1.0 to 12.7 +/- 1.0 units, p = NS) or MSNA (from 494.8 +/- 88.5 to 369.1 +/- 60.5 units/100 heart beats, p = NS), suggesting a sympathoexcitatory response in normal subjects. To determine whether or not the digitalis-induced sympathoinhibition in the heart failure patients was simply due to an inotropic effect (stimulation of inhibitory cardiac mechanoreceptors), we studied the responses of seven additional patients with heart failure before and during administration of dobutamine (3.4 +/- 0.4 micrograms/kg/min). Dobutamine produced a 34 +/- 3% increase in cardiac index, no significant change in systemic arterial pressures, a decrease in pulmonary artery diastolic and right atrial pressures, and no change in heart rate or forearm vascular resistance (from 30.2 +/- 4.3 to 26.5 +/- 4.7 units, p = NS).(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical, hemodynamic and sympathetic neural correlates of heart rate variability in congestive heart failure

Heart rate (HR) variability has long been recognized as a sign of cardiac health. In the presence of heart disease, HR variability decreases, an observation that has been associated with poor prognosis in a number of recent studies. HR variability is particularly altered in congestive heart failure (CHF), a condition associated with a number of typical functional hemodynamic and neurohumoral alterations. The relation of measurements of HR variability to these abnormalities in patients with heart failure has not been carefully examined. Twenty-three patients (19 men, 4 women, mean age 49 years) with New York Heart Association class II to IV CHF were studied prospectively without cardiac medications; radionuclide ventriculography, right-sided heart catheterization, peroneal microneurography, plasma norepinephrine and 24- to 48-hour ambulatory electrocardiography were performed. Average RR interval and its standard deviation, and HR power spectrum (0 to 0.5, 0.05 to 0.15 and 0.2 to 0.5 Hz) were derived from the ambulatory electrocardiographic recordings and compared with left ventricular ejection fraction, thermodilution cardiac output, pulmonary arterial wedge pressure, New York Heart Association class, age, muscle sympathetic nerve activity (peroneal nerve) and norepinephrine level by linear regression. None of the measures of HR variability were significantly related to age, left ventricular ejection fraction, cardiac output or functional classification, whereas the 0.05 to 0.15 and 0.20 to 0.50 Hz components were weakly but significantly related to cardiac output (r = 0.49 and 0.42, p = 0.02 and 0.045, respectively). In contrast, a generally stronger and negative relation was demonstrated between spectral and nonspectral measurements of HR variability, and indicators of sympathoexcitation, muscle sympathetic nerve activity and plasma norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy, current, and success in defibrillation and cardioversion: clinical studies using an automated impedance-based method of energy adjustment.

The purposes of this study were two. First, we wanted to evaluate in patients a technique for automated adjustment of selected energy for defibrillation or cardioversion based on transthoracic impedance. Second, we wanted to define the relationship of peak current and shock success in various arrhythmias. Applying a previously validated method of predicting transthoracic impedance in advance of any shock, we modified defibrillators to automatically double the operator-selected energy if the predicted impedance exceeded 70 omega. Success rates of shocks given for ventricular and atrial arrhythmias from these modified energy-adjusting defibrillators were compared with success rates for shocks given from standard defibrillators. We prospectively collected data on 347 patients who received a total of 1009 shocks. Low-energy (100 J) shocks given to high-impedance (greater than or equal to 70 omega) patients had a poor success rate; in such high-impedance patients significant improvement in shock success rate was achieved by the energy-adjusting defibrillators. For example, when 100 J shocks were selected for high-impedance patients in ventricular fibrillation the energy-adjusting defibrillators achieved a shock success rate of 75%, whereas standard defibrillators achieved a shock success rate of only 36% (p less than .01). Similar improvements were seen for ventricular tachycardia and atrial fibrillation. Thus, automated energy adjustment based on transthoracic impedance is a beneficial approach to defibrillation and cardioversion. For ventricular fibrillation, atrial fibrillation, and atrial flutter there was a clear relationship between peak current and shock success.(ABSTRACT TRUNCATED AT 250 WORDS)

Severe cardiomyopathy due to chronic rapidly conducted atrial fibrillation: complete recovery after restoration of sinus rhythm

T he effect of chronic tachycardia on cardiac function is controversial. However, previous reports suggest that chronic atrial tachyarrhythmias can produce or facilitate development of reversible congestive heart failure in the absence of significant underlying myocardial disease [1,2]. The majority of the patients previously described have had automatic or reentrant supraventricular tachycardia that was present at birth Qr developed later in childhood. We report the case of an adult patient with chronic rapidly conducting atrial fibrillation and severe congestive cardiomyopathy that was completely reversed after antiarrhythmic therapy restored normal sinus rhythm.

Ventricular tachycardia rate and morphology determine energy and current requirements for transthoracic cardioversion.

BackgroundThe electrical current and energy required to terminate ventricular tachyarrhythmias are known to vary by arrhythmia: Ventricular tachycardia (VT) is generally considered to require less energy than ventricular fibrillation (VF). The hypothesis of our study was that current requirements for transthoracic termination of VT are further determined by VT rate and QRS complex morphology. Methods and ResultsWe prospectively studied 203 patients who received a total of 569 shocks for VT or VF by following a current-based protocol. This protocol recommended shocks for VT beginning at 18 A (70±22 J) and shocks for VF beginning at 25 or 30 A (13752 J or 221±70 J). The ventricular tachyarrhythmias were subclassified as monomorphic VT (MVT): uniform QRS complex morphology on surface electrocardiogram and heart rate >100 beats per minute; polymorphic VT (PVT): nonuniform QRS complex morphology and heart rate ≤300 beats per minute; or VF: nonuniform QRS complex morphology and heart rate >300 beats per minute. We found that shocks of 18 A and 25 A for terminating MIVT had success rates of 69% and 82%, respectively, whereas such low-current shocks were less successful for PVT (33% at 18 A) and for VF (19% at 18 A, 53% at 25 A). High-current shocks of 35 A and 40 A were equally successful for the three ventricular tachyarrhythmias. Subdividing MVT revealed that slower MVT (heart rate < 200 beats per minute) had a significantly better success rate with low-current shocks of 18 A and 25 A than did faster MVT (>200 beats per minute) (89% versus 72% success, p < 0.01). Bundle branch block morphology, QRS axis, and duration of ventricular tachyarrhythmia did not alter current requirements. ConclusionsHeart rate and electrocardiographic degree of organization of ventricular tachycardia are important determinants of transthoracic energy and current requirements for cardioversion and defibrillation. Transthoracic termination of MVT requires relatively low current or energy, but PVT behaves more like VF and requires higher electrical current or energy.

Tele-Education in a Telemedicine Environment: Implications for Rural Health Care and Academic Medical Centers

Over 50 million people in the United States (about 20% of the population) live in rural areas, but only 9% of the nations physicians practice in rural communities. It is difficult to recruit and retain rural health care practitioners, partly because of issues relating to professional isolation. New and enhanced telecommunications links between community and academic hospitals show promise for reducing this isolation and enhancing lifelong learning opportunities for rural health care providers. This paper will explore some of the issues involved in using interactive video (telemedicine) networks to transmit continuing medical education programming from an academic center to multiple rural hospitals. Data from a recent University of Iowa survey of the states health educators will be presented as one approach to assessing the health care marketplace for the deployment of tele-education services.

Muscle Sympathetic Nerve Activity Is Reduced in IDDM Before Overt Autonomic Neuropathy

Studies of heart-rate variability have demonstrated that abnormal cardiac parasympathetic activity in individuals with IDDM precedes the development of other signs or symptoms of diabetic autonomic neuropathy. To determine whether IDDM patients have impaired sympathetic activity compared with normal control subjects before the onset of overt neuropathy, we directly recorded MSNA. We also examined the effects of changes in plasma glucose and insulin on sympathetic function in each group. MSNA was recorded by using microneurographic techniques in 10 IDDM patients without clinically evident diabetic complications and 10 control subjects. MSNA was compared during a 15-min fasting baseline period and during insulin infusion (120 mU · m−2 · min−1) with 30 min of euglycemia. A cold pressor test was performed at the end of euglycemia. Power spectral analysis of 24-h RR variability was used to assess cardiac autonomic function. IDDM patients had lower MSNA than control subjects at baseline (8 ± 1 vs. 18 ± 3 burst/min, P < 0.02). MSNA increased in both groups with insulin infusion (P < 0.01) but remained lower in IDDM patients (20 ± 3 vs. 28 ± 3 burst/min, P < 0.01). In the IDDM group, we found no relationships between MSNA and plasma glucose, insulin, or HbA1c concentrations. BP levels did not differ at rest or during insulin. Heart-rate variability and the MSNA response to cold pressor testing in IDDM patients did not differ from those in healthy control subjects. IDDM patients had reduced MSNA at rest and in response to insulin. The lower MSNA is not attributable to differences in plasma glucose or insulin, but, rather, is most likely an early manifestation of diabetic autonomic neuropathy that precedes impaired cardiac parasympathetic control.

Induced Sustained Ventricular Tachycardia in Nonischemic Dilated Cardiomyopathy: Dependence on Clinical Presentation and Response to Antiarrhythmic Agents

Thirty‐one patients with nonischemic dilated cardiomyopathy either idiopathic or due to regurgitant valvular disease were studied in the cardiac electrophysiology lab. The indications for study were sustained ventricular tachycardia (VT) in 26, ventricular fibrillation (VF) in 11, and syncope of unknown etiology in 4. Sustained VT was reproducibly induced in 17 patients, including 12 with a history of sustained VT, 2 with VF and 3 with syncope. Of 15 patients undergoing serial antiarrhythmic drug studies, sustained VT was rendered noninducible or nonsustained in 23. Three had recurrent arrhythmic events while on therapy predicted to be effective. One of 2 patients discharged on a regimen predicted to be ineffective had a recurrence of sustained VT that resulted in cardiac arrest. Of 14 patients in whom sustained VT could not he reproducibly induced, 2 subsequently had spontaneous occurrences of sustained VT, and 2 experienced aborted sudden death. These results suggest the following; (1) the induction of sustained VT in the setting of nonischemic dilated cardiomyopathy is dependent on the clinical presentation; (2) antiarrhythmic drugs frequently render sustained VT noninducible or nonsustained; (3) antiarrhythmic drug suppression of inducible sustained VT predicts long‐term prevention of spontaneous recurrences; and (4) noninducibility of sustained VT in the baseline state does not predict freedom from subsequent episodes of VT or sudden death.

Telemedicine to Iowa’s Correctional Facilities: Initial Clinical Experience and Assessment of Program Costs

OBJECTIVEnTo evaluate the costs and benefits of a prison telemedicine program for the institutions involved and to assess early provider satisfaction.nnnMATERIALS AND METHODSnA survey of primary care and consulting providers from four prisons and an academic tertiary care facility in Iowa was conducted during the first year of telemedicine service linked with the states correctional facilities, from March, 1997 to February, 1998. Data were evaluated from 247 completed telemedicine encounters. Cost estimates were made for (1) 1997 cost data for the 4,396 Iowa prisoners who were transported to The University of Iowa Hospitals and Clinics (UIHC) for their health care, and (2) the equipment, circuitry, and personnel costs necessary on both ends of the network to provide comparable telemedicine service to remote patients and providers. A formula for estimating the cost of implementing a telemedicine service is presented. It includes a projection for determining at what point the cost of the telemedicine visit approaches the average cost of an on-site visit (breakeven point). There was also a brief survey administered to presenting and consulting physicians to determine their overall satisfaction with the telemedicine system for diagnosis, treatment planning, and follow-up.nnnRESULTSnThe average cost to the prisons for an on-site inmate visit to the University of Iowa Hospitals and Clinics (UIHC) was

Problems in measuring heart rate variability of patients with congestive heart failure

115 during our study period, from March 1997 to February 1998. Using a formula that specifies a number of fixed and variable costs for implementing telemedicine, we were able to determine that the breakeven point for Iowas correctional facilities would require 275 teleconsultations per year, per site (total of 1,575 consultations a year). Given the higher equipment investment at the UIHC hub, the breakeven point would be around 2,000 teleconsultations annually. Cost studies did not include medical care, which is assumed to be relatively comparable for both on-site and telemedicine interactions. Overall, referring physicians expressed a higher rate of satisfaction with telemedicine than specialists (4.19 to 3.45, respectively, on a scale of 1 to 5 - 5 representing the highest ranking). Both consulting and referring physicians ranked the quality of transmission the highest among all questions regarding satisfaction with the telemedicine system.nnnCONCLUSIONSnNo one should anticipate instantaneous cost-effectiveness with telemedicine. However, with careful planning, implementing a telemedicine program can be cost-acceptable initially. Telemedicine ultimately becomes cost-effective as the volume of teleconsults increases.