William P. Santamore

Kinematics of the Beating Heart

We introduce a new approach to the quantification of myocardial strain. It utilizes the theoretical frame work of kinematics and can thus account for the large time-varying displacements present in the intact beating heart. For arbitrary small segments of myocardium, we show how these displacements can be described completely by a rotation tensor and a stretch tensor. We demonstrate the physiologic meaning of this analysis in an anesthetized dog. An epicardial region was seen to exhibit a local twist quantified by the rotation tensor and a segmental shortening quantified by the stretch tensor.

Altered coronary flow responses to vasoactive drugs in the presence of coronary arterial stenosis in the dog.

Abstract Recent in vitro observations of human coronary arteries have suggested that intraluminal pressure can be a determinant of the resistance to flow through the stenosis. This study examined whether similar pressure-dependent changes in stenotic resistance could be observed and analyzed in an open chest, anesthetized, animal model of coronary arterial stenosis. Without stenosis, intracoronary isoproterenol (1 μg) or nitroglycerin (10 μg) increased flow and decreased coronary resistance, whereas methoxamine (500 μg) or vasopressin (0.2 U) decreased flow and increased coronary resistance. After partial arterial constriction, administration of isoproterenol (1 μg) resulted in a decrease in coronary pressure from 61.2 ± 2.5 to 39.4 ± 2.7 mm Hg (p ≤ 0.05), a 23 percent derease in distal coronary resistance (p ≤ 0.05) and a 22 percent decrease in flow associated with an increase in stenotic resistance of 2.34 ± 0.97 (p ≤ 0.05). Similarly, nitroglycerin caused a decrease in coronary pressure from 55.7 ± 3.1 to 42.1 ± 3.6 mm Hg (p ≤ 0.05), a 29 percent increase in distal coronary resistance and only a 1 percent increase in flow associated with a 38 percent increase in stenotic resistance. Methoxamine caused an increase in coronary pressure from 62.8 ± 2.0 to 73.6 ± 3.4 mm Hg (p ≤ 0.05), an 18 percent increase in distal coronary resistance, an 8 percent decrease in flow and a 10 percent decrease in stenotic resistance. Vasopressin caused an increase in coronary pressure from 61.0 ± 1.5 to 99.2 ± 7.1 mm Hg (p ≤ 0.05), a 239 percent increase in distal coronary resistance but only a 45 percent decrease in flow associated with a decrease in stenotic resistance of 1.33 ± 0.91 (p ≤ 0.05). Passive changes in the stenotic area caused by coronary pressure changes are postulated as part of the mechanism for the observed changes in stenotic resistance. This hypothesis is strengthened by the changes in stenotic resistance and radiographic analysis obtained from an in vitro carotid arterial preparation. The pressure-dependency of stenotic resistance could be an additional factor in the treatment of patients with coronary artery disease.

Managing Heart Failure Care Using an Internet-Based Telemedicine System

BACKGROUNDnManaging patients with heart failure (HF) is labor intensive, and follow-up is often inadequate to detect day-to-day changes that ultimately lead to decompensation. We tested the effect of an Internet-based telemedicine (T) system that provides frequent surveillance and increased communicate between HF patients and their provider on frequency of hospitalization in a cohort of patients with advanced HF.nnnMETHODS AND RESULTSnHF patients in NYHA Class II-IV were randomized to usual care (UC, n = 24) or T (T plus UC, n = 24) and followed for 1 year. Office visits, emergency department visits, hospitalizations, telephone calls, and number of Internet communications were measured over the 1-year period. Left ventricular ejection fraction (EF) was assessed by echocardiography in both groups. For T, mean age was 53.2 +/- 2.0 years (72% male, 61% Caucasian, 39% African American). For UC, mean age was 54.1 +/- 2.6 years (76% male, 72% Caucasian, 14% African American, and 14% Hispanic). HF etiologies and EF were similar in both groups. During the 12-month period, UC had 74 total phone calls to the practice, whereas T had 88 telephone calls plus 1887 telemedicine data messages (6.5 messages/patient/month). ER visits were lower in the T group (T 5, UC 12; P < .05). Hospital admissions (T 24, C 40; P = .025) and total hospital days (T 84, UC 226 days; P < .005) were lower in T. Unscheduled clinic visits (T 13, UC 13; P = NS) and scheduled clinic visits (T 78, UC 94; P = NS) were similar in both groups.nnnCONCLUSIONSnFrequent monitoring and patient management using a telemedicine system may help to reduce hospitalizations, hospital days, and emergency department visits.

Impact of a Telemedicine System with Automated Reminders on Outcomes in Women with Gestational Diabetes Mellitus

BACKGROUNDnHealth information technology has been proven to be a successful tool for the management of patients with multiple medical conditions. The purpose of this study was to examine the impact of an enhanced telemedicine system on glucose control and pregnancy outcomes in women with gestational diabetes mellitus (GDM).nnnSUBJECTS AND METHODSnWe used an Internet-based telemedicine system to also allow interactive voice response phone communication between patients and providers and to provide automated reminders to transmit data. Women with GDM were randomized to either the telemedicine group (n=40) or the control group (n=40) and asked to monitor their blood glucose levels four times a day. Women in the intervention group transmitted those values via the telemedicine system, whereas women in the control group maintained paper logbooks, which were reviewed at prenatal visits. Primary outcomes were infant birth weight and maternal glucose control. Data collection included blood glucose records, transmission rates for the intervention group, and chart review.nnnRESULTSnThere were no significant differences between the two groups (telemedicine vs. controls) in regard to maternal blood glucose values or infant birth weight. However, adding telephone access and reminders increased transmission rates of data in the intervention group compared with the intervention group in our previous study (35.6±32.3 sets of data vs.17.4±16.9 sets of data; P<0.01).nnnCONCLUSIONSnOur enhanced telemedicine monitoring system increased system utilization and contact between women with GDM and their healthcare providers but did not impact upon pregnancy outcomes.

Reducing cardiovascular disease risk in medically underserved urban and rural communities

OBJECTIVESnThe aim of this study is to evaluate methods for lowering cardiovascular disease (CVD) risk in asymptomatic urban and rural underserved subjects.nnnBACKGROUNDnMedically underserved populations are at increased CVD risk, and systems to lower CVD risk are needed. Nurse management (NM) and telemedicine (T) systems may provide low-cost solutions for this care.nnnMETHODSnWe randomized 465 subjects without overt CVD, with Framingham CVD risk >10% to NM with 4 visits over 1 year, or NM plus T to facilitate weight, blood pressure (BP), and physical activity reporting. The study goal was to reduce CVD risk by 5%.nnnRESULTSnThree hundred eighty-eight subjects completed the study. Cardiovascular disease risk fell by ≥ 5% in 32% of the NM group and 26% of the T group (P, nonsignificant). In hyperlipidemic subjects, total cholesterol decreased (NM -21.9 ± 39.4, T -22.7 ± 41.3 mg/dL) significantly. In subjects with grade II hypertension (systolic BP ≥ 160 mm Hg, 24% of subjects), both NM and T groups had a similar BP response (average study BP: NM 147.4 ± 17.5, T 145.3. ± 18.4, P is nonsignificant), and for those with grade I hypertension (37% of subjects), T had a lower average study BP compared to NM (NM 140.4 ± 16.9, T 134.6 ± 15.0, P = .058). In subjects at high risk (Framingham score ≥ 20%), risk fell 6.0% ± 9.9%; in subjects at intermediate risk (Framingham score ≥ 10, < 20), risk fell 1.3% ± 4.5% (P < .001 compared to high-risk subjects). Medication adherence was similar in both high- and intermediate-risk subjects.nnnCONCLUSIONSnIn 2 underserved populations, CVD risk was reduced by a nurse intervention; T did not add to the risk improvement. Reductions in BP and blood lipids occurred in both high- and intermediate-risk subjects with greatest reductions noted in the high-risk subjects. Frequent communication using a nurse intervention contributes to improved CVD risk in asymptomatic, underserved subjects with increased CVD risk. Telemedicine did not change the effectiveness of the nurse intervention.

Managing hypertension in urban underserved subjects using telemedicine--a clinical trial.

BACKGROUNDnWe evaluated an Internet- and telephone-based telemedicine system for reducing blood pressure (BP) in underserved subjects with hypertension.nnnMETHODSnA total of 241 patients with systolic BP ≥140 mm Hg were randomized to usual care (C; n = 121) or telemedicine (T; n = 120). The T group reported BP, heart rate, weight, steps/day, and tobacco use twice weekly. The primary outcome was BP control at 6 months.nnnRESULTSnAverage age was 59.6 years, average body mass index was 33.7 kg/m(2), 79% were female, 81% were African American, 15% were white, 53% were at or below the federal poverty level, 18% were smokers, and 32% had diabetes. Six-month follow-up was achieved in 206 subjects (C: 107, T: 99). Goal BP was achieved in 52.3% in C and 54.5% in T (P = .43). Systolic BP change (C: -13.9 mm Hg, T: -18.2; P = .118) was similar in both groups. Subjects in the T group reported BP 7.7 ± 6.9 d/mo. Results were not affected by age, sex, ethnicity, education, or income. In nondiabetic T subjects, goal BP was achieved in 58.2% compared with 45.2% of diabetic T subjects (P = .024). Nondiabetic T subjects demonstrated a greater reduction in systolic BP (T: -19 ± 20 mm Hg, C: -12 ± 19 mm Hg; P = .037). No difference in BP response between C and T was noted in patients with diabetes.nnnCONCLUSIONnIn hypertensive subjects, engagement in a system of care with or without telemedicine resulted in significant BP reduction. Telemedicine for nondiabetic patients resulted in a greater reduction in systolic BP compared with usual care. Telemedicine may be a useful tool for managing hypertension particularly among nondiabetic subjects.

CardioClasp: a new passive device to reshape cardiac enlargement.

In dilated heart failure, geometric distortions place an extra load on the myocardial cells. If this extra burden can be eliminated, the myocardial wall stress would decrease leading to improved systolic ventricular performance. In a dilated heart failure model, we wanted to see whether the CardioClasp™ (which uses two indenting bars to reshape the left ventricle [LV] as two widely communicating “lobes” of reduced radius) could improve systolic performance by passively reshaping the LV and reducing the wall stress.In mongrel dogs (n = 7; 25–27 kg), rapid ventricular pacing (210 ppm 1st week to 240 ppm 4th week) induced dilated heart failure. After 4 weeks, LV performance was evaluated at baseline and with the CardioClasp™ by measuring LV end-diastolic and peak LV systolic pressure, LV +dP/dt, LV −dP/dt, and cardiac output. With the Clasp on, LV wall stress was reduced to 58.6 ± 3.5 from 108.3 ± 8.2 g/cm2. The fractional area of contraction (FAC) with the Clasp on (28.4 ± 4.4) was significantly increased (p < 0.05) from baseline (20.8 ± 4.6) and consistent with improved systolic performance. Cardiac output, LV peak systolic and end-diastolic pressures, and regional myocardial blood flow were unaltered.The Clasp was able to acutely reshape the left ventricle, while preserving the contractile mass, and reduced the tension on the myocardial cells and increased the fractional area of contraction without decreasing the systolic blood pressure.

The effects of vasoconstriction on experimental coronary artery stenosis

In summary, we have examined the response to arterial vasoconstriction in an in vitro coronary artery preparation. Without a preexisting stenosis, arterial vasoconstriction had minimal hemodynamic effects. Similarly, with a stenosis created by a circumferential snare, arterial vasoconstriction had minimal hemodynamic effects. In striking contrast, with a stenosis created by intraluminal obstruction, arterial vasoconstriction dramatically increased the hemodyamic severity of the stenosis. The use of an intraluminal obstruction provides a useful animal model for examining hemodynamics in coronary artery disease and had provided some insight into the effects of vasoconstriction on coronary artery hemodynamics. Obviously, this is an experimental study, and care must be taken in extrapolating these results to diseased human coronary arteries.

Elevated collagen content in volume overload induced cardiac hypertrophy.

This investigation was designed to determine if chronic volume overload is associated with altered collagen content of five regions of the myocardium. Five adult cats were subjected to a 6-week period of chronic volume overload induced by atrial septotomy and five untreated animals served as controls. Significant (P < 0.05) right ventricular hypertrophy was present as indicated by the right ventricular body weight ratio. For control animals this ratio was 0.68 ± 0.04 g/kg; for volume overloaded animals it was 0.83 ± 0.05 g/kg.) The collagen content was assessed by measuring the hydroxyproline content of the dried cardiac muscle. Right ventricular endocardium hydroxyproline in volume overloaded animals was significantly elevated above that in control animals (in the latter it was 5.30 ± 0.36 μg/mg; in the former it was 6.33 ± 0.18 μg/mg) while the epicardial collagen content was unchanged. Similarly, the amount of collagen found in the left ventricle was significantly increased in the endocardium and normal in the epicardium. Septal collagen concentration was unaltered in volume overloaded animals. This study demonstrated that alterations in cardiac muscle collagen concentration are associated with volume overload and that these cellular changes are nonuniform.

Early and late results of left ventricular reshaping by passive cardiac-support device in canine heart failure.

BACKGROUNDnWe tested whether the CardioClasp, a passive non-blood-contacting device could decrease excessive geometric burden in dilated cardiomyopathy and improve left ventricular systolic function and contractility by reshaping the left ventricle (LV) and by decreasing LV wall stress (LVWS) without decreasing arterial blood pressure.nnnMETHODSnIn mongrel dogs (n = 6, the early group; n = 6, the chronic group; 25-27 kg), 4 weeks of rapid right ventricular pacing (210 to 240 bpm) induced dilated cardiomyopathy with heart failure. In the early group, we used hemodynamic data and echocardiography to evaluate LV systolic function immediately after placing the CardioClasp device. In the chronic group, we also evaluated LV systolic function immediately after placing the device on dilated hearts and then left the device in place for 30 days. At the end of 30 days, before explantation of the device, we again assessed LV systolic function. We measured fractional area of contraction (FAC), LVWS, and hemodynamic data in both groups.nnnRESULTSnIn the early group, use of the CardioClasp device decreased the LV end-diastolic anterior-to-posterior dimension by 27.8% +/- 2.6% at implantation (p < 0.05). In the chronic group, use of the CardioClasp decreased the LV end-diastolic anterior-to-posterior dimension by 19.4% +/- 2.0% at implantation (p < 0.05) and by 22.0% +/- 3.10% at explantation (p < 0.05). Use of the CardioClasp did not alter LV end-diastolic and peak pressure, LV dP/dts, or cardiac output at implantation or at explantation. In the early group, use of the CardioClasp decreased the LVWS by 43.4% +/- 3.1% at implantation (p < 0.05). In the chronic group, LVWS decreased by 28.8% +/- 2.1% at implantation (p < 0.05) and by 43.3% +/- 5.2% at explantation (p < 0.05). In the early group, FAC increased significantly, by 28.9% +/- 7.8% at implantation (p < 0.05). In the chronic group, FAC increased significantly, by 18% +/- 12% at implantation (p < 0.05) and by 19% +/- 12% at explantation (p < 0.05).nnnCONCLUSIONSnAs expected, use of the CardioClasp device increased FAC and decreased LVWS by reshaping the LV. Use of the CardioClasp device maintained cardiac output and arterial pressure. In 30-day experiments, the increased FAC and decreased LVWS were maintained at explantation.