Characterizing Hypertension Specialist Care in Canada: A National Survey

Background

The hypertension specialist often receives referrals of patients with young-onset, severe, difficult-to-control hypertension, patients with hypertensive emergencies, and patients with secondary causes of hypertension. Specialist hypertension care compliments primary care for these complex patients and contributes to an overall hypertension control strategy. The objective of this study was to characterize hypertension centres and the practice patterns of Canadian hypertension specialists.

Methods

Adult hypertension specialists across Canada were surveyed to describe hypertension centres and specialist practice in Canada, including the following: the patient population managed by hypertension specialists; details on how care is provided; practice pattern variations; and differences in access to specialized hypertension resources across the country.

Results

The survey response rate was 73.5% from 25 hypertension centres. Most respondents were nephrologists and general internal medicine specialists. Hypertension centres saw between 50 and 2500 patients yearly. A mean of 17% (± 15%) of patients were referred from the emergency department and a mean of 52% (± 24%) were referred from primary care. Most centres had access to specialized testing (adrenal vein sampling, level 1 sleep studies, autonomic testing) and advanced therapies for resistant hypertension (renal denervation). Considerable heterogeneity was present in the target blood pressure in young people with low cardiovascular risk and in the diagnostic algorithms for investigating secondary causes of hypertension.

Conclusions

These results summarize the current state of hypertension specialist care and highlight opportunities for further collaboration among hypertension specialists, including standardization of the approach to specialist care for patients with hypertension.

Unusual sensory variant of Guillain-Barré syndrome

We describe a 52-year-old woman presenting with acute onset of severe burning paraesthesia in the hands and feet associated with allodynia and antalgic gait. At the time of admission to hospital no motor weakness was present. A diagnosis of Guillain-Barré syndrome (GBS) was considered when neurophysiological studies were completed showing convincing evidence of demyelination on motor conduction studies and sural sparing on sensory nerve studies.¹ We describe this case as a sensory variant of GBS. Clinical improvement followed treatment with a single course of intravenous immunoglobulin (IVIG). The patient made a complete clinical recovery within 6 months of onset and repeat neurophysiological studies showed marked improvement. We encourage clinicians to consider an atypical variant of GBS in patients presenting with acute sensory complaints.

Does initiation of HIV antiretroviral therapy influence patterns of syringe lending among injection drug users?

The delivery of antiretroviral therapy (ART) to injection drug users (IDU) may be influenced by provider concerns regarding the potential for increased HIV-related risk behavior following the initiation of HIV treatment. We evaluated whether ART initiation was associated with changes in syringe lending patterns among a long-term prospective cohort of HIV-positive IDU in Vancouver, Canada. Among 380 ART-naïve individuals eligible for this analysis, the median age was 34.2 (interquartile range [IQR] 27.7-40.8), 171 (45.0%) were female, and the median follow-up duration was 60 months (IQR=18-113). Between May 1996 and April 2008, 260 (68.4%) participants initiated ART. In a generalized linear mixed-effects model which compared each individual's likelihood of sharing syringes prior to and following the initiation of ART, syringe lending was not significantly associated with ART initiation in unadjusted (odds ratio=0.72, 95% CI: 0.38-1.36) or adjusted (odds ratio=0.78, 95% CI: 0.42-1.45) analyses. Concerns regarding increased injection risk behaviors following the initiation of ART were not observed in this setting.

Predictors of early hospital readmission in HIV-infected patients with pneumonia

OBJECTIVE

Although hospitalization patterns have been studied, little is known about hospital readmission among HIV-infected patients in the era of highly active antiretroviral therapy. We explored the risk factors for early readmission to a tertiary care inner-city hospital among HIV-infected patients with pneumonia in Vancouver, Canada.

DESIGN

Case-control study.

SETTING

Tertiary care, university-affiliated, inner-city hospital.

PARTICIPANTS

All HIV-infected patients who were hospitalized with Pneumocystis carinii pneumonia (PCP) or bacterial pneumonia (BP) between January 1997 and December 2000. Case patients included those who had early readmissions, defined as being readmitted within 2 weeks of discharge (N = 131). Control patients were randomly selected HIV-infected patients admitted during the study period who were not readmitted within 2 weeks of discharge (N = 131), matched to the cases by proportion of PCP to BP.

MEASUREMENTS

Sociodemographic, HIV risk category, and clinical data were compared using chi2 test for categorical variables, and the Wilcoxon rank-sum test was used for continuous variables. Multivariable logistic regression was performed to determine the factors independently associated with early readmission. We also reviewed the medical records of 132 patients admitted to the HIV/AIDS ward during the study period and collected more detailed clinical data for a subanalysis.

MAIN RESULTS

Patients were at significantly increased odds of early readmission if they left the hospital against medical advice (AMA) (adjusted odds ratio [OR], 4.26; 95% confidence interval [95% CI], 2.13 to 8.55), lived in the poorest urban neighborhood (OR, 2.03; 95% CI, 1.09 to 3.77), were hospitalized in summer season (May though October, OR, 2.36; 95% CI, 1.36 to 4.10), or had been admitted in the preceding 6 months (OR, 2.55; 95% CI, 1.46 to 4.47). Gender, age, history of AIDS-defining illness, and injection drug use status were not significantly associated with early readmission.

CONCLUSIONS

Predictors of early readmission of HIV-infected patients with pneumonia included: leaving hospital AMA, living in the poorest urban neighborhood, being hospitalized in the preceding 6 months and during the summer months. Interventions involving social work may address some of the underlying reasons why these patients leave hospital AMA and should be further studied.

Solution structure of bound trimethoprim in its complex with Lactobacillus casei dihydrofolate reductase

Two- and three-dimensional (2D and 3D) NMR techniques have been used to assign the signals from nearly all of the protons in Lactobacillus casei dihydrofolate reductase (DHFR) (M(r) 18,300) in its 1:1 complex with the antibacterial drug trimethoprim. A sample of uniformly 15N-labeled protein was examined using 3D 15N/1H experiments [nuclear Overhauser, heteronuclear multiple quantum coherence (NOESY-HMQC) and total correlation, heteronuclear multiple quantum coherence (TOCSY-HMQC) experiments]. Twenty-two intermolecular NOEs between trimethoprim and protein protons and four intramolecular NOEs in the ligand have been detected. Some were obtained by using heteronuclear editing and 2D HMQC-NOESY experiments on complexes formed with 15N-and 13C-labeled trimethoprim molecules ([1,3-15N2,2-amino-15N]-and [7-13C,4'-methoxy-13C]trimethoprim) bound to unlabeled protein. The ligand-protein NOEs were used as distance constraints in conjunction with minimum energy and simulated annealing calculations (carried out with X-PLOR) to dock the trimethoprim ligand into dihydrofolate reductase, using as a starting structure the crystal coordinates from a related complex with a similar overall protein structure. The restrained minimum energy calculations and the simulated annealing calculations gave 83 calculated structures with distance violations of < 0.1 A. In all of these, the two aromatic rings of trimethoprim occupied essentially the same region of conformational space in the binding site (RMSD = 0.63 A). The protein residues nearest to the bound trimethoprim were found to be very similar in all of the structures and agreed well with corresponding contact residues observed in the X-ray crystal studies on trimethoprim complexes formed with Escherichia coli and chicken liver DHFRs.

1H and 15N NMR studies of protonation and hydrogen-bonding in the binding of trimethoprim to dihydrofolate reductase

The binding of trimethoprim and [1,3,2-amino-15N3]-trimethoprim to Lactobacillus casei dihydrofolate reductase has been studied by 15N and 1H NMR spectroscopy. 15N NMR spectra of the bound drug were obtained by using polarisation transfer pulse sequences. The 15N chemical shifts and 1H-15N spin-coupling constants show unambiguously that the drug is protonated on N1 when bound to the enzyme. The N1-proton resonance in the complex has been assigned using the 15N-enriched molecule. The temperature-dependence of the linewidth of this resonance has been used to estimate the rate of exchange of this proton with the solvent: 160 +/- 10 S-1 at 313 K, with an activation energy of 75 (+/-9) kJ X mole-1. This is considerably faster than the dissociation rate of the drug from this complex, demonstrating that there are local fluctuations in the structure of the complex.

Effect of a single amino acid substitution on Escherichia coli dihydrofolate reductase catalysis and ligand binding

The two isozymes of dihydrofolate reductase (Forms 1 and 2) from, a Trimethoprim-resistant strain of Escherichia coli (RT500) were separated and purified to homogeneity using a simple procedure based on differential elution from a Methotrexate affinity column. The complete amino acid sequence of the Form 2 isozyme was determined, and it differs from that of Form 1 in only one position. Residue 28 is arginine in Form 2 and leucine in Form 1. However, the isozymes differ greatly in their binding and kinetic properties. Equilibrium dialysis studies showed the Trimethoprim dissociation constants of Form 2 are about 50-fold greater than those of Form 1 in both the binary complex and the ternary complex with NADPH. Similarly, the Methotrexate dissociation constant of Form 2 is about 10-fold greater than that of Form 1. The two isozymes also differ in their turnover numbers at pH 7 (Form 1 is 10-fold more active) and inhibition by divalent cations. Form 1 is extremely sensitive to BaCl2 (50% inhibition at 0.5 mM), whereas Form 2 is much less sensitive (50% inhibition at 60 mM). In the presence of 10 mM BaCl2, Form 1 has the functional characteristics of Form 2. Its turnover number is decreased, its Trimethoprim Ki is increased, and the shape of its pH-activity profile is identical with that of Form 2. The x-ray structures and amino acid sequences of several bacterial dihydrofolate reductases indicate that Asp-27 is important in inhibitor binding and may be involved in catalysis. The present data provide kinetic evidence for this hypothesis, and it is proposed that almost all the unusual characteristics of Form 2 are the direct result of a charge interaction between Arg-28 and Asp-27. A similar interaction between Ba2+ and the Asp-27 of Form 1 can result in an enzyme complex that is kinetically similar to Form 2.