Better Blood Pressure Control with Impedance Cardiography

Better Blood Pressure Control with Impedance Cardiography

Author: Jeffrey C. Jones M.D.

Problem

Hypertension (HTN) affects 73.6 million people age 20 years or older,¹ and is the leading reason for physician office visits in the United States.²  Only approximately one third of adults with hypertension have their blood pressure under control by JNC-VII guidelines.

Physicians treat HTN using medications that directly affect the two hemodynamic components of blood pressure, systemic vascular resistance (SVR) and cardiac output (CO), and by using diuretics, which reduce pre-load, indirectly reducing cardiac output by reducing stroke volume. Unfortunately, most physicians do not have a non-invasive and quick method to objectively measure the hemodynamic components of a patient’s blood pressure.  As a result, most HTN medications are chosen on a trial and error basis, rather than on knowledge of hemodynamic need. Physicians should be aware of options available to assess their patients’ hemodynamic parameters at the bedside, and thus be able to individualize HTN therapy based on each patient’s hemodynamic status.

Impedance Cardiography

Impedance Cardiography (ICG) is a 5 minute, non-invasive test that uses four sets of electrode sensors on the neck and chest to provide a patient’s current hemodynamic measurements. Changes in impedance occur as the blood volume increases or decreases through dilatation of the aorta with each heartbeat. The beat-to-beat change in impedance is used to determine Cardiac Output (CO/CI) and Systemic Vascular Resistance (SVR/SVRI). Baseline and follow-up ICG can trend a patient’s Thoracic Fluid Content (TFC). Having these measurements at the bedside allows the physician to accurately and confidently determine the best therapeutic choice for each patient’s uncontrolled blood pressure. A patient with a high Cardiac Output (CO/CI) would respond best to a beta blocker. A patient with a high Systemic Vascular Resistance (SVR/SVRI) would respond best to a vasodilator. A patient with rising Thoracic Fluid Content (TFC) would need a diuretic, or increase in current diuretic dose.

Hypertension Study Results with ICG

Two independent, randomized controlled trials have been published reporting statistically significant improvement in HTN control rates when physicians used hemodynamic values provided by ICG to direct HTN therapy as compared to standard physician care alone.

The first study was conducted by the Mayo Clinic. The certified hypertension specialists followed 104 resistant HTN patients (> 2 anti-hypertensive medications) for three months.  Results indicated that the use of ICG guided antihypertensive therapy led to a 70% greater BP control to <140/90mm Hg (56% vs. 33%) when compared to standard care.³

The second study, Consideration of Noninvasive hemodynamic monitoring to Target Reduction of blood pressure Levels (CONTROL), followed 164 uncontrolled HTN patients treated with one or more anti-hypertensive medications. Patients were followed for three months. ICG guided care consisted of medical therapy based on underlying hemodynamics, and resulted in 35% improvement in BP control to <140/90mm Hg vs. Standard Care (77% vs. 55%), and 104% improvement to a more aggressive BP control level of <130/85mm Hg (53% vs. 27%).⁴

Case Study⁵

An example of applying the clinical application of ICG in the drug resistant hypertensive patient is demonstrated in the following case study.

Patient:  67 year old female

History:  HTN for 1 year; recent levels up to 205/105 mm Hg at home

Current Therapy:  Atenolol 100 mg qd, Triameterene/HCTZ 50/12.5 daily; Doxazosin 8 mg/day; Lisinopril 20 mg daily, Clonidine 0.1 mg as needed

ICG Analysis: Extreme elevation of SVRI with low normal TFC, low CI

Treatment Decision:  Decrease Atenolol to 50 mg/day, increase Lisinopril to 40 mg/day, add Clonidine 0.1 mg bid, add Amlodipine 10 mg qd. 

Treatment Decision:  Stop clonidine, continue Atenolol 50 mg/day, Lisinopril continued at 40 mg/day, increase Amlodipine 10 mg bid.

Treatment Decision:  Keep patient on current medication regime, patient returned to normal hemodynamic state with BP levels at home under control.

Reimbursement

ICG is nationally-approved by Medicare for five patient indications including heart failure and dyspnea.  In most states, the local Medicare carrier also covers the use of ICG for drug resistant hypertension.  The allowable frequency by Medicare is one test per physician per patient service date as medically necessary.  The 2009 national average reimbursement level by Medicare for ICG is $34.14.   The CPT code for Medicare reimbursement is 93701.

Multiple third party payers such as Aetna, Tricare/Humana and some BlueCross BlueShield and Medicaid carriers also cover ICG. 

¹Lloyd-Jones, Adams R, Carnethon M, et al.  Heart Disease and Stroke Statistics—2009 Update.  A report from the American Heart Assoiation Statistics Committee and Stroke Statistiscs Subcommitte.  Circulation. 2008.

²Schappert SM, Nelson C. National Ambulatory Medical Care Survey: 1995–96 summary. Vital and health statistics. Series 13. No. 142. Washington, D.C.: Government Printing Office, November 1999. (DHHS publication no. (PHS) 2000-1713.)

³Taler SJ, Textor SC, Augustine JE. Resistant hypertension: Comparing hemodynamic management to specialist care. Hypertension. 2002 May:39(5):982-988.

⁴Smith RD, Levy P, Ferrario CM. Value of noninvasive hemodynamics to achieve blood pressure control in hypertensive subjects. Hypertension. 2006 April:47(4):769-775.

⁵Sanford T, et al.  Amer J Hypertens 2005;18:87S-91S