Tackling resistant hypertension

SINGAPORE - Madam M, 72, came for a routine follow-up three years after I unblocked her heart arteries.

Her heart function had returned to normal after the coronary angioplasty, in which a flexible tube is threaded along the arteries to the clogged area and a balloon on the tube is inflated to clear the blockage.

But she complained of breathlessness and her systolic (maximum) blood pressure was in excess of 210 millimetres of mercury (mmHg). Hypertensive patients should get their blood pressure below 140/90mmHg.

Sometimes, Madam M's systolic blood pressure was so high that it sent her home monitoring system haywire, displaying an error message instead of a reading.

In spite of increased doses of her six different types of blood pressure medication, her blood pressure control remained poor.

Her daughter, a trained nurse, thought, perhaps, she was not taking her pills correctly. Determined to enforce compliance, the daughter packed the pills in little plastic bags and labelled them.

But faultless pill popping did not improve Madam M's condition.

Further scans and tests did not reveal any secondary causes exacerbating her blood pressure.

She had resistant hypertension, which is high blood pressure that does not respond to treatment.

About one in four adults here has high blood pressure, based on the National Health Survey 2010.

The majority have their high blood pressure controlled by taking two to three types of drugs.

The prevalence of resistant hypertension is between 3 and 5 per cent, not an uncommon problem given the many patients here.

Elderly at Risk

Patients with resistant hypertension tend to be elderly.

The common causes include non-compliance to medication, morbid obesity or other conditions such as renal artery narrowing and renal failure.

It is important to ensure that what appears to be resistant hypertension is not actually pseudo-hypertension or white coat hypertension where the blood pressure reading is elevated because of a patient's anxiety, but the actual blood pressure is not.

Persistent uncontrolled hypertension is a significant risk factor for stroke and heart disease.

Research has shown that each incremental increase of 20mmHg in systolic blood pressure and 10mmHg in diastolic (minimum) blood pressure above normal levels directly correlates to a doubling of the risk of death from cardiovascular disease over a 10-year period.

A 5mmHg reduction in blood pressure results in a 14 per cent drop in the risk of stroke, a 9 per cent drop in the risk of heart disease and a 7 per cent drop in the risk of death.

Treating the Kidneys

High blood pressure can be treated by targeting the kidneys.

The renal sympathetic nerves that surround the kidney arteries serve as a feedback channel for the brain and body to react to stress by sending a signal to tighten the kidney arteries.

This conserves water and salt for the body to cope with stressful events.

This feedback loop runs amok in people with resistant hypertension and heart failure, and sends excessive signals to the kidneys to react even in restful states.

By decreasing these signals, the kidneys stop reacting excessively and the blood pressure drops.

For about four decades from 1921, surgeons removed renal sympathetic nerves through laborious open surgery, which proved very effective for controlling hypertension.

But the surgery was associated with high complication rates. It was abandoned when effective medical therapy became available in the 1960s.

Recently, a minimally invasive method was developed to remove the renal sympathetic nerves, making it much safer than open surgery.

During the procedure, the patient is lightly sedated. With real-time X-ray guidance, a small guiding catheter no more than 2mm in internal diameter is inserted into the renal artery via a small puncture at the groin.

The tip of the catheter emits heat of up to 60 deg C, generated by low power radio frequency energy, to selectively disable the sympathetic nerves in the renal artery walls.

Surgey Not for All

But not all patients are suitable.

We have to ensure that the patient's resistant hypertension is not due to poor compliance to medication, white coat hypertension, or conditions such as kidney failure.

Currently, the procedure is approved for those with normal kidney function. The kidney arteries need to be relatively disease-free and more than 4mm in diameter.

The main complications are damage to the kidney arteries or side effects from using contrast agents.

Studies in Europe and Australia have shown a favourable safety profile, with patients who have been followed up for two years without untoward effects.

In Singapore, the National Heart Centre Singapore did the first such procedure in September 2011. I offered Madam M this new procedure to treat her resistant hypertension.

Her response was particularly fast. Her blood pressure started to drop the same day after the procedure and her breathlessness improved.

At her follow-up visit, she had an acceptable blood pressure level of 140/90mmHg, despite being on lower doses of blood pressure drugs.

Dr Jack Tan is a senior consultant at the department of cardiology and director of the coronary care unit and cardiology residency programme at the National Heart Centre Singapore (NHCS). His further speciality interests are in interventional cardiology and cardiac intensive care. He did his fellowship in complex coronary and peripheral vascular interventions at the UC Davis Medical Center in California, the United States, in 2007.


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