Who
could say no to a treatment that yields better results,
with fewer complications, at lower cost? That's precisely
the claim being made for a new clot-busting device that
has outperformed the gold standard, according to data
presented at the International Symposium on Endovascular
Therapy (ISET) conference held in Miami Beach on January
16-20.
Typically, acute clots in the extremities
are dealt with by infusing clot-dissolving drugs. The
process takes many hours, all the while leaving the
patient exposed to a high risk of bleeding. But this
new device can dramatically speed the process, enough
to spare many patients even a single night's hospital
stay.
"Using this device we may be able
to begin doing infusions [of the lytic drug] without
the patient having to stay overnight," says Dr Thomas
McNamara, chief of vascular and interventional radiology
at UCLA Medical Center in Westwood, CA, who presented
his group's findings at the meeting. "When you don't
have overnight infusion, you almost never have bleeding."
THE
SOUND OF SUCCESS
The device in question is an ultrasound catheter. Like
existing catheters used in clot lysis, it has channels
for drug delivery, but it boasts one added feature —
a central wire bearing up to five groups of six tiny
ultrasound transducers. The ultrasound loosens the tangle
of fibrins that make up a clot, allowing the drugs to
penetrate faster and interact with a broader surface
area. At the same time, the ultrasound propels the drug
into the clot as though it were under pressure. The
result is a faster and more thorough lysis.
Ultrasound is already used to break
up kidney stones and even to attack some tumours. But
the role of ultrasound in the dissolution of blood clots
isn't to break them up. In fact, avoiding "fragmentation
emboli," a more refined term for what's left over when
a clot is smashed to bits, is a vital prerequisite for
treating peripheral blood clots because those loose
fragments can make their way to the lungs, leading to
a potentially fatal case of pulmonary embolism if undetected.
Dr McNamara stresses that the ultrasound's purpose is
purely to facilitate drug delivery, not to break the
clot up. And unlike high-power applications such as
are seen in cancer therapy, this level of ultrasound
neither raises temperature nor damages tissue. Even
the loosening effect on the clot itself is transient.
Under the microscope, the fibrins
in a clot look like a loose ball of yarn. Photos shown
to the ISET conference by Dr Keith Sterling, a specialist
in vascular radiology at Inova Alexandria Hospital in
Virginia, showed a notable loosening of these fibres
after ultrasound.
PROOF
IN NUMBERS
Two trials of the device were presented at ISET. Dr
McNamara's study involved 66 patients with peripheral
arterial occlusive disease, which, as the name suggests,
can result from clot formation in a peripheral artery.
The clots were completely dissolved in 58 of these patients
and only one suffered non-fatal major bleeding. This
success rate of 88% compares to a rate of 66% achieved
in a comparable study of the current gold standard.
And the bleeding rate of 1.3% represents a large improvement
on the 12.5% rate seen with conventional treatment,
says Dr McNamara. "It's a big step forward."
That 92% reduction in bleeding
complications is largely due to reduced time of infusion,
says Dr McNamara. The 88% lysis rate was achieved after
17.5 hours, compared to 24.4 hours with the less effective,
conventional treatment.
The time savings were even more
dramatic among the 33 patients treated by Dr Sterling
for deep venous thrombosis (DVT), the formation of a
clot in a deep vein, usually in the leg or pelvis. The
new technique dissolved 70% of clots after 23.3 hours.
In comparison, two large studies of existing treatments
for DVT found that 31% of clots were completely dissolved
after 37 hours it took 53 hours to get that number up
to 38%. Once again, bleeding was significantly reduced
with the ultrasound-enhanced device, from 11.4% in the
gold standard studies to only 5% of patients in this
trial.
SAVING
TIME AND MONEY
Current data suggests that about one in 20 people in
industrialized countries can expect DVT at some point
in their life. Almost 60,000 Canadians are hospitalized
each year and associated mortality is high, about 21%
over one year among over-60s, mostly due to pulmonary
embolism. (For more on PE diagnosis, see "Closing
the net on deadly clots")
Each hospitalized case costs more
than $2,500, according to a 2003 survey of Canadian
DVT statistics published in the New England Journal
of Medicine. This adds up to a total annual cost
in the $100 million range.
The ultrasound catheter has no
price tag yet, but it's unlikely to be outrageous, since
it merely combines two existing technologies. But the
savings in bed time and reduced complications not to
mention the lower risk of pulmonary embolisms implied
by these findings could be significant if further study
bears out the technique's early promise.
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