Waitemata District Health Board has scored lowest in a national check on the proportion of patients suffering a suspected heart attack or serious angina to receive an important test within three days, researchers have found.

The Cardiac Clinical Network, supported by the Health Ministry, established in 2013 a target that 70 per cent of hospitalised patients with a suspected heart attack or serious angina receive invasive coronary angiography -- an imaging test that uses a catheter inserted through a blood vessel, dye and x-rays -- within three days of hospital admission.

Waitemata achieved 57.4 per cent, according to a paper in today's New Zealand Medical Journal based on data on all patients admitted to public hospitals with suspected "acute coronary syndrome" in the 12 months to November 2014.

Waitemata was the only DHB below 70 per cent among the nine health boards that have a hospital with on-site facilities for placing stents to help reopen blocked heart arteries.

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The other DHBs below 70 per cent -- Taranaki, Lakes, Tairawhiti, Hawkes Bay, West Coast and South Canterbury -- are among the 11 that do not have a stenting unit, also called an interventional catheterisation lab.

Waitemata's chief medical officer, Dr Andrew Brant, said his DHB was now exceeding the target.

The key developments had been the employment of an additional interventional cardiologist and changes at Waitakere Hospital which meant that when patients arrived there with a suspected heart attack, they were now transferred more quickly than before to North Shore Hospital's interventional catheterisation lab.

The authors of the journal paper say that in certain kinds of heart attack, higher rates of invasive coronary angiography and heart-artery grafting or stenting are linked to reduced rates of death, repeat heart attacks and readmission to hospital for unstable angina.

Delays in invasive coronary angiography are associated with increased recurrence of restricted blood flow to the heart arteries and an increase in hospital stays.

The researchers, mostly cardiologists, say that although there have been improvements in the timeliness of receiving angiography since before the introduction of the target in 2013, more work is needed.

Because they found the poorer performers were mostly DHBs without their own heart stenting unit, they propose new rules requiring such hospitals to send patients with suspected heart attacks or unstable angina to one that has a unit.

"This would facilitate early triage of patients, with immediate transfer of high-risk [heart attack] patients who will obtain the greatest benefits from early angiography."