Are we underestimating the full potential of early thrombolytic treatment in patients with acute myocardial infarction?

When analyses are invalidated by erroneous assumptions

In a recent publication in the “International Journal of Technology Assessment in Health Care” (7), Kildemoes and Kristiansen claim to address “Cost-effectiveness of interventions to reduce the thrombolytic delay for acute myocardial infarction.” Their study is based on a “Master of Public Health Assessment” thesis published by Kildemoes in the year 2001 (6). Three years ago, the author was informed that several of her assumptions were incorrect. In this letter, we will address six of the erroneous assumptions made by Kildemoes and Kristiansen.

Response to an optimistic viewpoint

We appreciate the interests in our work and observe that we agree that earlier thrombolysis for AMI can reduce the AMI case fatality. The question is how much and at what price. There are no data available to directly address this issue, and we developed a simulation model to quantify costs and health consequences of less thrombolytic delay by using public awareness campaigns, telemedicine, or a combination of the two. Inevitably, such a model needs to be based on several uncertain parameter values. We performed a range of sensitivity analyses so readers of the analysis could see the effect of replacing our base case values with others that the reader might consider more appropriate. Due to space restrictions, we had to omit a table with sensitivity analyses that would have addressed several of the concerns Terkelsen and coworkers have.

Response to commentaries by Kildemoes and Kristiansen

§1.1. Recent data documents that not a “majority” but only 40% of Danish patients arrive at the hospital within 30 minutes of ambulance call (7;8). §1.2. The Dutch study confirmed that, even in areas with 13 minutes transport time to the hospital, comparable to the Danish scenery, a prehospital thrombolytic strategy reduced treatment delay by nearly 1 hour (5). §1.3. We appreciate that the authors confirm our viewpoint, that is, quoting that “the mortality reduction more than doubles up,” “if hospital delay is totally eliminated (corresponding to a delay reduction of 1 hour).” In the future, patients should be diagnosed before hospital admission and either treated before hospital admission with thrombolysis or transferred directly to interventional center for primary PCI. In both settings, the delay at the local hospital, averaging 1 hour, would be eliminated (1;8). §2.0. Kildemoes and Kristiansen may have misunderstood our arguments regarding the Boersma formula. We recommend that they read our previous viewpoint (9). We have no reason to believe that distribution of patient delay in Denmark differs significantly from other countries. Moreover, we are surprised that the case fatality estimates implemented by Kildemoes and Kristiansen differs significantly from findings in a recent Danish Health Technology Assessment and findings in previous meta-analyses (2;4;6). §3.1. For 7 years, the present group of authors have worked with telemedicine in the prehospital evaluation of patients. Our close collaborators, the ambulance operators and the company delivering telemedicine equipment, have confirmed our cost data, whereas they disagree with the cost data implemented by Kildemoes and Kristiansen. §3.2. Equipment for twelve-lead ECG acquisition is necessary when implementing prehospital diagnosis, irrespective of whether the diagnoses are established by telemedicine, by paramedics, or by physicians. §5. A 1-hour reduction in treatment delay is achievable by a prehospital diagnostic strategy, both in the setting of prehospital thrombolysis and in the setting of prehospital referral to interventional centers for primary PCI (6;8). This reduction in treatment delay should have a major impact on AMI fatality (also in Denmark; 3;6).

Reduction of treatment delay in patients with ST-elevation myocardial infarction: impact of pre-hospital diagnosis and direct referral to primary percutanous coronary intervention

AIMS

The majority of patients with ST-elevation myocardial infarction (STEMI) are admitted to local hospitals without primary percutaneous coronary intervention (primary PCI) facilities. Acute transferral to an interventional centre is necessary to treat these patients with primary PCI. The present study assessed the reduction in treatment delay achieved by pre-hospital diagnosis and referral directly to an interventional centre.

METHODS AND RESULTS

Two local hospitals without primary PCI facilities were serving the study region. Pre-hospital diagnoses were established with the use of telemedicine, by ambulance physicians, or by general practitioners. Primary PCI was accepted as the preferred reperfusion therapy in patients with STEMI. From 31 October 2002 to 31 January 2004 all patients transported by ambulance and transferred for primary PCI were registered. Patients with STEMI were divided into three groups: (A) patients diagnosed at a local hospital (n = 55), (B) patients diagnosed pre-hospitally and admitted to a local hospital (n = 85), and (C) patients diagnosed pre-hospitally and referred directly to the interventional centre (n = 21). When comparing group A with group B and C, no difference was found in age, sex, infarct location, or distance from the scene of event to the interventional centre, whereas the median time from ambulance call to first balloon inflation was 41 min shorter in group B compared with group A (P<0.001) and 81 min shorter in group C compared with group A (P<0.001).

CONCLUSION

In a cohort of patients scheduled for admission to a local hospital and subsequent transferral to an interventional centre for primary PCI, those diagnosed pre-hospitally had shorter treatment delay compared with those diagnosed in hospital, both in the setting of initial admission to a local hospital, and to an even larger extent in the setting of referral directly to the interventional centre.