Treating ST-segment elevation myocardial infarction (STEMI) quickly with percutaneous coronary intervention (PCI) following symptom onset was shown to save more heart muscle than longer symptom-to-balloon time (SBT) cases, pooled data from 10 randomized trials show.
Door-to-balloon time (DBT), however – a measure describing the time between a patient entering the hospital and receiving PCI – was not correlated with the same worsening of heart tissue damage for longer wait times.
The findings “emphasize the importance of efforts to increase public awareness of STEMI symptoms and the imperative for early medical system activation if the prognosis of patients with acute MI is to be further improved,” said the researchers and the American Heart Association (AHA).
The study was published online Thursday in Circulation: Cardiovascular Interventions, led by first author Björn Redfors, MD, PhD, of New York’s Cardiovascular Research Foundation, the New York-Presbyterian Hospital/Columbia University Irving Medical Center, and Sahlgrenska University Hospital, Sweden.
SBT and DBT are both considered important metrics in patients undergoing PCI for STEMI, the researchers noted, with timely reperfusion reducing infarct size and improving clinical outcomes.
DBT times for STEMI patients have been “effectively reduced” over the past decades with healthcare systems making it an important metric for hospital performance, they added. Current class I level of recommendation for DBT is 60 minutes or less in the EU and 90 minutes or less in the U.S. This has been associated with improved survival after primary PCI.
However, the researchers cited studies suggesting further reductions in DBT have not translated into substantial mortality improvements, adding that DBT may, therefore, not be the most important performance metric for the primary PCI chain of survival because – unlike SBT – it does not incorporate the total ischemic time, ignoring issues such as transfer delays.
Redfors and colleagues therefore set out to evaluate both SBT and DBT in 3,115 STEMI patients undergoing PCI in 10 randomized trials: INFUSE-AMI, APEX, CRISP, AIDA, LIPSIA-N-ACC, LIPSIA-STEMI, LIPSIA-ABCIX, EMERALD, AMIHOT-II and IMMEDIATE.
Clinical follow-up data were available for at least 6 months in each study, and patients’ infarct size in terms of percentage of left ventricular mass was assessed within 1 month after randomization by either technetium-99m sestamibi single-photon emission computerized tomography (SPECT) in three of the studies, or cardiac magnetic resonance imaging (CMR) in seven studies.
Secondary endpoints included microvascular obstruction (MVO), again as a percentage of left ventricular mass; and left ventricular ejection fraction (LVEF); as well as death, heart failure hospitalization (HFH) and reinfarction.
The patients were grouped into short (2 hours or less), intermediate (2 to 4 hours) or long (more than 4 hours) SBTs, and by short (45 minutes or less), intermediate (45 to 90 minutes) or long (more than 90 minutes) DBTs.
Median SBT was 185 minutes, while median DBT was 46 minutes. Median time to infarct size assessment after primary PCI was 5 days.
The researchers found a stepwise increase in infarct size according to SBT category, with an adjusted difference for intermediate versus short SBT by 2% (95% confidence interval [CI]: 0.4 to 3.5) and by 4.4% for long versus short SBT (95% CI: 2.7 to 6.1).
The same was not observed between the DBT categories.
MVO was also greater in patients with long versus short SBT (adjusted difference 0.9%; 95% CI: 0.3 to 1.4), but not between patients with intermediate versus short SBT (adjusted difference 0.1; 95% CI: -0.4 to 0.6). Again, there was no difference in MVO according to DBT. Results were similar in multivariable analysis with SBT and DBT included as continuous variables, the researchers noted.
LVEF data at time of infarct size assessment were available for all of the studies except for AMIHOT-II, including 2,538 patients. Similarly to MVO, LVEF was significantly lower in those with long SBTs but was not different between short and intermediate SBT groups.
Long DBT was also associated with significantly lower LVEF, but whereas increased SBT was an independent predictor of lower LVEF, DBT was not.
SBT also had a stronger correlation with the composite of death or HFH (adjusted risk of death or HF for SBT >4 hours versus ≤2 hours: 1.21; 95% CI: 0.79 to 1.87; p = 0.38) than DBT, “as would be expected” because infarct size and MVO after reperfusion therapy have both been proven to be independent predictors of subsequent HF and mortality, the researchers said.
Improve public awareness
The researchers said they believe the study to be the largest to date examining the relationships between SBT and DBT with infarct size and MVO in STEMI – the most common form of heart attack – but the results do mostly echo previous smaller studies.
The results highlight the importance of quick action from symptom onset, they stressed, and highlighted groups which fared the worst in terms of longer SBTs: older people, women, those with arterial hypertension, those with diabetes, and those with the left circumflex artery as the culprit vessel.
“Health care teams have worked to reduce door-to-balloon times and are achieving excellent results with a median time of 46 minutes. While we shouldn’t become complacent and relax our current standards of rapidly performing PCI as soon as possible after the patient reaches the hospital, this study suggests that major efforts to further shorten door-to-balloon times by 10 or 20 minutes might not translate to better PCI outcomes,” said corresponding author Gregg W. Stone, MD, of Mount Sinai Heart Health System, New York, in an accompanying AHA press statement.
“Our analysis indicates the more important and meaningful focus should be to shorten the delays from symptom onset to arrival at hospitals that can perform PCI. We must emphasize efforts to increase public awareness of heart attack symptoms and shorten the time it takes for patients to access emergency care.”
AHA President Mitchell S.V. Elkind, MD, MS, of Vagelos College of Physicians and Surgeons and New York-Presbyterian/Columbia University Irving Medical Center, stressed the particular importance of the findings given dipping patient attendance in emergency rooms during the COVID-19 pandemic, “indicating people aren’t calling 911, or they are delaying or avoiding critical care.”
It is unlikely that fewer heart attacks or strokes are occurring, he said, stressing that quick treatment “can be the difference between life and death.”
“As we have been urging even during the COVID-19 pandemic, don’t die of doubt. Call 911 as soon as possible.”
Redfors B, Mohebi R, Giustino G, et al. Time Delay, Infarct Size and Microvascular Obstruction After Primary PCI for ST-Segment Elevation Myocardial Infarction. Circ Cardiovasc Interv 2021 Jan 14. doi: 10.1161/CIRCINTERVENTIONS.120.009879.
Image Credit: Courtesy American Heart Association