In this context, clinical factors refer to the severity and description of ACS symptoms and a relevant past medical history, including the presence of cardiovascular risk factors. While symptom severity is self-explanatory, a relevant past medical history and cardiovascular risk factors warrant definition. A relevant past medical history refers to a previous diagnosis of any cardiac
condition that predisposes the individual to a future ACS event. These include angina, MI, PCI and coronary artery bypass graft (CABG). Cardiovascular risks in this context refer to factors that predispose the individual to develop an ACS event. The most common modifiable risk factors are smoking, diabetes hypercholesterolaemia and hypertension. These aforementioned factors appear to impact on pre-hospital delay time, either positively or negatively, and consensus has not been achieved with respect to the extent and duration of the delay-impact of the various factors.
Symptom descriptors and onset
Acute coronary syndrome symptoms that are continuous are associated with shorter pre-hospital delay times (Dracup & Moser 1997, Zerwic et al. 2003, Johansson et al. 2004a, Gartner et al. 2008, Rucker et al. 2008, Hwang et al. 2009, Khraim et al. 2009, DeVon et al. 2010, McKee et al. 2013). Furthermore, it has been suggested that the nature of symptom onset also exerts much influence over pre-hospital delay time in ACS (O’ Donnell & Moser 2012, O’ Donnell et al. 2013). Patients whose ACS symptoms are of slow onset are subject to protracted pre-hospital delay time, while those who experience fast onset symptoms have shorter pre-hospital delay times (O’Donnell et al. 2013). A combination of symptoms that are typical, severe and sudden in onset have been associated with shorter pre-hospital delay times (Ottesen et al. 2004, Foraker et al. 2008, Herlitz et al. 2010a, McKee et al. 2013).
Symptom descriptors associated with shorter pre-hospital delay times have varied across the spectrum of ACS categories; for example, continuous
symptoms were associated with shorter pre-hospital delay times for those diagnosed with MI, but not for those with unstable angina (McKee et al. 2013). The presence of atypical ACS symptoms and intermittent pain have been associated with increased pre-hospital delay time (Dracup & Moser 1997, Goldberg et al. 2002, McKinley et al. 2004, Hwang et al. 2006, DeVon et al. 2010). Overall, there is limited consensus in the literature with respect to the relationship between symptoms and pre-hospital delay time. The varied reports render it difficult to determine whether it is the actual symptoms, the nature of symptom onset, or a combination of these that contribute to increased pre- hospital delay time. It is therefore important that the complete range of ACS symptoms and their variability be disseminated to individuals to alert them to the potential seriousness of all symptoms. If this is achieved, then any ACS symptom and its onset could initiate the drive to seek treatment, as opposed to only those symptoms that are of rapid onset and cause the greatest discomfort.
Relevant past medical history
Researchers have reported inconsistent results with respect to pre-hospital delay times and relevant past medical history. Extensive research has been conducted to ascertain the association between pre-hospital delay time and a past history of acute MI (Johansson et al. 2004a, Gartner et al. 2008, Saczynski et al. 2008, Khraim & Carey 2009, Perkins-Porras et al. 2009) and cardiac procedures (Sheifer et al. 2000, Gartner et al. 2008, Goldberg et al. 2009). While researchers reported a reduction in pre-hospital delay time among those with a past history of MI, this finding is not supported consistently in the literature (Dracup & Moser 1997, Johansson et al. 2004a, Quinn 2005, Banks &
Dracup 2006, McKee et al. 2013). However, several researchers reported shorter pre-hospital delay times among those with a history of PCI and stent insertion (Ottesen et al. 2004, Perkins-Porras et al. 2008, Ting et al. 2010, McKee et al. 2013).
The finding that a history of PCI and stent insertion is associated with shorter pre-hospital delay times warrants consideration. This finding may relate to a common misperception that PCI procedures are curative. Individuals that present sooner to the ED with ACS symptoms may do so on the premise that something has ‘gone wrong’ with the inserted device, as opposed to thinking that the symptoms could be ACS related. For those not previously treated with PCI, the possibility of an ACS recurrence may have prompted the use of denial mechanisms, which can prolong pre-hospital delay times. While the reasons for early presentation to the ED have not been systematically explored, the importance of disseminating realistic information about the risk of a future ACS event is worth considering. This should include those who undergo PCI, as their self-perception of future risk may differ from others. For the cohort of other individuals who seek treatment more speedily, it has been suggested that this may be related to the fact that family members and treating physicians are more sensitised by memories of previous events (Gartner et al. 2008). However, it is also possible that following PCI procedures, individuals receive additional information about managing ACS symptoms, although this is not supported in the literature.
Cardiovascular risk factors
Cardiovascular risk factors predispose the individual to the development of ACS. While individuals cannot control their unmodifiable risk factors, those that are modifiable can be controlled, albeit to varying extents. The most common modifiable risk factors are smoking, diabetes, hypercholesterolaemia and hypertension. In general, the presence of modifiable risk factors is associated with increased pre-hospital delay time. Studies have shown a relationship between prolonged pre-hospital delay and hypertension (Sheifer et al. 2000, Moser et al. 2006, Goldberg et al. 2009, Khraim et al. 2009). Researchers have also reported an association between longer pre-hospital delay time and smoking (Goldberg et al. 2009, Khraim et al. 2009, Ting et al. 2010). However, with respect to smoking, a shorter pre-hospital delay time with respect to this variable has also been reported (Xanthos et al. 2010).
Some researchers did not report an association between hypercholesterolaemia and pre-hospital delay time (Khraim et al. 2009, McKee et al. 2013), which may be explained by the lack of an association between it and either prolonged or shortened pre-hospital delay time (Herlitz et al. 2010a, Park et al. 2012). There is consensus in the literature on the link between the condition of diabetes and increased pre-hospital delay times (Sheifer et al. 2000, Moser et al. 2006, Gartner et al. 2008, Goldberg et al. 2009, Khraim et al. 2009, Ting et al. 2010, Ängerud et al. 2013). This may be explained by the presence of autonomic neuropathy, which can result in silent ischaemia or the presence of atypical ACS symptoms among diabetic patients (McGinn 2005, Ryden et al. 2007, Tubaro et al. 2011). While the finding that diabetes is associated with increased
pre-hospital delay time, the suggestion that diabetics present with less typical ACS symptoms than their non-diabetic counterparts is not consistently supported in the literature (Ängerud et al. 2012, Ängerud et al. 2013).