Adverse cardiac events, including acute myocardial infarction and sudden cardiac death, may be triggered during and after major snowstorms by colder temperatures and the physical exertion expended with snow shoveling 1–8
. We present a case series of 6 patients who presented with an acute ST elevation myocardial infarction (STEMI) all within a 24-hour period during an unprecedented snowfall: 4 patients experienced symptoms while shoveling snow. Patients with a history of coronary artery disease and previous coronary stent placement, all presented with subacute stent thrombosis; a unique presentation which has not been previously described in other cases of “snow - shoveler’s infarction” 9–12
In one 24-hour period, from Saturday, December 19, 2009 to Sunday, December 20, 2009, 6 patients were taken emergently to the cardiac catheterization laboratory at the University of Virginia, Charlottesville, Virginia with the diagnosis of STEMI; 4 underwent primary percutaneous coronary intervention (PCI), and 2 underwent rescue PCI following failed thrombolysis. Medical history, medications on admission, laboratory values, 12-lead electrocardiographic results, treatment delay, angiographic findings, procedural details, and in-hospital outcomes for all patients were recorded.
We searched the literature for reported cases of “snow -shoveler’s infarction ”. We review ed the MEDLINE database (Nation al Library of Medicine, Bethesda, MD) from 1970 to 2010. The following key words were used in the search: ST elevation myocardial infarction, acute coronary syndrome, infarction, snow, snow shoveling, snow blowing, snow removal. We reviewed only articles written in English. We also gathered meteorological data from the McCormick Observatory located on the campus of the University of Virginia, for the time period of December 18, 2009 to December 20, 2009 (data from previous months was reviewed for comparison). Lastly, we searched our cardiac catheterization laboratory database to determine: (1) the daily number of patients with STEMI referred for primary PCI, and (2) the daily number of STEMIs that were a result of subacute stent thrombosis from December 2008 to December 2009.
The baseline characteristics of the patients are listed in . Of the 6 patients, 4 had a history of previous stent placement (2 with drug-eluting stents, and 2 with bare metal stents) (); all 4 patients presented with subacute stent thrombosis, and all but one were on chronic dual anti-platelet therapy. Symptom onset to arrival in the emergency department ranged from 40 minutes 6 to 264 minutes. The infarct-related artery was the left anterior descending artery in 3 patients and the right coronary artery in 3 patients; all patients underwent intervention of the infarct related artery, and one patient required an intra-aortic balloon pump. New congestive heart failure was diagnosed in 3 patients, and 1 patient died of cardiogenic shock.
Characteristics of 6 patients presenting with ST segment elevation myocardial infarction during a snow storm
Data obtained from the University of Virginia cardiac catheterization laboratory database revealed a doubling of STEMI cases within a single 24-hour period compared to any other 24-hour period over the past year (). Moreover, there was a sharp increase in the incidence of subacute stent thrombosis on December 20, 2009 (diagnosed in 4 of the 6 patients), compared t o daily rates seen over the past year. The spike in the STEMI rate correlated with greater snowfall (), as well as colder temperatures, lower atmospheric pressure, and higher wind gusts (). A total of 20.5 inches of snow was recorded, the largest single-storm snowfall total for the month of December in the Charlottesville, Virginia area since December 1969 when 16 inches was recorded.
Figure 1 Daily number of patients with ST elevation myocardial infarction undergoing primary percutaneous coronary intervention at the University of Virginia from December 1, 2008 to December 31, 2009 (top panel), and daily number of patients with subacute stent (more ...)
Figure 2 Hourly meteorological data as recorded by the McCormick Observatory on the campus of the University of Virginia, Charlottesville, Virginia. Temperature (top panel) in degrees Fahrenheit (°F) from 12 am December 18, 2009 to 3:57 pm, December 20, (more ...)
Our review of published reports resulted in a total of 4 case series that fulfilled our search restrictions 9–12
. These articles were reviewed by 2 of the authors (RJ and ECK). Pertinent information including year and location of the snowstorm, maximum snowfall recorded (inches), number of patients, cardiac history and whether symptoms were preceded by snow shoveling were collected for these studies and summary data, including our series, is shown in .
Summary of case series of patients presenting with myocardial infarction during or after a heavy snowfall
The phenomenon of increased rates of adverse cardiac events occurring during the cold winter months was originally described more than 60 years ago 13
; patients with pre-existing coronary artery disease are especially vulnerable 14
. Temperature changes and seasonal variations have been associated with an increase in the incidence of myocardial infarction and sudden cardiac death 2,6,7,15
, and have also been associated with infarct size 16
. Numerous studies have suggested that strenuous exertion (such as snow shoveling) in the days following heavy snowfalls is associated with increased cardiac events 1,2,8,10,17–21
. In fact, strenuous exercise of other types has been associated with plaque rupture and subsequent thrombosis 22,23
Snow shoveling results in significant increases in heart rate, systolic blood pressure, and rate–pressure product 5
, and is often undertaken in the early morning hours when circadian changes may play a role 24
. Moreover, strenuous exercise and colder temperatures have been associated with changes in blood rheology including increased platelet activation, increased fibrinogen, and increased blood viscosity 25,26
, and a hazardous effect on blood pressure 27
. It is possible that a combination of these factors may trigger an acute cardiac event, particularly in those with underlying coronary artery disease who are habitually sedentary 28–30
. Thus, patients with known coronary artery disease (particularly those with a history of coronary stenting) and sedentary persons with cardiac 8 risk factors, should be cautioned regarding the increased myocardial demands of snow shoveling.
Our study has limitations. First, because of the inherent nature of a case series, ours was descriptive and limited by lack of a control group. Second, complete demographic data was not available for many of the patients previously reported in the literature. Third, we do not have blood test results for levels of fibrinogen, platelet activation, or blood viscosity since these are not routinely measured as part of standard of care.