Kamel H, Soliman E, Heckbert S, Kronmal R, Longstreth WT, Jr, Nazarian S, Peter Okin P. P-Wave Morphology and the Risk of Incident Ischemic Stroke in the Multi-Ethnic Study of Atherosclerosis. Stroke. 2014
The Atherosclerosis Risk in Communities (ARIC) study group, already an important contributor of some of our most fundamental knowledge in cerebrovascular epidemiology, has provided us with an interesting piece of evidence that suggests a previously overlooked feature of a 12-lead electrocardiogram (ECG) called P-wave Terminal Force in V1 (PTFV1) may inform incident stroke risk. This follows on their previous work, which suggested an association between PTFV1 and incident stroke but did not control for atrial fibrillation (AF) in the cohort; a focus of this particular investigation is the role of PTFV1 after controlling for AF.
To start, what is PTFV1?!
My understanding is that PTFV1 is the degree of deflection of the terminal (or latter) aspect of a biphasic P wave. I see it most typically defined as a deflection of >40 mm2. It is a marker of morphologic and/or electrophysiologic dysfunction of the atria, related to P-wave dispersion and duration (other markers with the same implications). A better description of the relationship between these ECG markers and the cardiologic implications can be read here.
In brief, the investigators built on their previous findings of an association between PTFV1, a marker of atrial abnormality, and incident ischemic stroke. A major (and fair) criticism of their previous work is that those findings were not controlled for the presence of AF. This study, in a large cohort of > 6700 patients, was specifically designed to address this interaction, at least to the degree possible, so as to screen for an independent association between PTFV1 and incident ischemic stroke beyond the risk AF confers.
The event rate was fairly low, with only 121 strokes (1.8%) in a median of 8.5 years. AF was noted in 541 (8%) participants. However, after “adjusting for baseline confounders,” PTFV1 positivity was more strongly associated with stroke (hazard ratio [HR] per 1-SD increase, 1.21; 95% confidence interval [CI], 1.02-1.44) than AF (HR per 1-SD, 1.11; 95% CI, 1.03-1.21).
Although there are certainly some limitations to this investigation, as outlined in their discussion, this finding has interesting implications. The frustration of making a diagnosis of “cryptogenic stroke” in a patient with multiple cortical infarcts of varying ages, a morphologically abnormal left atrium and a swing-and-a-miss on prolonged outpatient telemetry is real and frequent, and the idea that any atrial abnormality – manifesting in AF or otherwise – confers ischemic stroke risk and may require treatment for risk reduction is an attractive premise for future research.
For sure, as regards incident stroke risk and ECGs, we should mind our ‘p’s and ‘q’s.