Simulation of the QRS complex using papillary muscle positions as the site of early activation in human subjects.

BACKGROUND: Simulation of the electrical activation of the heart and its comparison with real in vivo activation is a promising method in testing potential determinants of excitation. Simulation of the electrical activity of the human heart is now emerging as a step forward for understanding and predicting electrophysiologic patterns in humans. Initial points of excitation and the manner in which the activation spreads from these points are important variables determining QRS complex characteristics. It has been suggested that in humans, the initial excitation of the left ventricle is a primary determinant of QRS complex characteristics, and that excitation begins at the papillary muscles and septum, where the fascicles of the left bundle branch insert. The aim of this study is to test the hypothesis that QRS duration and direction of QRS axis in the frontal plane have excellent agreement between real QRS and simulated QRS using papillary muscle position to indicate the border of the origin of early ventricular activation. METHODS: Fourteen healthy adult volunteers were included in the study. Magnetic resonance imaging data were obtained to assess the papillary muscle positions. Twelve-lead electrocardiographic (ECG) recordings were used to obtain real ECG data for assessment of QRS duration and QRS axis in each subject. Simulation software developed by ECG-TECH Corp (Huntington, NY) was used to simulate the ECG of each subject to determine simulated QRS duration and QRS frontal plane axis. QRS duration and QRS axis data were compared between simulated and real ECG and agreement between these variables was calculated. RESULTS: Seventy-nine percent of subjects had a difference of the QRS duration between real and simulated ECG of less than 10 milliseconds. The calculated strength of agreement between simulated and real QRS duration was 71% and considered as "good" (kappa statistics). In 70% of subjects, the difference in the QRS axis was less than 10 degrees . The calculated strength of agreement between simulated and real QRS axis was 80% and considered as "excellent" (kappa statistics). CONCLUSIONS: The results of this study suggest that the sites of the initiation of electrical activity in the left ventricle, as assessed by the positions of papillary muscles, may be considered as primary determinants of the QRS duration and QRS axis in humans. This knowledge may help in predicting normal QRS characteristic on a patient-specific basis. In this study, simulation of the QRS complex was based on papillary muscles from human hearts.

The relationship between mitral papillary muscles positions and characteristics of the QRS complex.

BACKGROUND: QRS complex characteristics are considered to be one of the most significant diagnostic and prognostic determinants for assessment of several cardiac conditions. However, there is a large variability of the QRS complex even among "normal" individuals. This study was based on 2 assumptions: (1) that the portion of the left ventricular endocardium activated earliest is directly supplied by the "fanlike" distribution of the anterior, middle, and posterior fascicles of the left bundle branch, and (2) that the anterior and posterior fascicles course toward their respective mitral papillary muscles. These structures could therefore serve as anatomical landmarks to indicate the borders of this fanlike distribution of primary "start points" of left ventricular activation. AIMS: The primary aim of this study is to test the hypothesis that location of both papillary muscles closer to the septum correlates with longer QRS duration. The secondary aim of the study is to test the hypothesis that the balance of the distances of the anterior and posterior papillary muscles from the septum is related to the direction of the frontal plane QRS axis. METHODS: The study population consisted of 16 healthy adult volunteers with a mean age of 26 +/- 9 years, mean height of 170 +/- 12 cm, and mean weight of 68 +/- 10 kg. Measurements were done on the magnetic resonance images from all study subjects. Positions of papillary muscles were assessed as a predictive variable of QRS duration. RESULTS: A significant correlation was found between the closer position of both papillary muscles to the septum and longer QRS duration (R = 0.7, P = .02). Subjects with higher ratio of anterior papillary muscle vs posterior papillary muscle free wall angle correlates with inferior rotation of the average axis of QRS complex in the frontal plane (R = 0.5, P = .04). CONCLUSIONS: The positions of the papillary muscles in relation to the free wall and septum wall can be predictive of both QRS duration and the direction of the QRS complex of the heart. These results might provide a new basis for prediction of QRS complex characteristics of an individual and, thus, differentiate between real QRS complex abnormalities and variants of normal.

Determination of the mitral papillary muscle positions by the septal-to-free wall arc ratio method.

BACKGROUND: Determination of mitral papillary muscle positions is of increasing interest in wide spectrum of clinical cardiology fields. Particularly, relative positioning of the papillary muscles between the inter-ventricular septum and the left ventricular free wall is of interest. A reproducible method for determination of papillary muscle positions has not been established. In this study a new 'septal-to-free wall arc ratio' (SFAR) method for measuring papillary muscle positions is presented. The reproducibility of the SFAR method between echocardiographic (ECHO) and magnetic resonance (MRI) modalities and between observers is tested. METHODS: Twenty subjects with structurally normal hearts in whom both MRI and ECHO were performed in 2007 were included in the study. Papillary muscle positions were determined using the SFAR method. Inter-modality (ECHO and MRI) and inter-observer reproducibility of the methods was assessed by calculating correlation coefficients and the mean difference from agreement. RESULTS: The inter-modality correlation of the SFAR method was 0.80 (P < 0.0001) for both papillary muscles. The mean difference of measurements from agreement was 4% for the superior and 2% for the inferior papillary muscle. The inter-observer correlation was 0.93 (P < 0.0001) for superior and 0.90 (P = 0.0002) for inferior papillary muscle. The mean inter-observer difference from agreement was 2% for superior and 3% for inferior papillary muscle. CONCLUSIONS: The SFAR method may be applied in wide range of both scientific and clinical medical fields as a reproducible method for determination of papillary muscle positions with the benefit of estimation of relative papillary muscle positions both from the septum and the free wall.