emphysema of any etiology is nearly always caused by chronic obstructive pulmonary disease , and has been shown to be strongly and quasidiagnostically associated with a vertical frontal p wave axis.111 in previous investigations , we have determined that a vertical p wave axis ( > 60 degrees ) during sinus rhythm can be used as a lone criterion to screen for pulmonary hyperinflation / emphysema , with sensitivity and specificity both being above 90%.4,5,8 previous studies have also suggested that the degree of p vector verticalization has an inverse correlation with qualitative lung function8,9 and quantification of radiographic emphysema.12,13 a vertical p vector on a surface 12-lead electrocardiogram can be determined by two methods using limb leads , ie , a p wave amplitude in lead iii greater than in lead i or a negative p wave in avl,1,5,8 although both these electrocardiographic findings suggest a vertical p vector and theoretically both should be simultaneously present in all the patients with a vertical p vector . however , preliminary observations from our previous investigations had suggested that this is not the case in the clinical setting . thus , the purpose of our current investigation was to determine which set of limb leads would be better for identifying the vertical p vector of emphysema in adults , given that this has not been investigated previously . a p wave amplitude in lead iii greater than in lead i indicates a p axis > 60 degrees , a p wave amplitude in lead iii equal to that in lead i indicates a p axis of 60 degrees , and a p wave amplitude in lead iii smaller than in lead i indicates a p axis < 60 degrees . a negative p wave in avl indicates a p axis > 60 degrees , while a flat or equiphasic p wave in avl indicates a p axis of 60 degrees and a positive p wave in avl indicates a p axis < 60 degrees.1,2,5,8 our plan was to conduct this investigation in patients having a known diagnosis of emphysema with a working hypothesis , that the set more often showing p wave verticalization would be a more sensitive ( better ) marker for diagnosis of emphysema . thus , we aimed to investigate whether a p wave amplitude in lead iii greater than that in lead i is a better marker of emphysema than an inverted p wave in avl . we recorded 12-lead electrocardiograms at rest using a standard technique in unselected consecutive patients with a known diagnosis of emphysema and scheduled for a routine follow - up visit in the pulmonary clinic at our institution between march and april 2012 , with the aim of obtaining a total of 100 patient electrocardiograms after application of the exclusion criteria . inclusion criteria were age > 45 years,59 normal sinus rhythm , a prior confirmed diagnosis of emphysema with a documented clinical history , chest radiographs , and pulmonary function tests . we excluded patients aged younger than 45 years , those not in normal sinus rhythm , and those with poor quality tracings . patients younger than 45 years of age were excluded because a vertical p wave axis may be a normal finding in healthy children and young adults.1,5,8 paced rhythms were also excluded . the electrocardiograms were then analyzed individually by all the authors using a handheld loop magnifier to determine the frontal p wave axis / frontal p vector by accounting for the p wave amplitudes in leads i , iii , and avl . all patients enrolled in the investigation had a documented diagnosis of pulmonary emphysema supported by clinical history , chest radiographs ( findings of increased radiolucency of the lungs , a flat diaphragm , and a long , narrow heart shadow ) , and pulmonary function tests . pulmonary function tests showed an obstructive airway pattern ( forced expiratory volume in one second / forced vital capacity ratio [ fev1/fvc ] < 0.70 and a forced expiratory volume in one second [ fev1 ] < 80% of predicted ) without significant bronchodilator reversibility . electrocardiographic data for the 100 patients were divided into three categories depending on the frontal p wave axis , ie , > 60 degrees , 60 degrees , or < 60 degrees , by each criterion ( ie , accounting for the p amplitude in leads iii and i and the p wave in avl ) . a correlation between the frontal p axis and fev1 the mean ( standard deviation ) age of the patients was 68.2  9.9 years , of whom 41% were male . ninety - four percent of the patients had an active or remote smoking history , with an average of 48.3  28.5 pack - years of smoking . the mean p vector was 68.6  11.4 degrees and did bear an inverse correlation with fev1 ( r = 0.52 ; p < 0.001 ) . of 73 study patients who had also undergone a conventional computed tomographic scan of the chest , 66 ( 90.4% ) had evidence of emphysematous changes . table 2 shows the p wave axis based on p wave amplitude in leads i and iii . eighty - eight of the 100 patients had a p wave in lead iii greater than the p wave in lead i , eight had a p wave in lead i equal to that in lead iii , and four had a p wave greater in lead i than in lead iii . sixty - six of the 100 patients had a predominantly negative p wave , 22 had a flat p wave , and 12 had a positive p wave in avl . an electrocardiographic tracing showing p wave amplitude in lead iii greater than in lead i and an unequivocally negative p wave in avl during sinus rhythm is shown in figure 1 . the study results demonstrated that a p wave amplitude in lead iii greater than in lead i ( sensitivity 88% ) is a more sensitive marker of emphysema than an inverted p wave in avl ( sensitivity 66% ) . frontal p wave verticalization has been shown to have a close correlation with emphysema and has been extensively studied in previous investigations.18 moreover , increasing verticality of the frontal p vector correlates with increasing degrees of airway obstruction,8,9 degree of depression of the diaphragm,3 and radiographic quantification of the disease.12,13 a possible mechanism of p wave axis verticalization in lung hyperinflation is that the right atrium is firmly attached to the diaphragm by a dense pericardial ligament around the inferior vena cava.3 with progressive flattening of the diaphragm , the right atrium is distorted / displaced inferiorly , causing a significant rightward deviation ( verticalization ) of the p wave axis . a prospective blinded investigation of patients with purely ( fibrotic ) restrictive , compared with purely obstructive pulmonary disease showed the p axis to follow the level of the diaphragm , such that patients with restrictive lung disease and high diaphragms had horizontal and leftward p axes , while patients with low diaphragms and obstructive lung disease had vertical p axes.3 in the study by baljepally et al,5 the sensitivity and specificity of a p axis > 60 degrees for emphysema was found to be 89% and 96% , respectively . in another study by chhabra et al,8 sensitivity and specificity of a vertical p axis for diagnosing emphysema was 94.7% and 86.4% , respectively . from prior correlation studies,5,8 it is clear that a vertical p axis on an electrocardiogram is the single most common screening tool , which is highly sensitive and specific in diagnosing emphysema at a glance.5,8 both studies5,8 used electrocardiographic criteria ( a p amplitude in lead iii greater than in lead i and/or a dominantly negative p wave in avl ) to determine p wave verticalization . in the present study , we took this further by investigating the percentage of patients with emphysema who have a dominantly negative or inverted p wave in avl compared with a p wave in lead iii greater than that in lead i ; 88% of the emphysema patients had a p wave in lead iii greater than that in lead i , and only 66% of the patients had an inverted or negative p wave in avl . in an ideal theoretical setting , the p wave amplitude should be negative in avl when the p wave amplitude in lead iii is greater than in lead i ( suggesting a vertical p vector ) , but this was not found in a practical clinical setting , which could be possibly due to a commonly encountered variable / high skin resistance or poor surface contact at avl producing a spurious  augmented  extremity ( unipolar ) lead abnormality.14 thus , the results suggest that the bipolar lead set is more sensitive for rapid characterization of emphysema than the unipolar set . all patients enrolled had a known diagnosis of emphysema ( based on chest radiographs and pulmonary function tests ) , so the specificity of both these electrocardiographic criteria for diagnosing emphysema could not be estimated in the current study . emphysema was diagnosed based on clinical history , chest radiographs , and pulmonary function tests . high resolution computed tomographic scanning was not used to confirm the diagnosis , and is known to have a higher sensitivity and specificity for diagnosing structural emphysematous changes . all patients enrolled had a known diagnosis of emphysema ( based on chest radiographs and pulmonary function tests ) , so the specificity of both these electrocardiographic criteria for diagnosing emphysema could not be estimated in the current study . emphysema was diagnosed based on clinical history , chest radiographs , and pulmonary function tests . high resolution computed tomographic scanning was not used to confirm the diagnosis , and is known to have a higher sensitivity and specificity for diagnosing structural emphysematous changes . the vertical p axis ( > 60 degrees ) on an electrocardiogram is a unique characteristic of obstructive pulmonary disease in adults and is the single most important tool for identifying emphysema by electrocardiogram , and serves as a virtual screening test at a glance . a p wave in lead iii larger than in lead i is a more sensitive marker for rapid identification of emphysema compared with an inverted p wave in avl .
backgroundpulmonary emphysema of any etiology has been shown to be strongly and quasidiagnostically associated with a vertical frontal p wave axis . a vertical p wave axis ( > 60 degrees ) during sinus rhythm 
 can be easily determined by a p wave in lead iii greater than the p wave in lead i ( bipolar lead set ) or a dominantly negative p wave in avl ( unipolar lead set ) . the purpose of this investigation was to determine which set of limb leads may be better for identifying the vertical p vector of emphysema in adults.methodsunselected consecutive electrocardiograms from 100 patients with a diagnosis of emphysema were analyzed to determine the p wave axis . 
 patients aged younger than 45 years , those not in sinus rhythm , and those with poor quality tracings were excluded . 
 the electrocardiographic data were divided into three categories depending on the frontal p wave axis , ie , > 60 degrees , 60 degrees , or < 60 degrees , by each criterion ( p amplitude lead iii > lead i and a negative p wave in avl).resultssixty - six percent of patients had a p wave axis > 60 degrees based on avl , and 88% of patients had a p wave axis > 60 degrees based on the p wave in lead iii being greater than in lead i.conclusiona p wave in lead iii greater than that in lead i is a more sensitive marker than a negative p wave in avl for diagnosing emphysema and is recommended for rapid routine screening .