Left atrial rhythm

Left Atria1 Rhythm Analysis by Intra-atria1

Electrocardiogram

and the Vectorcardiogram* WILLIAM S. FRANKL, M.D., MS. (MED.) and LOUIS A. SOLOFF, M.D. Philadelphia,

Pennsylvania

R

EPORTS HAVE appeared suggesting that pacemaker activity may originate in the left atrium. Apparent examples of this have been termed left atria1 rhythm.‘-lo The patients with this rhythm have had dextrocardia and other congenital lesions, mitral insufficiency, mitral stenosis, or coronary artery disease. Left atria1 rhythm has been diagnosed on the basis of the following electrocardiographic characteristics : (1) inverted P waves in lead I; (2) “dome and dart” P waves in lead Vr; and (3) inverted P waves in lead Vs. This last characteristic has been reported as most Further studies have suggested diagnostic. that there are three varieties of left atria1 rhythm: (1) t h ose with all three characteristics; (2) those with an inverted P in leads I and Ve but no “dome and dart” P waves in V1; and (3) those with an upright P in lead I, “dome and dart” P waves in V1 but an inverted P wave in Vs.= However, in all cases inverted P waves are present in leads II, III and aVF, a pattern that previously had been regarded as suggesting “nodal” (or “A-V junctional”) rhythm. Differentiation between nodal and left atria1 rhythm is difficult. The P-R interval is not helpful since analysis of tracings suggesting left atria1 rhythm has revealed short, normal, or prolonged values. 5 It has been suggested that vector analysis of the P wave should be helpful in differentiating the two rhythms because of the difference in origin of the P wave. A-V nodal and junctional tissues lie just behind the medial leaflet of the tricuspid valve. Pacemaker or “automatic” cells are also thought to

lie in the interatrial septum, at the junction of the pulmonary veins with the atrium, and in These cells are the left atrioventricular ring.ll considered to be the source of left atria1 If these anatomic concepts are correct, rhythms. the result should be a mean P vector directed posteriorly, superiorly and to the left with nodal rhythms. The posterior direction is crucial since there is little atria1 tissue anterior to the A-V node. The mass of atria1 tissue lies posterior to the A-V node and to its left.6 This direction of depolarization has been suggested by older studies.12 The majority of cases with left atria1 rhythm, on the other hand, are thought to have a pacemaker located posteriorly in the left atrium because of the anterior direction of the P axes in Since both right and the right precordial leads. left atria1 vectors point in the same anterior direction, “dome and dart” P waves are inscribed in lead Vr. Thus, in most cases diagnosed as left atria1 rhythm, the direction of atria1 depolarization has been rightward, superior and anterior.6 The failure of all cases of left atria1 rhythm to show “dome and dart” P waves in V1 and inverted P waves in lead I was ascribed to an occasional lateral or anterior position of the pacemaker in the left atrium.2 To define more definitely the difference between left atria1 rhythm and nodal rhythm we decided to utilize intra-atria1 electrocardiograms and vectorcardiograms, which more accurately portray vectorial forces than scalar electrocardiograms. Intra-atria1 leads bring us closer The vectorcardiogram to the electrical events. approximates true vectorial forces more closely

* From the Divirdon of Cardiology, Department of Internal Medicine, Temple University Health Sciences Center, Philadelphia, Pa. This study was supported by U. S. Public Health Service Grant No. HE-05712-02. Address for reprints: William S. Frankl, M.D., Temple University Health Sciences Center, 3401 North Broad St., Philadelphia, Pa. 19140. VOLUME

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Frank1 and Soloff by utilizing and three

a more

portraying dimensional

nearly

spatial

accurate

events

lead

system

in a more

nearly

manner.

METHODS AND MATERIALS Scalar electrocardiograms were recorded with a direct writing Cambridge electrocardiographic apparatus or by the six channel Schwarzer PhonocardiographElectrocardiograph Recorder. Intra-atria1 electrocardiograms were inscribed by passage of a polyethylene tubing with 0.02 cm. outside diameter and 0.008 cm. wall thickness through an 18 gauge thin wall percutaneous needle which had been inserted into a medial antecubital vein in the right arm. By this method a catheter was quickly placed into the right atrium. A 5 per cent saline solution to which 10 mg. of heparin had been added was allowed to drip through the catheter, creating a conduction bridge. The patient and the Schwarzer recording apparatus were grounded. A 23 gauge needle was inserted into the end of the catheter, and an alligator clip joined to the precordial electrode in lead Vi. An intra-atria1 electrocardiogram was recorded in addition to simultaneous external leads Vz through VS. Hechtr3 demonstrated that intracavitary atria1 potentials displayed a QRS type of deflection often with an associated atria1 T wave. He named these potentials P,, Pas, PQRs, Pa, Ps, Pr, the last indicating the atrial In the high right atrial level, large Pas T wave. complexes are seen that often are larger than the actual QRS. This observation indicates that the exploring electrode is adjacent to the upper portion of As the exploring electrode is moved the sinus node. down through the atrium, a small Pa wave appears and becomes larger as the atrium is traversed toward the junctional area. In the low atria1 and junctional areas the P wave decreases in voltage with Pa and Ps waves present. When the ventricle is entered the P becomes upright and resembles that seen in external recordings. We have made such recordings and have found them identical to those just described. An example of such a tracing in a patient with normal sinus rhythm is shown in Figure 1. Vectorcardiograms were inscribed by utilizing the Frank lead system, a Hewlett-Packard Model 1520A Vector System, a Hewlett-Packard Model 780-6A Visoscope and a Model C04-197A Oscilloscope Camera, which produces Polaroid prints of the oscilOrthogonal electrocardiographic loscopic image. leads VX, VY and VZ were recorded, as well as frontal, left sagittal and horizontal plane loops with special reference to the P waves. Magnification of the P loop was sought to ascertain direction more clearly. The loops were interrupted at intervals of 1 msec., with the leading edge of the teardrops indicating the direction of the loop. The T loop was obliterated and not recorded in any of the tracings. Four patients whose scalar electrocardiograms were thought to be highly suggestive of left atrial rhythm were studied by these methods.

Figure 1. Intra-atria1 electrocardiogram. normal sinus rhythm.

Patient

with

CASE HISTORIES CASE 1. A 44 year old Caucasian woman was admitted to the otology service of Temple University Health Sciences Center on June 20, 1967. She had experienced drainage from the left ear since a mastoid operation at age 15. About one year prior to admission, the ear had become painful and the condition had finally led to this admission. She had experienced gestational hypertension but never had had other symptoms or signs of cardiovascular disease. Physical examination revealed that she weighed 89 lb. and was 5 ft., 1% in. tall; blood pressure was 150/90 mm. Hg. Examination was unremarkable except for pre- and postauricular sinuses of the left ear draining foul-smelling mucoid material, a culture of which reThere vealed group A beta-hemolytic streptococci. were no abnormal cardiovascular findings. Chest roentgenogram revealed a heart of normal size and position in the thorax. The initial electrocardiogram (Fig. 2A) revealed a regular rhythm at a rate of 88 beats/min. The P waves were inverted deeply in leads II, III, aVF and Va through Vs. The P wave had a low voltage “dome and dart” configuration in Vr and VZ. In lead I, the

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Case 1. Initial electrocardiograms. A, “left atrial” rhythm; normal sinus rhythm several days later

P waves were of very low voltage and slightly inverted. The remainder 0:’ the tracing was unremarkable. The tracing fits all of the previously mentioned criteria for left atria1 -rhythm. During induction of anesthesia for biopsy of the ear, a scalar electrocardiogram revealed repeated change in the rhythm from an obviously sinoatrial origin to a left atria1 (or nodal) origin. After surgery, sinus rhythm became established for a short time (Fig. 2B). An intra-atria1 ektrocardiogram performed on June 27 (Fig. 3, A to C) showed wandering of the pacemaker from an obvious Gnoatrial origin to a left atria1 (or nodal) origin. Vectorcardiograms were performed the same day, during left atrial rhythm (Fig. 4), and on June 30, during sinus rhythm (Fig. 5). Biopsy of the lesion revealed a squamous cell carcinoma, and a ragdical resection of left ear and temporal bone was performed on July 5. At no time during or after operation did cardiovascular signs arise. CASE 2. A 69 year old Caucasian woman was admitted to Temple University Health Sciences Center on July 12, 1967, with a history of increasing weakness, shortness of breath, difficulty in swallowing, nausea and vomiting. During the month prior to admission she had experienced profound anorexia and a weight loss of 20 lb. Previous admissions in 1964, VOLUME22, NOVEMBER1968

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1966 and March 1967 had been for diabetes mellitus, hypertension, ischemic heart disease and chronic renal insufficiency. She had been taking digoxin, chloropropamide, and chlorothiazide. She complained of two pillow orthopnea and classic angina pectoris relieved by nitroglycerin. Physical examination revealed an obese woman, 5 ft., 1 in. tall and weighing 170 lb., with blood pressure of 205/110 mm. Hg. There were crepitant rales at both lung bases. Heart size could not be determined because of obesity. Rhythm was regular, heart sounds distant, and no murmur was heard. Distinct atria1 and ventricular gallops were noted. There was bilateral pitting ankle edema. The rest of the examination was unremarkable. Chest roentgenogram revealed the presence of left ventricular enlargement and congestion of the pulmonary vessels. Laboratory studies revealed normal findings except for elevated blood urea nitrogen, creatinine and blood sugar levels. The initial electrocardiogram (Fig. 6A) taken on July 13 revealed sinus rhythm, with a heart rate of 96 beats/min., left atria1 abnormality and diffuse nonspecific ST-T changes at least partly due to digitalis. The second electrocardiogram (Fig. 6B) taken the following day revealed wandering of the atria1 pacemaker from an obviously sinoatrial origin to a left atrial focus with an inverted P wave in leads VI through Va and in a “rhythm strip” of lead II. Sub-

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A, B and 3. Case 1. Intra-atria1 electrocardiogram. C show representative strips recorded with precordial leads.

Figure

of palpitations. On physical examination the apical impulse was displaced slightly to the left. There was a precordial lift. A systolic ejection murmur and a late systolic click were heard along the left sternal border. The second sound was widely split and

sequent electrocardiograms revealed no evidence of left atrial rhythm. Vectorcardiograms were taken on July 14 during left atrial rhythm (Fig. 7). CASE 3. A 37 year old Caucasian woman was admitted to Temple University Health Sciences Center on April 25, 1967, for evaluation of an atria1 septal defeet diagnosed 14 years prior to admission. She was essentially asymptomatic except for recurrent episodes

moved only slightly with respiration. Chestroentgenogram revealed the cardiac silhouette to be at the outer limits of normal in size, with straightening of the left cardiac border and prominence of the p&monary artery segment. The pulmonary vasculature was quite prominent, consistent with a left to right shunt. The electrocardiogram (Fig. 8A) taken on April 25 revealed right axis deviation of the QRS in the frontal plane, low voltage in the limb leads and incomplete right bundle branch block. Cardiac catheterization revealed a slight elevation of right ventricular systolic pressure, and a moderately large left to right shunt at the atrial level, averaging Remaining laboratory studies revealed 2.2:l. normal findings. The patient was readmitted to Temple University Health Sciences Center on July 3 for repair of the atrial septal defect. The electrocardiogram was unchanged from that seen on the previous admission. A Sndergaard procedure was performed on July 5 to repair the atrial septal defect. A tracing taken that day (Fig. 8B) and again on July 6 (Fig. 9A) suggested a nodal or junctional rhythm. On July 8 a “rhythm strip” (Fig: 9B) with the use of lead II revealed an inverted P wave with a P-R interval of 0.08 sec. Unfortunately no other leads were obtained at that time. A 12 lead electrocardiogram was obtained on July 13 (Fig. 10) with a Schwarzer multichannel apparatus. THE

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Left Atria1 Rhythm The

P wave was found to be negative in leads II, III, In lead I the P wave was aVF and Vi through Ve. isoelectric. The P-R interval was 0.10 sec. and the QRS complexes were unchanged. A vectorcardiogram was performed on the same date (Fig. 11).

CASE 4. A 70 year old woman was admitted to Temple University Health Sciences Center on September 25, 1967, because of increasing ascites, hepatosplenomegaly, congestive heart failure, petechial hemorrhages and increasing fatigue. Physical examination revealed a well developed woBlood pressure man chronically ill in appearance. was 120/70 mm. Hg. There were petechiae and The neck veins were flat at ecchymoses on both legs. The heart was not en30’ and the lungs were clear. larged to palpatisan or percussion. There was no The second sound to the right thrill, rub nor heave. of the sternum was louder than the second sound to the left of the sternum. Distinct atrial and ventricular There was a grade gallops were heard at the apex. 2/6 ejection systc’lic murmur along the left sternal border. The rhythm was regular. There was obvious ascites, hepatosplenomegaly and peripheral edema. The initial electrocardiogram (Fig. 12A) taken on September 26 revealed a normal sinus rhythm, with left axis deviation and ischemic ST-T wave changes in the anteroseptal and lateral leads. After development of fever, chest pain and cough the next day, a repeat e1ectrocardiogra.m was taken (Fig. 12B) and revealed an increase in the ischemic The ST-T wave changes and a new pacemaker site. P wave was seen t,o be inverted in leads II, III and aVF, The P wave was flat with a P-R interval of 0.11 sec. and slightly positive in lead I. There was a flattened “dome and dart” P wave in lead Vi, a flat notched P wave in Vz and Vs and an inverted, low voltage P wave in V.I to Vti.

5B Figure

5. Case 1.

normal :rinus rhythm: VOLUME 22, NOVEMBER 1968

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SAGITTAL 4D

4E

4c

4F

4G

Figure 4. Case 1. Vectorcardiogram. Orthogonal electrocardiogram, and frontal, left sagittal and horizontal loop displays during “left atrial” rhythm.

A vectorcardiogram (Fig. tember 27.

13) was performed

Frontal,

on Sep-

RESULTS

Case I: The i&a-atria! electrocardiogram (Fig. 3A) indicated a PR complex high in the right

5E

5D Vectorcardiogram:

FR&TAL 48

right sagittal

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loop displays during

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aVR

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Figure 6. Case 2. A, Initial electrocardiogram showing normal sinus rhythm; B, electrocardiogram a week later shows rhythm arising “left atrial” during normal sinus rhythm.

atrium with two distinct components, a PnR’. As the catheter was advanced to the mid-atrium a Paa complex was seen, with the voltage decreasing as the catheter was advanced, and finally a Pas was inscribed in the low atrium. This sequence of configurations is directly opposite to that seen with sinus rhythm. As the catheter was withdrawn to a higher position, a Pa wave was finally found at the end of the tracing. Leads Vz to Ve continued to show left atria1 (or nodal) rhythm without changes in the P contour, thereby indicating that the observed changes were not due to a wandering pacemaker. In Figure 3B a sinus rhythm is indicated in the precordial leads. With the catheter in an upper atria1 position a Peg wave was seen, as expected with a sinus rhythm. The pacemaker then wandered toward the left atrium (or A-V junction), producing intermediate complexes, and finally a Pna was seen when an obvious inverted P wave appeared in the precordial leads. At times, despite identical P wave contours in the precordial leads, the intra-atria1 P waves varied, although the catheter was not advanced. This could have been caused by motion of the catheter. Figure 3C shows the transition

aVR

aVL

‘A

‘5

aVF

LONG

LEAD

II

from a sinus rhythm to a left atria1 (or nodal rhythm) in the space of 1 beat. The orthogonal electrocardiogram (Fig. 4) revealed the P wave directed entirely to the right in VX and entirely superiorly (and composed of two distinct components) in VY. In VZ the P wave was flat and essentially isoelectric. There was a tiny initial deflection anteriorly, a second tiny deflection posteriorly and a terminal anterior deflection. The frontal loop display (Fig. 4, B and C) revealed a completely superior orientation of the P loop to 270’. There was an extemely narrow loop, oriented superiorly with a clockwise rotation, initially slightly to the right and then minimally to the left. The left sagittal display (Fig. 4, D and E) again revealed the striking superior orientation with minimal posterior position of the P loop. It is difficult to be certain that the rotation is clockwise or counterclockwise because of the narrowness of the loop. In the horizontal display (Fig. 4, F and G) the P loop is so small in area that it is difficult to interpret other than to indicate a generally posterior and rightward orientation of the loop. With a return of sinus rhythm the shift in the P loop is evident (Fig. 5). In the frontal disTHE

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HORIZONTAL 7G Figure 7. Case 2. ittal and horizontal rhythm.

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7H Vecectorcardiogram.Frontal, left sagloop displays during “left atrial”

play the P loop was narrow, oriented inferiorly and slightly to the left with a clockwise rotation In the right sagittal display (Fig. 5, A and B). the loop was oriented directly inferiorly with a figure-of-eight configuration but neither an anterior nor posterior orientation (Fig. 5, C to In the horizontal display, the P loop was E). again small in area, and it was difficult to be certain of the d.irection of rotation, although the entire loop appeared to be oriented minimally anteriorly and to the left (Fig. 5, F and G). Vecforcardiograms were obtained, Case 2: but unfortunately not an orthogonal electrocardiogram. The frontal display (Fig. 7, A to C) revealed a directly superior orientation of the narrow P iloop, with no right or left direction to the loop and only one component. There was counterclockwise rotation of the loop. The left sagittal display was difficult to 1968 VOLUME22, N0VED~BF.R

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interpret. It appeared to show a bidirectional P loop with directly superior orientation to one segment and an inferior posterior orientation to the other. Its rotation was impossible to ascertain (Fig. 7, D to F). The horizontal display revealed an anterior and to the left direction (Fig. 7, G and H) of one component and a posterior and to the left direction of the other component of the P loop. Case 3: The orthogonal electrocardiogram (Fig. 11A) revealed a P wave of extremely low voltage directed slightly to the left in VX, entirely superiorly in VY, and isoelectric in VZ. The frontal display revealed a narrow loop directed almost directly superiorly, just to the left of 270”, in a clockwise rotation (Fig. 11, B and C). In the left sagittal display, the P loop was directed superiorly and slightly posteriorly in a narrow counterclockwise direction (Fig. 11, D to F). The P loop in the horizontal display, as with all these recordings, was difficult to interpret. The loop was small and its rotation equivocal. The loop appeared to be directed posteriorly and very slightly to the left (Fig. 11, G to I). Case 4: The orthogonal electrocardiogram (Fig. 13A) revealed a low voltage, notched P wave directed to the left in VX. In VY, the P wave was directed entirely superiorly. In VZ it was of very low voltage and directed minimally anteriorly. In the frontal loop display (Fig. 13, B and C) the P loop was seen to be directed to the left and superiorly, with a counterclockwise rotation. In the left sagittal loop display (Fig. 13D), the P loop was directed superiorly initially and then directed anteriorly in a counterclockwise direction. In the horizontal loop display (Fig. 13, E to G), the loop had a very small area and was directed anteriorly and to the left. The direction of rotation was difficult to ascertain. The jindings in the vectorcardiograms are summarized in Table I with the use of the Helms vectorcardiographic notation.14 DISCUSSION Mirowski’s conclusions concerning left atria1 rhythm were derived from vectorial analysis of the standard 12 lead scalar electrocardioSuch an analysis has the limitations gram.2-8 inherent in a noncorrected lead system in which alterations in position of the heart in the thorax and orientation of the chambers of the heart The Frank lead system may not be detectable. possesses the advantage of orthogonality, which

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P

FRONTAL

FRONTAL

(x2.5)

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Figure 10. Case atrial” rhythm.

3.

Electrocardiogram

TABLE

during “left

I

HORlZiNTAL

LWPS)

11G Vectorcardiogram. Figure 11. Case 3. Orthogonal electrocardiogram and frontal, left sagittal and horizontal

case NO.

Frontal

Left Sagittal

L

I

Vectorcardiographic Findings (P

R

Horizontal

loop displays during “left atrial” rhythm. 1

2

+2700 (Diirectly superior)

i-275” (Superior & slightly posterior)

+225O (Rightward posterior)

+2700 (Directly superior)

+270° (Directly superior component) -klO5” (Inferior & posterior component)

+3450 (Posterior & to the left component) +60° & to the left component)

&

(Ltcrior

3

+272O (Superior & slightly l&ward)

+275’ (Superior & slightly posterior)

+275O (Posterior & slightly to the left)

4

+2850 (Superior & leftward)

+2700 (Initially SUperiDr, then anterior)

+450 (Anterior & to the left)

provides spatial information unobtainable by conventional electrocardiographic methods. Likewise, the intra-atria1 electrocardiogram and the surface electrocardiogram do not correlate directly, although they approximate each other. VOLUME

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The former is able to detect changes in electrical activity closer to the source, unaffected by surface variables. The intra-atria1 electrocardiogram appears to be incapable of distinguishing left atria1 from nodal (A-V junctional) rhythm. The depolarization wave moves superiorly into the right atrium. As the catheter is advanced down through the atrium, a pattern directly opposite to that found in sinus rhythm is revealed. This information tells us that the pacemaker is originating inferiorly rather than superiorly. The pacemaker could be in the junctional tissue in the anterior and inferior aspect of the right atrium, or in pacemaker tissue at the base of the left atrium. One aspect of the last possibility that is troubling in light of our findings is the rapid wandering of the pacemaker from a sinus to an ectopic site, in 1 instance (Fig. 3C) in the space of one beat. It is

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aV1

aVI

aVR

V6 Figure 12. Case 4. Yift atrial” rhythm.

and

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A, initial electrocardiogram showing normal sinus rhythm;

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B, electrocardiogram next day showing

.

conceivable that wandering could occur from right atrium to left atrium as Mirowski et a1.2 have attempted to illustrate in several of their tracings. However, it seems more likely, in light of the conventional concepts of wandering pacemaker, that the pacemaker has wandered from the sinus node into nodal (or junctional) tissue. In analyzing the vectorcardiographic displays, we found that the P loop was directed superiorly, rightward and posteriorly in Case 1, in which the subject had an electrocardiogram This is most characteristic of left atria1 rhythm. somewhat contrary to the direction that one expects from the electrocardiogram by the analysis of Mirowski et al., namely, superiorly, rightward and anteriorly. This finding could be explained if the pacemaker originated from an A-V junctional site or from an anterior and inferior site in the left atrium.

In Case 3, the P loop was directed superiorly, posteriorly and slightly leftward. In this patient what appeared to be a nodal (or A-V junctional) rhythm developed after repair of an atria1 septal defect. The P wave was initially invisible (Fig. 8B), then appeared just before the QRS (Fig. 9A) and finally was found to precede the QRS by 0.10 sec. (Fig. lo), with inverted P waves in leads II, III, aVF and V1 through Vs. The last electrocardiogram thus fulfilled the criteria of a left atria1 rhythm, but the P loop was found to be spatially oriented in a direction suggestive of a nodal (or A-V junctional) rhythm. This discrepancy could be explained alternatively by postulating a site for pacemaker tissue located inferiorly and anteriorly, at the base of the interatrial septum in the left In any event, analysis of the electroatrium. cardiogram by the method of Mirowski et al. erroneously suggests a P vector directed superiorTHE

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13A FRON:&

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1x5)

P

R

(x2.5)

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L HORIZONTAL

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Figure 13. Case 4. Vectorcardiogram. Orthogonal electrocardiogram, and frontal, left sagittal and horizontal loop displays during “left atrial” rhythm.

Zy, to the right and posteriorly because of negative P waves in all precordial leads. Analysis of the tracings in Case 2 indicates the difficulties in vectorial loop analysis. There is a P loop with two components in the sagittal and horizontal planes with one component directed inferiorly, posteriorly and to the left, and another directed superiorly, posteriorly and to the left. The explanation may be a nodal (A-V junctional) site for the pacemaker or a site in the left atrium, anteriorly and along the interatrial septum, but not at its most inferior position. The clinical findings, suggesting digitalis intoxication, would be more consistent with an A-V junctional rhythm. Analysis of the electrocardiogram here suggests erroneously a rightward direction for the P vector because of inverted P waves in leads V1 through Vg. Analysis of the tracings in Case 4 revealed a P VOLUME

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loop directed superiorly, leftward and anteriorly. This direction is best explained by a pacemaker located in the A-V junctional area, although one would expect the loop to be directed posteriorly rather than anteriorly. It is difficult to postulate a left atria1 site initiating an impulse so obviously directed in a leftward direction. Whatever the site, an analysis of the electrocardiogram utilizing the method of Mirowski et al. suggests erroneously a mean P vector directed superiorly, anteriorly and rightward because of negativity of the P wave in leads V4 through V,. Several conclusions are warranted from these data: 1. If left atria1 rhythm is accepted as an entity, we have demonstrated a case which shows all of the electrocardiographic criteria in a patient without any demonstrable heart disease (Case 1). 2. We have performed intra-atria1 electrocardiograms and vectorcardiograms, for the first time to our knowledge, in cases which appeared to have the characteristics of a spontaneous left atria1 rhythm. By utilizing these methods we have found spatial orientation for atria1 depolarization which, although not negating a left atria1 site for pacemaker activity, suggests a more likely site in the nodal or A-V junctional area. In every instance the direction of the P loop differed from that suggested by analysis of the scalar electrocardiogram. 3. We strongly suspect, therefore, that the diagnosis of left atria1 rhythm by the electrocardiogram is still difficult and deserves further investigation utilizing the intra-atria1 electrocardiogram and the vectorcardiogram. After this work was completed, but before the data were sent for publication, two studies appeared in the literature to lend weight to our conclusion that the diagnosis of left atria1 rhythm based upon the criteria of Mirowski et al. is still questionable. Mirowski15 reported left atria1 rhythm in which P waves were upright in leads II,IIIand aVF and inverted in all the precordial leads, with a mean P vector directed inferiorly, to the right and posteriorly, thus suggesting a pacemaker located superoanteriorly in the left atrium. He failed to explain why the pacemaker might not be originating from the right atrium in these cases. He also described left atria1 rhythm in which P waves were inverted in leads II,III,aVF and in leads V1 through Vs, with a mean P vector directed superiorly, to the right and posteriorly, with a pacemaker located inferoanteriorly in the left atrium. However,

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in our Case 1 the electrocardiogram showed a “dome and dart” P wave in lead VI and an isoelectric P in lead VZ with a mean P vector directed to the right, superiorly and posteriorly. We postulated an A-V junctional or a left atria1 inferoanterior site for impulse formation. In our Case 3 the P vector was directed sufieriorly, posteriorly and slightly leftward, and we postulated either an A-V junctional site or a left atria1 inferoanterior location for impulse formation. Yet this patient’s electrocardiogram revealed inverted P waves in leads II, III and aVF and V1 through V6! It would seem that accurate analysis of direction for atria1 depolarization from the electrocardiogram is unreliable. In another recent studyi left atria1 stimulation produced P waves which did not conform to the left to right direction of depolarization as postulated by Mirowski. Marked variation in P waves in the surface electrocardiogram was Alobserved on stimulation in the same area. though the production of left atria1 rhythm by artificial means differs from the spontaneous variety seen in our cases and Mirowski’s, it nevertheless sheds considerable doubt concerning the validity of vectorial P wave analysis by the surface electrocardiogram. SUMMARY

An analysis of the intra-atria1 electrocardiogram and the vectorcardiogram was undertaken in 4 patients whose 12 lead scalar electrocardiograms suggested a so-called left atria1 rhythm. In all cases the direction of the P loop by vectorcardiographic analysis differed from the postulated direction obtained by analysis of In all cases a the scalar electrocardiogram. nodal (A-V junctional) site for pacemaker activity appeared more likely than a left atria1 site. The intra-atria1 electrocardiogram did not appear to be helpful in differentiating a nodal (A-V junctional) rhythm from a left atria1 rhythm.

We strongly suspect, therefore, that the diagnosis of left atria1 rhythm by the electrocardiogram is still a troublesome one, and deserves further confirmation utilizing the intra-atria1 electrocardiogram and the vectorcardiogram. REFERENCES 1. SOMLYO, A. P. and GRAYZEL, J. Left atria1 arrhythmias. Am. Heart J., 65: 68, 1963. 2. MIROWSKI, M., NEILL, C. A. and TAUSSIG, H. B. Left atria1 ectopic rhythm in mirror-image dextrccardia and in normally placed malformed hearts. Report of twelve. cases with “dome and dart” P waves. Circulation. 28 : 864. 1963. 3. MIROWSKI, M. Left atria1 ectdpic rhythm in a patient with rheumatic mitral insufficiency. Proc. Tel-Hashomer Hosp., 3: 119, 1964. Identification of the site of origin 4. MIROWSKI, M. of impulses in the atria by vectorial analysis of P waves. Isarel J. M. SC., 1: 456, 1965. Commentary on letter by E. 5. MIROWSKI, M. Kaplinsky. Zsarel J. M. SC., 1: 1048, 1965. 6. MIROWSKI, M. Left atria1 rhythm. Diagnostic criteria and differentiation from nodal arrhythmias. Am. J. Cardiol., 17: 203, 1966. 7. MIROWSKI, M. Rapid left atria1 rhythms. A report of two cases with “dome and dart” P waves. Israel J. M. SC., 2: 55, 1966. 8. ROGEL, S. and MIROWSKI, M. Experimental left atria1 rhythm. Israel J. M. SC., 2: 352, 1966. 9. ROTHBERGER,C. J. and SACHS, A. Rhythmicity and automatism in the mammalian left auricle. Quart. J. Exper. Physiol., 26: 69, 1935. 10. ABILDSKOV,J. A., BARNES, T. G., and HISEY, B. L. Studies of normal and ectopic atria1 excitation. Am. Heart J., 52: 496, 1956. 11. HOFFMAN, B. F. and CRANEFIELD, P. F. The physiological basis of cardiac arrhythmias. Am J. Med., 37: 670, 1964. 12. RUSKIN, A. and DECHERD, G. Momentary atria1 Am. electrical axes. III. A-V nodal rhythm. Heart J., 29: 633, 1945. 13. HECHT, H. Potential variations of the right auricular and ventricular cavities inman. Am. Heart J., 32: 39, 1946. 14. HELM, R. A. Vectorcardiographic notation. Circulation, 13: 581, 1956. Ectopic rhythm originating anter15. MIROWSKI, M. iorly in the left atrium. Analysis of twelve cases with P wave inversion in all precordial leads. Am. Heart J., 74: 299, 1967. 16. MASSUMI,R., and TAWAKKOL, A. A. Direct study of left atria1 P waves. Am. J. Cardiol., 20: 331, 1967.

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