Normal PR Interval Research Articles

First heart sound: A phono‐echocardiographic correlation with mitral, tricuspid, and aortic valvular events

We evaluated the relationship of S1 recorded by phonocardiography at the mitral area with motion of the mitral, tricuspid, and aortic valves, recorded by simultaneous echocardiography in 20 cardiac patients with a normal PR interval. The first major component of S1 coincided with mitral valve closure in 20 of 20 patients (100%) and also with tricuspid valve closure in 14 of 20 patients (70%). The second major component of S1 coincided with aortic valve opening in 20 of 20 patients and also with tricuspid valve closure in six of 20 patients (30%). We conclude that the first major component of S1 coincides with mitral valve closure in all patients but may also coincide with tricuspid valve closure in many patients, and the second major component of S1 coincides with aortic valve opening in all patients but may also coincide with tricuspid valve closure in some patients.

Recurrent tachycardias due to an accessory pathway

A 48 year old female presented with a long history of palpitations and syncopal episodes. His bundle electrogram studies were performed in order to evaluate the conduction system. The electrocardiogram (ECG) revealed normal PR and QRS intervals, while the unpaced His electrogram was normal. With atrial pacing rates of 110 to 180 beats/min, the AH and HV intervals remained essentially unchanged. This signifies that there was an accessory conduction pathway which bypassed the AV node. Thus, pre-excitation can not be eliminated as a diagnostic possibility even if the ECG is normal.

Reciprocal rhythm in patients with normal electrocardiogram: Evidence for dual conduction pathways

The present study refers to six patients in whom an A-V reciprocal rhythm could be documented; in four cases it took the form of sustained tachycardia. None of the patients showed any ECG feature of ventricular pre-excitation (PR interval of more than 0.12 sec. and normal QRS configuration). The extrastimulus method showed, at first, that the A-V conduction time of the premature beat varied only slightly with the decrease of the coupling interval. From a critical A1A2 interval there was a sudden lengthening of A2H2 preceding the occurrence of re-entrant beats. The curve of H1H2 responses reflected these changes, showing two distinct parts. The second part following the slowing of the impulse included the initiation zone of atrial echoes and of reciprocating tachycardia. These results suggest the existence of two A-V pathways, one fast and the other slow. The point at which the break between the two parts of the curve occurred might be related to the effective refractory period of the fast pathway. In the same way, when atrial pacing reached a critical rate, it induced an abrupt increase of AH in five cases. In the sixth patient, A-V conduction time remained unchanged up to 170 per minute. Ventriculoatrial conduction was always observed, the delay of which did not lengthen with the rate. In one case tachycardia could be induced by a premature ventricular beat without lengthening of the V-A time. It is concluded that in spite of a normal PR interval, the presence of dual A-V pathways may be implied in the genesis of reciprocal rhythm.

Atrio-His bundle tracts.

The atrio-His bundle tracts are very rare; only two have been found in 687 hearts studied histologically. These tracts have a similar appearance to those of the atrioventricular bundle and form a complete bypass of the atrioventricular node. In their presence the electrocardiogram may show a short or normal PR interval. They may be responsible for some cases of very rapid ventricular response to supraventricular arrhythmias.

His bundle electrogram in patients with acute myocardial infarction complicated by atrioventricular or intraventricular conduction disturbances.

Seventy-two patients with acute myocardial infarction complicated by atrioventricular or bundle-branch block or a combination of both had His bundle electrogram studies performed during their stay in the coronary care unit. In 19 of the 72 patients a repeat His bundle electrogram was performed before discharge from hospital. These studies demonstrated that 30 of the 32 patients with atrioventricular block and narrow QRS complexes had a block above the origin othe His spike (proximal block). Eleven patients in this group had repeat His bundle electrograms performed before discharge and in 3 patients there was evidence of residual atrioventricular nodal dysfunction. Both the hospital and follow-up mortality in this group was low and there was no evidence to suggest that permanent pacing would benefit these patients. Of the 18 patients with bundle-branch block and a normal PR interval, 9 had prolongation of the HV interval, but there was no difference in mortality in patients with normal or prolonged HV intervals. Twenty-two patients with bundle-branch block also developed atrioventricular block. In 5 of these patients the site of the AV block was proximal and in 14 it was distal, while 3 patients had both proximal and distal block. The hospital mortality in those patients who progressed to second- or third-degree atrioventricular block was considerably higher than in those patients who remained in first-degree atrioventricular block.

Multiform Wolff-Parkinson-White syndrome

Summary A case of Wolff-Parkinson-White syndrome is described. The patient exhibited atrial fibrillation (AF), sinus rhythm (SR) and attacks of supraventricular tachycardia (AT). Five types of QRS appeared. Type R1 was observed during AF, SR, and AT. It was normal in configuration and, during SR, was preceded by a normal PR interval. Type R2 had some features of the WPW syndrome and appeared only during AF. Types R3 and R5 had all typical features of WPW syndrome and occurred during SR. Type R4 appeared very occasionally in SR and was probably a transitional form. The distribution curve of R-R1 and of R-R2 intervals during AF showed peaks bearing a simple arithmetic ratio to each other. A change in heart rate during SR was associated with a change in QRS pattern. The slowest heart rate was associated with R3, the fastest with R5 and the intermediate with R1 QRS type. A lidocaine drip had the following effects: increased the relative height of the slower over the faster peaks in the distribution curve of AF without changing the value of the peaks; reduced the proportion of R2 over R1 during AF; stopped AF; reduced the proportion of R3 and R5 over R1 during SR; and reduced the occurrence of AT. The mechanism of these phenomena is discussed and the analogy to coupled oscillatory systems is stressed.

Pre-excitation with Normal PR Intervals: A Case Secondary to Slow Kent Bundle Conduction

His bundle electrograms were recorded in a patient with pre-excitation and normal PR intervals to determine whether conduction was via anomalous A-V connection (Kent bundle) or infranodal bypass (Mahaim tract). During sinus rhythm (62/min) both P-delta and P-H measured 155 msec. With atrial pacing at 70 and 75/min, P-H prolonged while P-delta remained constant. At 80/min, the anomalous pathway failed and the QRS normalized. The effective refractory period (ERP) of the anomalous pathway was 700 msec. In summary, the normal PR interval represented slow Kent bundle conduction. Additional findings of depressed Kent bundle conduction included a prolonged ERP and block at a slow paced rate, implying that tachycardia would be unlikely. In WPW, the functional properties of both normal and anomalous pathways can be determined by His bundle recording and atrial pacing.

Atrioventricular conduction defects in patients presenting with syncope and normal PR interval.

Atrioventricular conduction defects in patients presenting with syncope and normal PR interval.

Retrograde Ventriculoatrial Conduction in Patients with Acute Myocardial Infarction

Temporary transvenous pacemakers were inserted in ten patients with acute myocardial infarction complicated by atrioventricular (A-V) block. With return of sinus rhythm, the ventricular rate was intentionally increased above sinus rate by graded increases of the pacemaker rate and stimulus amplitude to a maximum of 120 beats/minute and to 12 milliamperes for each paced rate. Four patients had ventriculoatrial (V-A) conduction at paced rates greater than the sinus rate. Two of four had V-A conduction at slower rates (80–100 beats/minute), but A-V dissociation developed with more rapid rates (100–140). Three of six patients who had sinus rhythm with normal PR interval demonstrated V-A conduction while only one of four with first degree block showed retroconduction. The pattern of conduction was independent of stimulus amplitude. Retrograde V-A conduction occurs commonly in patients with acute myocardial infarction with slow ventricular rates (80–100 beats/minute) and less commonly with rapid rates. Temporary transvenous pacemakers were inserted in ten patients with acute myocardial infarction complicated by atrioventricular (A-V) block. With return of sinus rhythm, the ventricular rate was intentionally increased above sinus rate by graded increases of the pacemaker rate and stimulus amplitude to a maximum of 120 beats/minute and to 12 milliamperes for each paced rate. Four patients had ventriculoatrial (V-A) conduction at paced rates greater than the sinus rate. Two of four had V-A conduction at slower rates (80–100 beats/minute), but A-V dissociation developed with more rapid rates (100–140). Three of six patients who had sinus rhythm with normal PR interval demonstrated V-A conduction while only one of four with first degree block showed retroconduction. The pattern of conduction was independent of stimulus amplitude. Retrograde V-A conduction occurs commonly in patients with acute myocardial infarction with slow ventricular rates (80–100 beats/minute) and less commonly with rapid rates.

Therapy of Atrioventricular Block

First-Degree Block PROLONGATION of the PR interval beyond 0.20 second may occur in many disorders including acute myocardial infarction, aortic stenosis, severe aortic insufficiency, adrenal insufficiency, rheumatic fever and a number of systemic infectious diseases. An occasional normal person will have first-degree heart block in the absence of any apparent disease. Although an optimal role for atrial contraction may be provided by a normal PR interval, the delayed onset of ventricular contraction in first-degree block rarely produces significant changes in heart function. A prolonged PR interval will usually return to normal with atropine or sympathomimetic agents, but treatment of this . . .