Hypertrophic Cardiomyopathy

David Didlake

Firefighter / Paramedic

Acute Care Nurse Practitioner

@DidlakeDW

Peer review and commentary by Dr. Steve Smith

http://hqmeded-ecg.blogspot.com/

@SmithECGblog

It is early-summer, approximately 1330 hours, no cloud cover overhead, and 86 degrees with high humidity.

A 59 y/o Female calls 911 for crushing chest discomfort and difficulty breathing. Fire/EMS personnel find her laying supine on the kitchen floor, awake and verbal, although acutely ill. She reports having just finished a 10k run through the neighborhood. Her athletic apparel is drenched in sweat, however she is dry to the touch.

She reports a known history of Hypertrophic Cardiomyopathy (HCM) with left ventricular outflow tract obstruction and is on daily beta blocker therapy. During her jog she felt episodic palpitations and decided to take an additional beta blocker regimen upon returning home. Furthermore, she denies any hydration since conclusion of exercise.

As a brief review, HCM is a genetically inherited disorder that produces structural disarray in the myocardial cells. There is ventricular hypertrophy in the absence of abnormal loading conditions, such as aortic stenosis, or hypertension, for example – of which the most common variant is Asymmetric Septal Hypertrophy. Additional architectural changes include systolic anterior motion of the mitral valve, endothelial dysfunction at the level of the coronary arterial bed, and ventricular diastolic dysfunction. This last component is of particular interest since coronary perfusion occurs during the diastolic phase, and furthermore that these patients require adequate hydration to ensure optimal filling pressures to overcome the diffuse stiffness inherent to the ventricular walls.

The NIBP resulted 74/52 with a room air oxygen saturation of 90%. This is the initial ECG:

The QRS is widened with a regular cadence, and there are no discernable P waves. The rhythm appears Junctional – most likely the result of excessive beta blockade – with bizarre voltage disparities consistent with LVH. There is broad subendocardial ischemia as demonstrated by STE aVR with concomitant STD that almost appears appropriately maximal in Leads II and V5.

There is another concerning feature: the STE is not simply limited to the territories of aVR and V1. It is spread to V2 and V3. Lead aVL is spared of this STE, which is somewhat reassuring, but the fact that V2 and V3 perpetuate the STE vector is alarming. Remember, HCM is notorious for begetting coronary dysfunction, so these changes could be that of primary ischemia, as opposed to secondary in the context of chronic LVH-induced repolarization abnormalities.

One additional feature of this ECG is the apparent QRS widening (to an even greater degree) towards the end of the strip. The blue arrows indicate a similar QRS duration. The first green arrow shows QRS widening that appears to continue for the rest of the ECG.

These changes are most appreciable in continuous telemetry. Below is a section of the precordium with special attention to Lead V3.

The blue brackets denote a basic RR cycle length of 1000 ms at 60 beats per minute. The black arrow then shows where this predictable repetition fails as the rate becomes more bradycardic. The green brackets denote a revised basic RR cycle length of 1160 ms at 50 beats per minute. Incidentally, it is at this time in which the QRS grossly widens and becomes demonstrably fragmented (orange arrows, collectively).

Does this suggest a change in location of escape mechanism, specifically from Junctional to Ventricular?

These bradycardic changes are consistent with Phase IV (or, deceleration-dependent) conduction block of the His-Purkinje (His-P) system. In general, the refractory period of the bundle branches is dependent on the preceding RR cycle length. Thus, proclivity for block (even in the healthy left bundle branch) is established at low rates with progressive increases in cycle length. Moreover, diseased His-P cells have a less negative resting membrane potential during Phase IV of the conduction cycle, which inactivates sodium channels and renders them refractory to subsequent impulses with failure to fully depolarize.

An ECG was captured during this prolonged phase of widened, and equally fragmented, QRS.

There is LBBB-like morphology with persistent patterns of subendocardial ischemia. The V1-V4 discordant STE is not particularly excessive (as determined by m-Sgarbossa criteria), however there is appreciable concordant STD in Leads II and aVF. This worried the crew of potential acute coronary syndrome and STEMI was activated pre-hospital.

Smith comment: V5 and V6 are excessively discordant!!!! We found in both the derivation and validation of modified Sgarbossa criteria that an excessively discordant ST depression, as defined by 30%, was nearly 100% specific for “occlusion.” In any other patient, this would be diagnostic of occlusion. But I suspect that one could see a false positive in cases of HOCM, as we did not have any HOCM in our studies. So it is possible that this does not represent occlusion even though our studies would say it does.

She received a 1000mL NS fluid bolus, in addition to ASA administration, during transport. The hemodynamics modestly improved to a trending systolic NIBP of 100 mmHg with equally improved SpO2 values. Upon arrival at the receiving facility she verbalized some improvement, however advised lingering chest discomfort. Below is the initial ED ECG.

There is Sinus Brady with improved conduction as noted by the tighter QRS duration. The S-wave voltage in Leads V3 (19mm) and V4 (15mm) equals 34mm, and thus fulfills Peguero criteria for LVH in the adult female patient.

It is not unexpected to encounter secondary repolarization abnormalities in the setting of LVH, however the overall pattern of subendocardial ischemia lingers with persistent chest discomfort. Furthermore, given the primary negative QRS deflection in V4, I would expect at least some amount of discordant STE here, but the J-point actually drops below the isoelectric line in a concordant manner. A similar pattern is appreciable in Leads II, III, and aVF. Are these findings consistent with a particular coronary distribution? Even if one can argue that no such distribution match exists, they are – at the very least – grossly abnormal.

How can we reliably identify OMI in the setting of LVH?

Hyperacute T waves (HATW)

The presence of true HATW, I think, is applicable to any preexisting pathology encountered. As has been elucidated in previous posts, HATW’s classify as Grade I in the Sclarovsky-Birnbaum ischemic triage for occlusive MI. This grading system is the time sensitive prelude to Q-wave (irreversible transmural scar) formation. When OMI is captured in this early phase, there exists the highest amount of salvageable myocardium and least likelihood of heart failure at hospital discharge.

Here are two examples of HATW’s in the setting of confirmed LVH.

100% RCA occlusion

V4-V6 are actually V4R, V8, and V9, respectively

95% RCA occlusion

Concordance and Discordance

Smith reported faults in the Armstrong report that an ST/S ratio of >25% was sufficient to diagnose STEMI in the presence of LVH by means of excessive discordance. As it currently stands, an ST/S ratio >15% should raise awareness for new anterior STEMI. Convex morphology, or STD V5-V6 with STE aVR, in isolation, is not particularly helpful as these findings commonly occur in uncomplicated LVH.

Concordance, however, is pretty striking – and has been equally helpful in some of my previously encountered situations. Below are two examples of this.

99% LAD occlusion

“Inappropriately baseline” ST in V2

Concordant STD V3-V4

Leads I, V5, and V6, are excessively discordant to the naked eye

Lead III manifests an Aslanger-type STE

95% LAD occlusion

Concordant STD V3 and V4

Back to the case

The patient did not respond to medical therapy. Cardiology felt her chest pain to be, most likely, the result of coronary supply-demand mismatch in the context of HCM endothelial remodeling (i.e. Type II MI), however decided to pursue coronary angiogram out of an abundance of caution. A mid-LAD culprit lesion was identified and stented. Unfortunately, I don’t have specifics on pre- and post-procedural TIMI flow, but the Troponin I peaked at 6.140 ng/mL.

Smith comment: It is highly likely that it was open with flow at the time of the angiogram, given how much she was improved by the end of her ED stay.

This case provides a constellation view of the many sequelae associated with HCM – preexisting disparities of coronary perfusion due to endothelial remodeling, exacerbated diastolic dysfunction when volume depleted, conduction disorders in the diseased His-P system, and thrombosis from microvascular coronary disease.

References

Naidu, S. (2015). Diagnosis and management of hypertrophic cardiomyopathy: Expert analysis. American College of Cardiology.

Tower-Rader, A. & Desai, M. (2019). Manual of Cardiovascular Medicine (5th ed.). Chapter 10: Hypertrophic Cardiomyopathy (pg. 130-141). Wolters-Kluwer: Philadelphia, PA.

Josephson, M. E., et al. (2017). Paroxysmal atrioventricular block: Eletrophysiological mechanism of phase 4 conduction block in the His-Purkinje system: A comparison with phase 3 block. Pacing Clin Electrophysiol. 40; 1234-1241.

Smith, S. W., et al. (2018). New insights into the use of the 12-lead electrocardiogram for diagnosing acute myocardial infarction in the emergency department. Canadian Journal of Cardiology, 34; 132-145.